Home Forums Hunting & Shooting Long Range Hunting Bullet Shape Relative to G1 and G7 at Supersonic Velocity

My agreement has nothing to do with it. Facts don�t care who agrees with them. When an incorrect statement is attributed to somebody it�s always a good idea to go back to the original source and verify. It�s possible much was lost in the translation.

Your statement is true, but you want to limit �supersonic velocities� to mean something other than �supersonic velocities?� That would be a different statement.

OK, even staying well within your Mach 1.2 limit (since you have the luxury of not worrying about where it really gets hard) your own data still shows error of 5.1� with one method and zero with the other at only 1300 yds. How exactly does five inches of error become �just as good as� zero inches of error? What does �just as good� mean to you, exactly?

Tell that to the target you just missed. Have you ever actually tried to shoot something at 1500 yds and hit it with your first shot? If you ever do, you may realize that you need an additional six inches of error on top of all the other potential errors inherent in making such a shot like you need a hole in the head. Especially when simply using more accurate data to which you have access can eliminate it. 5.1� at 1300 may even be worse as a percentage of �how far you miss with the first shot.�

A given velocity is only a single point on a curve. It tells you nothing about how good a match the bullet is for the rest of the curve.

Wrong. It�s a value. Not a predictor of other values. A curve is many values of one variable plotted against another, a single value is only a single point on the curve. Even an average tells you nothing beyond the average value�a vertical line and a horizontal line can have the same average value.

Without even getting out of the 6mm�s, Bryan�s data shows the Nosler 95 Partition, which has an average G7 I of 1.303 is actually a better match to the G7 curve than the bullet you chose, having only � the variation in form factor over the measured velocity range. And the Sierra 107 Matchking has an average I7 of 0.993�should be a �perfect match,� eh? Wrong. It has over seven times the variation the Nosler has. It�s actually a much better fit to the G1 curve than it is the G7 curve (even though its G1 I of 0.508 is quite a ways off from the �perfect� 1.0).

Again, this relies upon your definition of �significant.� If the targets you shoot at 1300 yds are so large that 5� is not significant, you might learn more by shooting at smaller targets.

Well OK then. You have a couple responses to one thread on this board. Obviously a new law of exterior ballistics has been created!

While some bullets don�t do so well below that and keeping above it means you never have to worry about it, it�s far from some all encompassing limit which means a ballistics method that ignores everything beyond it should be adopted as the industry standard. Many of us go below that all the time. My 6.5 Grendel would be pretty much worthless beyond 700 or 800 yds with typical loads if that was the limit. I have way too many sub-MOA groups at 1000 and even 1100 yds to know the right bullets can be fairly accurate well below that velocity.

Wrong. With a 300 yd range you can measure the drag of the bullet at different velocities by launching it at different velocities. With multiple data points, you can draw a curve. While far from ideal, you can get a boatload more information than a single TOF measurement from it.

Wow, I�ll bet nobody using that thing had ever thought of any of this before! I�ll bet they had no idea what a waste of money it was�. Seriously, I think you�re insulting the intelligence of the people.

The last time I checked, 2000 fps was supersonic. Another new rule?

Another 5� off is �better� than �right on� sort of way?

Again, the only data you have provided shows worse, not �better� results.

OK, let�s try to explain this again:


It�s really very simple. While Sierra doesn�t make as many VLD-shaped bullets as Berger, one I�ve used a lot is the 30 cal 210 SMK with listed G1 BC�s of: .645 @ 1800 fps and above, .630 between 1600 and 1800 fps, .600 between 1400 and 1600 fps, .530 @ 1400 fps and below.

In my above comparison, if you shoot this bullet from a big magnum at 3500 fps, for a large portion of the flight from muzzle to subsonic the bullet will have a G1 BC of .645+ (actually higher if you look at Bryan's data). This will increase its average G1 BC from the muzzle to subsonic.

If you shoot it from a smaller round with a MV of 2000 fps, it will spend very little time at .645 (actually it'll stay lower according to Bryan's data) and thus will have a much lower average G1 BC for the entire flight from muzzle to subsonic.

Two markedly different G1 BC values. Which would you print on the box? Which would you declare as "accurate?"

When you look into the numbers you�ll see this is exactly what is happening with the bullet you chose for the comparison (using Bryan�s G1/velocity data in place of Sierra�s). See below:


It suggests that to you because you don�t understand what is going on. There is no relationship from which you can form this conclusion.

Assigning a single G1 BC to a bullet which does not follow the G1 curve well is an inherently inaccurate exercise. Your discovery of this is no discovery at all and is not evidence of similar inaccuracies in the G7 values because the bullets follow the G7 curves much more closely, which makes that a fundamentally different problem.

A single G1 value for such a bullet will only be correct for a single set of conditions. If you change those conditions it�s likely the value will be wrong. Berger is damned if they do, damned if they don�t. It�s a lost cause�which is why they�ve switched to G7 for their bullets.

Case in point: You came up with a �more accurate� G1 value for that bullet�.under specific conditions you chose. Under different conditions, such as a lower muzzle velocity, the G1 value Berger advertises will be more accurate than the G1 number you came up with. Re-run and post the numbers you did in the very first post except change the muzzle velocity to 2500 fps. Which value is the �most accurate� now? As you can see, trying to put a single G1 BC on that bullet is inaccurate the way Berger does it, and the way you did it.

Hopefully that exercise will make you understand the folly of trying to use a single G1 value for a bullet that follows the G7 curve. When you look at the data, it�s obvious how that inherent inaccuracy of doing so in no way reflects upon the accuracy of using a single G7 value which will give accurate results for both velocities for a bullet which follows the G7 curve.

As you can see above, it may be annoying to study those numbers until you understand them, but after you do you will see no progress is made with your method at all. The real progress is made by using drag models which match the bullets� actual drag curves very closely. When that is done, a single BC can be pretty accurate for a bullet under any set of conditions. When the bullet�s actual drag curve is very different from a standard drag curve, any single BC of that drag curve will be a poor description of that bullet for all conditions no matter how you come up with it.

Naturally, there are some bullets that don't follow either curve very well. With multiple measurements such as are presented in Bryan's book, it is easy to identify such bullets so that you may come up with specific strategies to deal with them. With a single TOF measurement only, you'd never know.

Go look at Bryan's book and check his data points and you see that he only tests bullets from Mach 1.2 to about Mach 2.7. That's the same velocity range I'm using. Obviously, he understands how such bullets will be used. Are you willing to concede there's a practical velocity range or do you just what to argue for the sake of arguing?



The part you're missing is neither one can be exact because of random variations such as MV. Most rifles a person can carry on a hunt produce groups of at least 0.5 MOA which is 6.8 inches at 1300 yards. From an engineering standpoint any signal that's below the level of noise is insignificant as it can't be reliably measured. If you want to brag about how incredibly accurate your rig is and that you can reliable shoot less than 0.5 MOA groups at 1300 yards go ahead and make that claim. Most of us know better.



You need to brush up on your math. I gave you this equation yesterday. Form factor is the actual bullet's drag coefficient divided by the standard bullet's drag coefficient at a given velocity.

Now substitute the standard bullet's drag coefficient in the numerator for the actual bullet's drag coefficient. Now you have the drag of the standard bullet divided by the drag of the standard bullet and any number divided by itself is 1. Thus, all standard bullets have a form factor of 1.0 at all velocities. An actual bullet that perfectly matches a standard bullet also has a form factor of 1.0 at all velocities. An actual bullet that has an average form factor of 0.9972 is going to be a close match to the standard bullet over the velocity range the actual bullet was tested at. This is just the cold hard facts of math.



In general that's true, but we're talking about two specific curves here and perhaps I know something you don't. Below is a chart showing the G1 and G7 drag profiles where G1 has a BC of 1.000 and G7 has a BC of 0.500. In the center is a velocity zone between Mach 1.7 and 2.6 (1900 to 2900 fps) where the two drag functions coincide in a nearly exact relationship of 2 to 1 and then diverge above and below that velocity range.



What this means is no bullet of any shape or construction can exhibit a change in G1 BC within this velocity range without also changing by the same percentage relative to the G7 BC. In this important velocity range G1 BCs are as good a predictor as G7 BCs.

I don't expect you to take my word for it so you can test this for yourself on the JBM site by picking any G7 BC and doubling it to get an equivalent G1 BC for this velocity range. For example, using a G7 BC of 0.279 at 2900 fps MV the velocity at 650 yards is 1901.5 fps. For a G1 BC of 0.558 at 2900 fps MV the velocity at 650 yards is 1905.1 fps. Compare drop and you'll find that it remains within 2 inches out to 1100 yards even though the velocity has dropped to about Mach 1.2 at that range.

Looking at the chart you'll see that on the left in the low velocity zone the G1 line is below the G7 line, but on the right in the high velocity zone the G1 line is above the G7 line. This means we can extend the velocity range in which the G1 closely matches the G7. For example, on the JBM site I increased the MV to 3200 fps using the G1 and G7 BC values from before. At 800 yards the G1 BC has a velocity of 1929.6 fps and the G7 BC has a velocity of 1931.0 fps. Furthermore, drop remains within 2.2 inches out to 1400 yards.

In theory G7 BCs are a better predictor for VLD bullets in the transonic velocity zone, but that's only important for the long range shooters who believe they can maintain accuracy at such ranges. From the "Determining a Load�s Maximum Range" topic, that seems to be very few shooters. I say in theory because checking Bryan's book (1st edition) I don't see any data points below about Mach 1.2 and for most bullets, the lowest data points are around Mach 1.5, so he doesn't have any real data for VLD bullets going subsonic, at least not in the 1st edition. I don't consider that an oversight, only that being a long range shooter himself, Bryan realizes that long range shooters stay above about Mach 1.2.



If you take the G1 BC of 0.645 in the 1800 fps range and divide it by 2 for a G7 BC of 0.323 and plug them into JBM with a MV of 3500 f/s you'll find that the drop is within 2.7 inches out to 1000 yards even though the MV is outside the G1 � G7 drag convergence velocity zone. Bryan publishes a G7 BC of 0.316 for this bullet and plugging that number into JBM the drop is within 0.8 inches at 1000 yards and down to 0.3 inches at 1300 yards. If I reduce the MV to 3000 fps then the G7 BC of 0.323 is within 0.1 inches at 1000 yards and at 1.2 inches at 1300 yards.

A simple dividing of the G1 BC by 2 results in a G7 BC that gives trajectory predictions that are well within the normal group size of any hunting rifle out to 1300 yards for loads with muzzle velocities of from 3500 to 2800 fps using this bullet.

I expect Bryan's G7 number is more accurate outside the MV and range envelope I defined, but I didn't have to measure anything to get results that are practically the same for most long range shooting.

As for loading this SMK bullet to a MV of 2000 fps, its pure hypothetical. I don't know of any long range shooter in their right mind who would waste their time on such a load

The reason G1 has been so successful is not because it produces higher values, as some suggest, but because it's almost as accurate as G7 for VLD bullets in the velocity range where such bullets are used and it's more accurate than G7 for non-VLD bullets. G1 is the best all around standard and this allows shooters to compare bullet ballistics between all types of bullets from most manufactures.

The equal TOF technique I've been explaining takes advantage of G1's nearly exact 2 to 1 match with G7 over much of the usable small arms velocity range and its better match to non-VDL bullets.

Think about the chart I posted and what else it means. It has implications beyond what I've reveled so far, but at this point I don't think anyone but ballisticians care.

G1 and G7 refer to standard projectiles used in ballistics research. If you use any exterior ballistics calculator or program, the Ballistic Coefficient numbers you enter are assumed to be G1 unless labeled as something else. Berger bullets publishes both G1 and G7 BC numbers that you don't want to swap when working with an exterior ballistics calculator. The argument going on is about how best to measure BC values and which gives better results. In practice, it makes no difference to most people.

As I said, the source was cited. If you wanted to check you had all the information you needed to do so. You come across as one of those guys who wants links for the sake of links.



This is where you lost a lot of credibility, its 6th grade math that all standard bullets have a form factor of 1. A bullet that matches a standard bullet also has a form factor of 1. Your example Nosler bullets form factor values are further off 1.0 than 0.993. Don't tell me you think a form factor value over 1 means the bullet is a better match to the standard than something with a value of 1. That would be too funny.



Remember you're not the only one reading posts. Some of us want such detailed background info when a person then goes on to make a conclusion. It's what the better professors did in my college years. No one should take that as an insult let alone someone who forgot 6th grade math.

That's an eye opening graph you posted. I don't remember seeing anything like it before where the G1 and G7 are scaled. That explains lots including why the simple trick of just halving the G1 to come up with the G7 works so well.

I do agree with JonA in the sense of not wanting to abandon or down-play what Bryan is doing. He's done all shooters a great service in writing his book without which there would be little real data to compare and ponder. He also knows a lot about long range shooting few can match.

I'm not a ballistician, but I do want to learn more about the subject, so keep it coming.

I hope I�m not coming across as trying to down play what Bryan has done. If so, that's not my intent. Nonetheless, in order to discuss the merits of G7 there's no other source of widely available data to cite.

As it appears you�ve turned off all your �comprehension� and �learning� brain cells and poured caffeine on the �defense mechanism� ones, I�ll try and make this short and sweet so you can focus. I still think I can break through to you. Just concentrate on the facts presented.

How exactly do you believe he measures a bullets BC AT Mach 1.2? How would you measure the BC of a bullet AT Mach 1.2? Shoot it at that velocity over an �instant BC generator?� Or measure the velocity drop or TOF a ways above and below so you get an average at that velocity?

Your scientific method is flawed. That other variables may not remain constant does not excuse the inaccuracy of another. It�s not just a copout of your ballistics argument, it�s not a scientifically valid one. Have you heard of a thing called a �scatter plot?� Real Engineers use them all the time. So do shooters�they just call them �groups.�

Which part of �a� velocity do you not understand? You are talking about a CURVE in which the X-Axis is VELOCITY. To populate that curve you either need an equation that defines drag as a function of velocity�which you don�t have�or you need to measure the value (drag) at different velocities. Bryan did the later. You are doing neither. You are �assuming� data which does not exist to draw your curve. Your curve is an imaginary one.

Again, you are describing a curve for which you have no data. You are using imaginary data to populate the curve. Try using actual measured data for the 107 SMK as suggested. The numbers are right in front of you in black and white. Actual measurements. You can only burry your head in the sand so long.

First, note how widely divergent they are at the 3500 fps muzzle velocity you began the thread with (and remember what happens at the muzzle affects the entire rest of the flight).

Secondly, you need to acknowledge that real life bullets may not follow either curve, so that chart means nothing with respect to the above. In fact, virtually all bullets will diverge from one of the curves at least a little bit. It would be a rare bullet indeed that followed one of the curves exactly . This is why actual values must be measured. Bryan isn�t doing all those measurements just for his health.

I wish you would have spent that effort on the real comparison I suggested, or re-doing your �real, accurate� numbers from the beginning of the thread as I suggested. Let�s do one, it�ll be undeniable.

Wrong, as you would have seen had you done the example. But just to make you happy, we�ll do it staying above Mach 1.2 to eliminate that from your quiver of excuses.

Have you ever heard of the 6.5 Grendel? 6mmAR? BR? SPC? Etc? While not the first choice for hunting, where you actually need to kill something, a bullet doesn�t need to be going fast to punch a hole in a piece of paper. Dave T was using the 240 SMK out of a .308 for a while�.

What rounds to you believe people are using to shoot the 115 Berger at 3500 fps? I guarantee you it�s a pretty small percentage that get launched that fast.

But to eliminate that excuse from your quiver as well, we�ll do the below example at 2500 fps instead of 2000. I�m really stacking the deck in your favor here, if your conclusions were accurate.

So you fudged the numbers to reduce the error to �insignificant� levels by your standards�. You keep claiming something is �more accurate� but then keep defending its increased error as �insignificant.� If it was more accurate you wouldn�t have to keep doing that.

I don�t know if you were being lazy or if you somehow knew if you had run the numbers as suggested you would have been proved wrong so you avoided it. Either way, I�ll do it for you. Please, follow along.

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Let�s pretend that bullet follows the G7 curve exactly. It has an average form factor of 1.0000 so it must, right? It actually doesn�t but you may still be wrestling with that so let�s just pretend that it does.

At standard conditions, launched at 3500 fps its TOF is 2.205 s to 1600 yds (stays above Mach 1.2). This equates to an average G1 BC of .637. That is the exact measurement method you advocate in the beginning of the thread.

At standard conditions, launched at 2500 fps its TOF is 1.550 s to 950 yds (stays above Mach 1.2). This equates to an average G1 BC of .621.

So, which do you print on the box? According to your first post, you would print .637 and believe it is �more accurate� than the G7 BC Berger prints somehow and you believe that is what Berger should do. It would be pretty accurate for a 30-378 with a 30� barrel.

But some poor schmuck out there is going to load it in his .308 and use your .637 G1 BC value because that�s what is printed on the box. What happens? He misses, that�s what.

Your .637 �accurate� G1 BC value says he�ll have 338.5� of drop from a 100 yd zero when launched at 2500. If you had used the .621 value which will be much more accurate for a 2500 fps muzzle velocity, the predicted drop would have been 343.2�. That�s nearly 5� of error at only 950 yds. That�s using the exact method you outlined as being �more accurate� at two reasonable velocities for different rifles. That�s staying above Mach 1.2 where you say there will be no significant difference�go below that and it gets worse. Do the comparison at 2000 fps like I originally said and it�s worse.

Of course I shouldn�t have to remind you that for a bullet that follows the G7 curve, a single G7 BC printed on the box will give accurate results for both rifles, at both velocities.

Do the exact same comparison for the bullet you posted in the beginning of this thread and you�ll see the exact same thing. Don�t come back with some meaningless argument about how hunting rifles have such crappy accuracy we�ll never notice the difference, therefore your less accurate method is actually more accurate�.

Run the numbers! Tell us what your �more accurate� average G1 BC for the 115 Berger from a gun that shoots it at 2500 fps. Then try and explain why it�s something different than .559 but we should still agree .559 is the most accurate!

Since you can see the numbers plain as day, can you now give me one single reason why �the industry� should try and put a single G1 BC on bullets that more closely match the G7 curve?

You began this thread with the assumption that the difference in G1 BC�s was due to poor methodology by Berger/Bryan. By now, the lightbulb should be going on for you. You should realize the difference was cause by the inherent problem of describing a G7 Bullet with a G1 value�it will never be correct for all the rifles that will use it. And since the error clearly is not caused by methodology, your assertion that it brought the accuracy of their G7 published values into question was without cause.

Cited? Quoted? Mis-Quoted? Paraphrased? If somebody goes around saying 2+2=5 and lists me as the source, I would hope people would come to me and verify before making assumptions.

Maybe lost credibility with a 6th grader who doesn�t know what a coefficient is or what it is for. A coefficient simply scales a curve up or down. Hopefully my explanation above covered this for you. A FF of 1.0 at a certain velocity simply means the bullet�s actual curve crosses the theoretical G7 curve at that single point. It means nothing about how close the curves are over the rest of the graph. The rest of the curve could be wildly different.

The shape of the curve is what matters. This is what is programmed into your ballistics program. How far away from the X-Axis the curve is (a form factor of 1.0 vs. 1.3) has no influence on the accuracy of your results. This is why you input the ballistic coefficient into your program, so it can scale the curve up or down and give you the proper results. If the bullet�s actual curve is much different from the theoretical drag curve, you will get inaccurate results even if the bullet�s average form factor is 1.00000000.

That�s simplified, but hopefully it works for you.

You know; I have been told that Jeff and I can really get into nano-nit picking. I now know that impression is totally wrong. My good friend Jeff and I are pikers compared to you hosers. Talk about killing electrons for no good reason.

Says the guy who always gets spotter shots to discover both windage and elevation before he pulls the trigger for real. If the idea of a first round hit is lost on you, that's fine. I won't call you a hoser for it.

Hmmmmmm

Boy, was I wrong or what?

Go look at Bryan's drag coefficient charts where he calculates BC. They all show his data points. Please read the chapter where Bryan explains how to read his data.



Every shot is subject to random variations in MV and barrel movement and these variations produce "groups" as you acknowledged even when shooting indoors using a machine rest. When a manufacture brags about how accurate their rifles are they say they are Sub-MOA, meaning they produce "groups" of less than 1 MOA. Check out the Weatherby site if you don't believe me. You can argue that variations less than 0.5 moa are significant all day long, but most shooters and manufactures know better.



Anyone can take a single sentence out of contest and argue against it. I did say "at a given velocity" in that sentence and then went on to expand the definition for velocity ranges in the following sentences. How did you miss them?



I picked the 115 Berger because Bryan has 18 data points for it as compared to only 6 data points for the 107 SMK. The more data the more accurate the form factor and variation data is going to be. Had Bryan tripled his testing of the 107 SMK the results would likely have been different. Furthermore, Burge publishes the G7 BC for their bullets and Sierra doesn't. For a valid and fair comparison I wanted to use a manufacture's own published values. Nevertheless, I'll used another bullet you picked in another test below.



Of course, what happens outside the convergence velocity zone affects the rest of the flight, but it can be calculated and for those of us who understand significance, useful conclusions can be made.



Of course actual bullets seldom follow either curve, but you are missing the point. In the convergence velocity zone there is only one curve. If a bullet doesn't follow it then it's not following either the G1 or G7 drag function. The topic is about how the G1 compares to the G7, and in the convergence velocity zone, they have the same curve.



Yes, but none of them can use this .308 cal. bullet, and about the heaviest bullet anyone makes that could be stuffed into 6.8mm Rem SPC is the 150 grain SGK.



I said I don't know of any long range shooter in their right mind who would waste their time on such a load. If Dave T was using the 240 SMK in a 30-378 Weatherby he might get it up to 2600 fps or so. Maybe you could use that for long range hunting, but that's different than launching a VLD type bullet at 2000 fps.



Thing is, you could lower the MV to 3200 or even 3000 and my example still works out better for the equal TOF BC.



Using the 0.308 210 gr SMK bullet you picked I ran the numbers to see how well Bryan's G7 BC of 0.316 matches Sierra's multiple G1 BC values. I also tested the equal TOF G7 BC to see how well it matches Sierra's multiple G1 BC values as compared to Bryan's G7 BC value.

I wanted to use the JBM site for this comparison, but it doesn't support multiple BC values. They have a Drag Function Array Conversion tool, but that's not the same thing. I used a program that does support multiple BC values in the way Sierra specifies to get both the drop and velocity values. Just so there's no question about accuracy, I also ran the G7 BC values on JBM and have included those in the graphic below.

I picked 3200 fps for the MV as that's about as fast as any standard caliber, such as the 30-378 Weatherby Mag, is going to push this 210 grain bullet. I took the calculations out to 2000 yards to get numbers well into Sierra's lower velocity range as that seems to be where you think there's a problem. I outputted the numbers to Excel to make it easier to compare both drop and velocity. The equal TOF G7 BC was calculated relative to Sierra's multiple G1 BC values from a MV of 3200 fps out to 1500 yards.

The drop values are in columns A through D and the velocity values are in columns F through I. The ballistics program's values are in rows 3 through 11 and the JBM values are in rows 16 through 24. The Sierra multiple BC value columns C and H have a yellow back ground. Bryan's G7 0.316 BC values are in the column just to the left of the Sierra column and the equal TOF G7 BC values are in the column just to the right of the Sierra column. The green background shows which values are closest to the Sierra values at the same range.



You can see how close the JBM values come to the ballistics program values, which gives confidence that the values for Sierra's multiple G1 BC are also accurate.

If we assume Sierra's multiple G1 BC values best matches their own bullet's drag characteristics, then it's clear that the equal TOF G7 BC value better matches that bullet then does the Bryan's G7 BC value for both drop and velocity for most ranges.

Below the drop and velocity values you'll see the results from the JBM Drag Function Array Conversion tool. Note that the tool uses the velocity zone conversion technique and comes up with the same value Bryan did by taking the simple average of the zone values. It's the same technique Bryan uses for evaluating his data, but the down range values show that the equal TOF conversion technique produces a BC that better matches Sierra's values. This is more evidence that measuring velocity and then TOF over long range produces more accurate values when measure BC, which was Ken's conclusion.



Of course JBM doesn't support Sierra's multiple BC values, so your TOF, and thus, your BC is off. The correct TOF is 2.186 at 1600 yards for an equal TOF G1 BC of 0.644.



The correct TOF is 1.532 at 950 yards for a G1 BC of 0.641. You got to use the right tool, and when dealing with Sierra's multiple BC values JBM is not it.

Being this 0.308 210 grain bullet will likely be launched at no more than 3000 fps I would use that for the MV and calculate the equal TOF BC to 1350 yards where velocity is near Mach 1.2. That value is a G1 BC of 0.641. Calculating from 2500 fps out to 950 yards I still get 0.641. That's the best single G1 BC for how this bullet will be used by most shooters.

As for G7, well I've already shown above that the equal TOF G7 value is more accurate then Bryan's value. Of course, I realize the differences are insignificant, but the question is, do you?

Long odds that something you wrote would be published in Shooting Times or some other publication, but if it were no one needs to check with you first to talk about what you wrote as long as they properly cite the source. That was done for Ken�s article. If you don�t think what MacLorry is saying is right then find a copy of Ken�s article and make a specific point. It�s not anyone else�s obligation to provide it for you.



From the dictionary: coefficient is a numerical constant that is a measure of a property of a substance. 6th grade math shows that a bullet with the same form factor as a standard has a value of 1. If it�s a perfect match it has a value for 1 at all velocities. Pick any velocities you want and plot them to get your curve. You can make the strawman argument that even the Y-axis intercepts the standard bullet�s curve if that makes you feel smart, but the context is VLD bullets. You only need look at the bullet drawings in Bryan�s book to see that every one with an i7 form factor close to 1 has a shape similar to the G7 standard bullet on the cover. What�s obvious seems to escape you in your attempt to disagree at all costs.

It�s pretty obvious your real goal is to disagree regardless of how dumb or out of contest your arguments are. I�ve ran all MacLorry�s numbers and more and what he�s saying is correct. My contention is that it doesn�t make much difference in the real world. Still, I�m going to buy Bryan�s second edition book because I think having an independent verification of other manufacturer�s BCs is important to long range shooting. I hope you can at least agree with that.

MacLorry - you sound like one of my old college professors - dry to the bone but with info that knocks the socks off. Looking at your G1 and G7 Drag Profile graph it came to me that two of Bryan�s velocity zones are completely within the Mach 1.7 to 2.6 range and a third velocity zone is about half in. All the data in the world within the Mach 1.7 to 2.6 range can�t tell you if a particular bullet better matches G1 or G7.

For some bullets like the DRT .308 200 grain all of Bryan�s data points are within that single line zone. You can guess from the shape of that bullet it will best match G7, but it�s a guess. Paging through I found the Sierra .338 250gr, Lapua .224 69gr, Hornady .243 100 gr, Hornady .243 105gr and Berger .243 108gr are some others with all their data in the Mach 1.7 to 2.6 range. Ouch!

You did say the graph had other implications � that�s an understatement.

Thanks, I think



Maybe I shouldn't have posted it, but you and JonA are the only ones paying any attention, so I don't think it will get any attention.

Whatever you intended to mean by that, I hate to burst your bubble but technical expertise means very little in getting something published in a gun magazine. Guys like Ken and Bryan are the exception, not the rule.

Now that you�ve added the second sentence, you have a correct statement. Congratulations. Unfortunately it does not apply to the bullet you said it did. The bullet I gave as an example has an i7 of .913 at 1500 fps and 1.051 at 3000 fps. You claimed it was a perfect match because at one particular velocity it has an i7 of close to 1.

Do you stand by your original statement? Would you expect a ballistics calculator using the G7 curve to give more accurate predictions with this bullet or a bullet with an i7 of exactly 1.30 over its entire velocity range? Is the lightbulb on yet? Did you happen to notice in Bryan�s plots that compare the data to the curves they are �scaled by the bullet�s form factor?� What do you think that means?


My goal is to teach correct information. What�s obvious is you have picked a side with your emotions. That�s unfortunate. Hopefully you�ll be able to see the data above through the red mist well enough to realize I gave correct information the first time and your emotional tirade was unwarranted.

His contention was the method outlined in his first post (not Sierra�s method to which he has now switched) gave a single G1 BC that was more accurate that what Berger gave for a bullet following the G7 curve. If you have really run all his numbers, as well as running them again at a different velocity as I suggested, you know that to be a false assertion.

It pains me to see the extent to which you�re �dug in,� now doing anything and everything in an attempt to win an argument. You�re jumping through hoops like a circus animal trying to sweep your errors under the rug, just so you can avoid being seen as �being wrong.�

It happens. It�s OK. It�s how we learn. No need to feel shame.

I�ll skip right to the important stuff, so only the truly interested need read the details.

You began this thread saying the G1 BC of .545 Berger provided for their 115 VLD was not accurate. You showed another method and came up with a G1 BC of .559. You accused them of using poor methodology to cause the error and due to that suspected their G7 BC�s may also be inaccurate.

Since I believe you�d rather recite the entire text of War and Peace than do any of the simple calculations which I told you to do and which prove you wrong, I have done the important one for you. Using the bullet you chose, using the exact same assumptions you used, using the exact same methodology you used, when launched at 2500 fps that bullet has an average G1 BC of .548 from the muzzle to Mach 1.2.

It is very clear to anybody who can read, that you were wrong. The large difference was caused not by Berger�s methodology, but by your choice of a very high muzzle velocity and the fundamental fact that one G1 number will only be correct at one velocity for this bullet. By now, this should be painfully obvious to everybody and I suspect, had you understood it in the first place, you never would have started this thread.

The number Berger uses is actually very close to this value. This value is the one that will be closer for the vast majority of users for that bullet. For the few shooting 378�s necked down to 6mm, your value will be closer.

That no single G1 value works for all applications with this bullet is most obviously not a fault of Berger�s methodology. It�s due to the fact the bullet follows a different curve.

That is all. Case closed. You started the thread for nothing. You were wrong. I know that is painful to admit (maybe try and prove yourself right using the Pejsa method now?) but it would be for the best.

For more details:


Yeah sure, by all means, just keep changing the inputs and methods until you get the answers you want. That�s how real science is done, right?

What in the hell are you doing using multiple BC values? Your first post, the reason you started this thread, was not to declare how accurate Sierra�s stepped BC method was. Quite the contrary. It may help confuse the issue so you can sweep the important stuff under the rug, but the rug can be lifted.

The only reason I used a Sierra bullet is because you asked for one as an example. Forget it and go back to the 115 Berger (or any other closely following the G7 curve) that you chose and the methodology you were advocating in the beginning of the thread.

You didn�t start this thread to prove using multiple G1 BC�s could give you accurate results. It is quite revealing that your final number-crunching comparison to prove you are correct did not contain the methodology you started the thread advocating as the best. That�s a concession without saying it outloud.

Again, more gibberish to cover up ballistics errors. You claimed a more accurate ballistics method. I have demonstrated it is less accurate.

What kind of shooters do you hang out with? Have you ever actually shot something at long range? I doubt there�s a single person who tries for first round hits at 1000 or beyond who will agree with you.

If I missed them, would I have highlighted them? You said them, you just failed to apply them. That�s why I highlighted them for you.

Isn�t it nice how things work out so well when you can simply make up data? From what basis do you �guess� the above? Again, your first claim word for word:

I gave you an example to illustrate your misunderstanding, a bullet with a i7 of near 1 and an i1 of near 0.5 that happens to follow the G1 curve better than the G7. And your response is if Bryan had kept shooting longer he would have gotten the opposite results? Very weak.

Your initial belief also suggests any bullet with an i7 closer to 1.0 than its i1 will follow the G7 curve better. This is untrue for a multitude of bullets. Bryan�s book is filled with examples.

It sure can. Most easily and accurately by using the drag curve that matches the bullet or using stepped G1 BC�s as Sierra does�neither of which did you advocate in your first post. Your first post allowed that divergence to give you a final G1 BC that will actually be less accurate than the one provided by Berger for most users. You claimed it would be more accurate than Berger�s number. You were wrong. Proven by your own methods.

Purposely missing the point.

Then you must not know many. You see, long range shooters like to shoot. A giant magnum that burns the barrel in less than 1000 rounds is great for taking some of the guesswork out of a single shot when hunting and provides a sure kill, but it�s a poor choice if you want to shoot thousands of rounds a year�or even a month as some here do. For that, most of us have other rifles that burn a lot less powder. With that comes much lower working velocity ranges.

Uhm, he was using it in the .308 Winchester at a much slower velocity than that. I believe he won a national trophy out to 1000 yds with it. Maybe you wouldn�t consider him a �real long range shooter� though.

So you think most users are using, what, 240 WBY�s instead of 6mm-378�s? Just how popular do you think rounds like that are compared with 243�s, 6mm Rem�s, etc?



I really do hope you can keep from bursting a vein and use this as a learning experience. You began a thread based upon a faulty premise. You were proved wrong. It�s OK, really. It happens.

In the end, you should now know why Berger�s G1 BC�s won�t necessarily match what you come up with if you chose a wildly different muzzle velocity. You should also understand the reason for the difference and how that has no bearing on the accuracy of the G7 numbers for bullets which follow the G7 curve relatively well. I hope you can put that to good use. Maybe try going out and actually shooting every now and then.

You�re busting a gut trying so hard to ignore the obvious and now you�re confusing BC with form factor. Back to basics for someone who thinks they�re teaching on this topic. Form factor is an indicator of how well a bullet�s shape matches the standard bullet�s shape; form as in shape. Take the time and look at the drawings in Bryan�s book and you�ll see that every one with a form factor close to 1 looks a lot like the G7 standard on the cover. Bryan makes the point about the G1 standard not being as close in SHAPE to modern VLD bullets as the G7 and that�s why the G7 is a better standard; are you saying he's wrong?



Wow, such an ego for a guy who has had his ass handed to him in nearly every post. You picked a Sierra bullet and listed out it�s BC/Vel values and then when MacLorry uses it with real numbers to prove you wrong you crap your pants and retreat back the original bullet. The only thing you�re teaching is how to dodge a lost point.



I read his original post again and it�s not his contention at all. His contention is that his method produced more accurate results for the G1 BC using the G7 as the reference. He infers from that FACT that his method (actually Ken Oehler�s method) would produce an even better G7 BC if applied when that bullet was tested. Nothing you�ve posted counters that argument because you were too engrossed on arguing that 5.8 inches is a big deal. With your head in the sand you didn�t realize you were not even arguing about the right thing � now that�s funny

It's no secret that if you pick a different MV the equal TOF BC may come out different. The real question is, is my original G1 BC a better value for this bullet than Berger's published G1 BC over a wide range of MV? If so, then my point about there being a better technique for calculating BCs is correct. Here are the numbers.



As you can see for a MV of 3000 fps the equal TOF G1 BC is more accurate as compared to the G7 BC than Berger's published G1 BC is out to 1300 yards even though velocity drops to 1.2 Mach at 1150 yards. For a MV of 2500 fps the TOF G1 BC is more accurate out to 700 yards and actually to 850 yards where the velocity drops to Mach 1.2. This is more evidence that the equal TOF technique is better for calculating BC values in the velocity range these VLD bullets will be used by most long range shooters.

That said, I made reference in my original post that Berger's number showed they were concerned with predicting their bullet's performance in the subsonic range. The numbers above demonstrate that as well.



For all your blustering you've only shown that my original post is correct even when extended down to a MV of 2500 fps.



I picked it because you offered the SMK as a counter example even taking the time to list out the multiple BC values. Using the bullet you picked I again demonstrated that the equal TOF value produces a more accurate G7 BC value than the one Bryan and JBM calculate using their velocity zone averaging technique.

Now you want to go back to the 115 Berger, which I did above and once again demonstrated that my original G1 BC is better even at the 2500 f/s MV.



No, but you offered up the SMK as a counter example. Neither of us has the original firing data for that bullet, so the only valid comparison for my G7 BC and the one Bryan and JBM calculate is Sierra's own BC values. What were you thinking would be the reference when you listed the multiple BC values?



You've said that a difference of 5.8 inches at 1500 yards is a significant error, but I'm not advocating using the equal TOF G1 BC in place of the Berger's G7 BC. The point is that the equal TOF G1 BC more accurately matches the G7 BC than Berger's published G1 BC. If you want to claim 5.8 inches is significant then the 21.8 inches from Bergers G1 BC is 3.7 times bigger difference. You call that less accurate?



Go look at Bryan's data points for the two bullets. You'll see the 115 Berger has a much wider velocity spread and more data points. The "guess" as you call it is based on understanding variability and confidence levels.



Just so there's no question later as to which bullet you now offer up, here's what you wrote before �the Sierra 107 Matchking has an average I7 of 0.993�should be a �perfect match,� eh? Wrong. It has over seven times the variation the Nosler has. It's actually a much better fit to the G1 curve than it is the G7 curve (even though its G1 I of 0.508 is quite a ways off from the �perfect� 1.0).� The Nosler you were referring is the Nosler 95 Partition.

We can use Sierra's multiple BC values to see if their .243 107 grain Matchking better follows the G7 or, as you claim, the G1 curve. No need to use JBM as it doesn't support multiple BC values and my prior post shows the program I'm using gets nearly the same values as JBM does.

The G1 BC values are 0.527 down to 2500 fps, 0.522 down to 1800 fps, 0.509 down to 1600 fps, and 0.495 below 1600 fps. Obviously, Sierra doesn't think their bullet matches G1 well or they wouldn't need to publish four BC values for it, but let's continue and see what the data says.

I'm going to use 3500 fps and take the data out far enough to get into the subsonic range to see which of Bryan's BC values best matches Sierra's own multiple BC. That way we get into velocities were there's a difference between G1 an G7 outside the profile convergence velocity zone. Bryan give this bullet a G7 BC of 0.262 and a G1 BC of 0.510. Here's the data out to 2000 yards.



Your contention that this bullet better match G1 than G7 is wrong. If you look at Bryan's data for this bullet you'll see that he has only 6 data points. Remember what I was saying about getting a different result with more data points, well this is a classic example. Also, most of Bryan's data is within the drag profile convergence velocity range where the G1 and G7 are indistinguishable. There's also a flaw in the way Bryan calculates Variation.

Like Bryan said, this bullet shouldn't mach the G1 standard better than the G7 standard, and it doesn't. The Form Factor theory is proven correct. If you weren't so busy trying to teach maybe you could learn something.

If you have any other bullets you want to offer as counter examples please do the work of posting the actual downrange numbers. It will save me time debunking your contentions.