Home Forums Hunting & Shooting Long Range Hunting 30 Cal BC Test

Certainly not all-inclusive but I figured some would find the info useful. I measured in about the most accurate way possible for anybody without a million dollar underground range and I'm confident in the results. Of course I wasn't shooting 10 shot strings which would have upped the confidence level (some bullets were more consistent than others) but that'll have to wait until somebody else is buying me barrels. <img src="/ubbthreads/images/graemlins/wink.gif" alt="" /> Anyway, for what it's worth:



Calibrating the Oehlers:



The 206 yd target/205 yd chronograph, with spotter target to the lower left:



The view:

Interesting Information. Thanks for sharing it.

HBB

What is the difference between Standard ICAO and Standard Metro BC's?

Doug~RR

Regardless of if the calculations are "correct" or not, this is the way its supposed to be, real world data, same set of conditions, same gun, same day etc.... This means you can tell which bullet has the best coefficient, regardless of if that number is off .050 or not.

Very nicely done. I've always wanted to do the same since I have a private range with permanent benches at 100,200,300 and 600. Though I'd be scared to shoot to 600 without a trap to protect the works... Soon to be almost 1000 if things work right.

Jeff

Jon, Thanks for sharing the results of your work. Very useful to me. <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />

Very interesting data. You will no doubt be deluged with requests to test further bullets.

One thing I am interested in. Notice the crooked meplat on your 210 Sierra MatchKing photo. They now sell meplat uniforming devices, which should make the BCs more uniform but, I suspect, reduce them a little. I wonder if this in fact occurs.

Doug, they're just two different set of "Standard Conditions" at sea level that you should use as in ballistics calculations. ICAO is 29.92 pressure, 59 degrees F, 0% Humidity while Metro is 29.53, 59 degrees and 78%. There isn't much difference, Sierra uses Metro, Nosler uses ICAO, etc. So if you were using Sierra's Infinity program you'd want to use the Metro numbers because that's what it expects you to use.... Hopefully I didn't confuse too many people by listing both. <img src="/ubbthreads/images/graemlins/wink.gif" alt="" />

Thanks for the comments, Jeff. I agree that's the best part of a test like this--same day, rifle, chrony setup, etc. Sort of like a "bullet drag race." <img src="/ubbthreads/images/graemlins/laugh.gif" alt="" /> Of course I do try my best to set everything up correctly and do the environmental corrections as accurately as possible so the results are repeatable (and meaningful for others) so I don't have to test the same bullets over and over again. Of the four I tested before, the biggest difference between the tests was .016 with the others being .011, .004 and .001. So I figure I don't need to test them again except for control purposes to validate future tests.

Five of the eight tested to within about 5% of their manufacturer's rating which I figure is pretty good with differing barrels, test velocities, etc. Of the other three, two don't have a current manufacturer's rating so there's nothing to compare with.

Indy, yes that isn't uncommon with Matchkings--though they did test out pretty consistently anyway. I haven't tested uniforming but others have and it generally does reduce the BC slightly but improve its consistency. Of course there are other sources of inconsistency that are harder to see with the naked eye.

Jon,
Thanks for the explanation, and posting your results which I saved. I had done a quick google search and looked in an old Sierra reloading manual about the BC's ,and came up empty.

Doug~RR

That was quite the effort! Thanks for the information. Don't suppose you want to share which company's BC matched your data?

I remembere Rick Jamison did this BC test years ago. The most amazing thing to me was the BC would change based on different muzzle velocities. If I remember correctly he showed that individual rifles showed a BC starting low building up to a peak and then tapering off as the velocity was increased. Unfortunately we cannot try to figure out which velocity is best for each rifle. My personal conclusions after reading that article was that it is amazing we manage to hit animals at long range. The more I know the more I am humbled by the facts.

Sure. The XLC is still advertised at .552 by Barnes but they've since admitted their old methods of measuring/rating BCs left much to be desired. So I don't feel it's fair to hold them to that anymore. If they keep making it very long they'll probably re-test it as they have the TSX.

The GS Custom used to be rated at .650 (God only knows where that number came from <img src="/ubbthreads/images/graemlins/crazy.gif" alt="" /> ) but a recent check shows Gerard has taken all the BC data down from the page with the note:

So it's only fair to consider that bullet unrated at the moment. Maybe Gerard will put out some realistic accurate BC's the way Barnes has the second time around.

Of the remaining six, the TSX and MRX were a bit low but not too far off from Barnes' rating (I don't know if their advertised ratings are ICAO or Metro). "Close enough" for most purposes anyway.

The Scirocco beat its advertised number by a bit as it always does. That's one sleek bullet.

The AccuBond was a bit lower than advertised, but pretty close.

The 210 SMK was a bit higher than advertised. That isn't too surprising since their own data shows BC going up with velocity and I measured at a higher velocity than I expect they did.

The only one that was off "significantly" was the 240 SMK. That was disappointing to me since I like that bullet so much, but the Oehlers don't lie. I wasn't all that surprised since that's about exactly what I had measured it at last time but I was hoping the 1:9 twist barrel would show an improvement this time. It didn't, it's just not there. The story my test doesn't tell however, is that its less efficient more pudgy shape is supposed to hold onto its BC better as velocity drops compared with the 210. Even so, if I didn't already have bigger and better things on the way, I may look at switching to the 210. I have no idea how its terminal performance would be though, I'd have to test. I know the 240 flat kills stuff.

Thanks for mentioning the company names. I talked with TY at Barnes yesterday. He said they are retesting their bullet's BC using Ohler equipment. They are shooting at 300 yds.

Thanks to JonA for a nice experiment presented well.

It has galled me for years that we calculate exterior ballistics to four digits of precision using a drag funtion that might fit an individual bullet to within five or ten percent and BCs measured over short distances.

We use the G1 drag function for most references because of a "gentlemen's agreement" that it is better to have only one drag function as standard instead of using many different yardsticks. These same gentlemen agree that G1 doesn't fit all bullets, and that in fact that it doesn't fit any bullet exactly. Their sane philosophy is that BCs based on G1 are close enough for rough comparisons, but actual downrange performance must be determined by actual firing.

The apparent change in BC as velocity changes is simply an indication that the bullet's actual drag function does not fit the the accepted G1 model. Sierra has chosen the logical expedient of quoting different BC's at different velocities; this may well be the most practical solution.

The measurement of BCs is not easy. For years we have told folks that getting BC measurements is at least ten times as hard a getting velocity measurements. For BC, we must measure the velocity lost, and to measure the velocity lost we must accurately measure the velocity at each end. Any time you are looking at the difference between large and independently measured numbers, the large numbers must be measured very accurately, or the accuracy of the difference is questionable. Actual measurement of BCs to an accuracy of better than five percent requires good equipment and a lot of work. Speer's old numbers that quoted a BC of 0.29 instead of the modern convention of 0.291 were a true admission to reality.

For many years, the military has avoided this problem by not using the BC concept except for very coarse estimates. They measure the individual drag characteristics of each projectile as the basis of their "firing tables". This is simply beyond the means of individual shooters or even bullet makers.

The best we can do is to actually measure drop, velocity, or time-of-flight at several ranges that would preferably include the maximum range of interest. If we "fudge" any good exterior ballistics program to fit our firing data from the longest range, the program outputs will closely fit the actual data from the intermediate ranges. The secret is that we're using the program to "interpolate" between our measured data instead of using the program to "extrapolate" short-range data to longer ranges.

We're working on it.

KenO

Jon,

Thanks for the effort, it is good info.

Sierra measures it's bullets BCs over 4 or 5 different velocity boundries. Bullets BCs often decrease as they slow. The 210 Sierra is an excellent example. It's BC falls off rapidly and at around 2000 fps it's BC drops to something like .375. This makes the 210 Sierra a dog, and drifts about 10" more at 1000 yds than the 190, 200, and 220 grainers when fired from the same case at best velocities. I have about 400 I need to get rid of.

It would be a lot of work, but it would also be interesting to see what the Bcs will measure at the lower velocities, say what you get at 1000 yds.

Thanks for the kind words, Dr. Oehler.

I agree on the G1 thing--especially for all the VLD-style bullets out there these days. In Sierra's defense, they have stated in the past that most of theirs fit the G1 curve the best and their BC data backs this up somewhat (G1 BC's not changing much over the velocity range listed). But that was before they made the 210 which is quite a departure for them and naturally should be closer to the G5 or G7. But that's another story--I hope they're scratching their heads as much as I am about their results for that thing (I'd hate to be the only one <img src="/ubbthreads/images/graemlins/wink.gif" alt="" /> ). I sure would love bullets to come with their own measured drag curves...but I'd like to win the lottery too. <img src="/ubbthreads/images/graemlins/frown.gif" alt="" />

Blaine,

If I used the 210's for hunting, the most likely ranges for me would keep them at a pretty decent velocity (high altitude and I can launch them fast) so performance should be pretty good over my desired range even if Sierra's ratings are accurate.

On that subject, I wouldn't say the 210 is a good example of how a bullet's G1 BC changes with velocity. I'd say it's a horrible example. It's so far off from being representative of how most pointed boattails act it's more like an aberration. Sierra's numbers for this thing are so far in left field I don't know what to make of them.

One wouldn't expect this bullet to follow the G1 curve as closely as most of their others do, but this thing doesn't come close to any of the curves--at least the way Sierra rates it. G5, G7, etc, it's way, way off from all of them. Not plus or minus a few percent throughout the velocity range as you would expect any bullet to be, but off 40%, 50%, 60%....! Somethin' just ain't right here.

I roughly sketched in what the portion of the drag curve, based upon their ratings, for that bullet would look like:



So either Sierra has invented a bullet that flies like no other projectile known to man (which would be amazing since it looks virtually identical to other 210s which are proven performers at long range) or their testing/rating of the BCs at various velocities was flawed.

I won't claim to know what the deal is. There may be something about its shape which escapes my eye that makes it so unique. I have a few theories on what could have gone wrong in testing, but I'd want to know more details on how they tested it before I put my money on that. If derived from Doppler data, well OK, nevermind then. If not.... If I wanted to use these at 1000 and beyond, I'd do quite a bit of my own testing before discounting them out of hand based upon those published BC's.

Anyway, while quite interesting to me, I'm not worried enough about it that I'll likely do much further testing to unravel the mystery since I won't be using any of these bullets for much longer. But I will love to hear results of anybody testing them at an extreme range where it should be pretty clear if they're working better than advertised or not.

Jon,

Really cool, thanks for sharing.

I am starting to look at BCs differently. Given Sierra is the only company that actually measures BCs over multipe velocity boundaries, my take is their numbers have just shown us what VLDs really do at long range. Based on how the Berger 210s shot in my rifle, I'd say Sierra is hitting closer to the mark with their BCs for their 210 than Berger is with the BCs for his 210. Obviously I'd need to do more testing at 1K to verify my "take", but I am becoming suspicious of the predictive model used to calc BCs for these VLDs.

I discounted the 210 SMKs them because they shot like crap in my rifle.

Unfortunately, I am no longer motivated to fuss with any VLDs because the 220 SMK is posting ES of 11 fps, is shooting the small group of matches (4.000" best), and is winning matches overall. Further, it has an excellent BC which has been reflected at the 1K target.

If it wasn't going so well with the 220 SMK I'd be trying 210 JLKs. It would be fun to set up a chrono at the muzzle AND at 1000 yds.

That could be Blaine. I'm just thinking out loud here, I don't know all the answers.

I would be more inclined to believe that if Sierra was the first to actually test a VLD style bullet. But of course, they are not. Even disregarding the Military, companies like LRB, SOE, etc have been doing the doppler thing with bullets of "VLD-ULD type shapes" for quite some time. If bullets shaped like that opened up parachutes (picture little parachutes like those on the back of really fast drag racing cars) progressively as they lost velocity as Sierra's data would indicate for this bullet, I think it would be pretty well known by now. And I don't think these guys would choose bullets shaped like that for rounds they expect to perform well beyond 1000 yds--even more than twice that distance, where the differences would become very clear.

Frankly I think it more likely to be exposing shortcomings in Sierra's testing methods. Measuring via doppler at actual ranges is going to be so much more accurate than reduced loads fired over 150 yds from a marginal twist (they had to recommend an 11 twist since that's what the competition recommends, so maybe they felt they had to use that twist while testing?) where yaw, coning effect, etc could greatly influence the results that I'm going to say I'll need to test for myself before I put that much faith in Sierra's data for this bullet. Then again, maybe it really is correct for this particular bullet. Maybe there's just something "wrong" with the design I don't see.

Like I said, I'm just thinking outloud and welcome more thinking out loud on the subject to point out anything I've missed. That's how I learn. <img src="/ubbthreads/images/graemlins/wink.gif" alt="" />

A 1000 yd chronograph test like I did above would give some insight. While the difference in trajectory from a "somewhat" constant BC and Sierra's data wouldn't be much, even at 1000 yds from my rifle, the velocity at the far end would tell an interesting story. I'd need to make some sort of sheild for the chronograph though, or I have the feeling I'd be calling up Dr. O. yet again for more replacement parts..... <img src="/ubbthreads/images/graemlins/laugh.gif" alt="" />

JonA,
I would be interested in what you think after reading this.
http://www.pejsa.com/articles.htm
Thanks for the great test.
dave <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />

I ain't JonA but that fella Pejsa makes my head hurt. <img src="/ubbthreads/images/graemlins/grin.gif" alt="" />

Jon, a very well presented piece, and thanks for that.<img src="/ubbthreads/images/graemlins/cool.gif" alt="" /> <img src="/ubbthreads/images/graemlins/cool.gif" alt="" />

Now I have a question for you or Dr. Oehler regarding variations of BC due to nonconformity to the G1 Function, and the apparent reduction of BC as velocity increases. Robert McCoy's book "Modern Exterior Ballistics" is quite explicit that for numerous forms, to include Boat Tail Spitzers, Cd diminishes as Mach increases. There are some specific drag curve examples of this up to velocities as high as Mach 6 IIRC. I'm not saying anybody is wrong one way or another but it seems my mind is short circuted on the matter...I'm seeing this as a conflict...mebbe not? Can somebody shed some light on the matter? <img src="/ubbthreads/images/graemlins/confused.gif" alt="" />

One additional question: ISA...did the specs on that change within the last 30 years? Seem to recall that humidity was once part of the standard though nobody references that from what Google shows... <img src="/ubbthreads/images/graemlins/confused.gif" alt="" />