Simply stated, that is not a true statement. Not even close. Do you have a link to Ken�s article? I really hope he didn�t say that. I think it�s more likely you have read that into something he did say.
My statement is true and the numbers prove it within the stated limits of supersonic velocities. Right now the Shooting Times website is being revamped and they are not offering their back issues on-line, but you can go to a good library and look up Ken Oehler's July, 2007 Shooting Times article yourself.
You are misunderstanding the significance of the form factor. It is simply a value, not a description of how �good a match� a particular bullet is to a particular drag curve.
As for the use of form factor, I used it to select the candidate bullet. I wanted one that closely matched G7 of those bullets that Berger publishes G7 BC values for, and as you found out yourself, it's a good match. If the G7 trajectory for that bullet can be closely matched using a G1 BC, then it replicates what Ken did in his article with a G1, G5, and a G7 BC.
What Ken didn't have in 2007 was a bullet for which a manufacture published the G7 BC and which was shown to be nearly an exact form factor match to G7. I tested Ken's conclusions using such a bullet and found that his conclusions were still valid and did so using the JBM site so that anyone reading my post could check the numbers.
Maybe Bryan read Ken's article or maybe he noticed the same thing himself, which is that while the magnitude of drag depends a great deal on bullet shape at supersonic velocities, the profile (curve of the drag coefficient line on a graph) doesn't change significantly due to bullet shape at supersonic velocities. That's why Brian says "From about 2000 fps and faster, the drag curve of the typical long range bullet and the G1 standard do not change very much." in his book
Applied Ballistics For Long Range Shooting (1st edition page 18).
Though in this case, that bullet is a pretty decent match--because it�s FF changes less than 1% over the range of velocity (per Bryan�s measurements), not because it happens to be close to 1.0.
All standard bullets have a form factor of 1.0, and thus, an actual bullet with a form factor of 1.0 is an exact match. More specifically, form factor is the actual bullet's drag coefficient divided by the standard bullet's drag coefficient at a given velocity. Simple math proves that a value of 1.0 represents a perfect match to a given standard bullet at a given velocity.
BC is an actual bullet's sectional density divided by its form factor. Whatever average form factor was used for Beger's #24530 can be calculated by dividing its sectional density by its BC. Thus, for #24530 the G7 form factor is 0.9972. A value so close to 1.0 is a strong predictor of how well #24530 matches the G7 form factor at all velocities. Knowing this, I didn't need access to the source data used to calculate #24530's G7 BC.
What makes you think this is insignificant? That�s two clicks! Unless you�re aiming at something big, it�s very likely a complete miss. Hitting something at 1500 yds is hard enough, why would you purposely put the center of your theoretical perfect group all the way onto the edge of the target by using less accurate data?
You may not think a difference of 5.8 inches is insignificant at 1500 yards, but as I pointed out, it represents a change in MV of just 14 f/s. Yes, it's nearly two scope clicks, but unlike bullets, optics are not subject to the same degree of cumulative errors over range, and thus, the change in MV is a better way to equate such an error. In practical terms, the consistency of a load's MV establishes what is or is not a significant error at a given range. By 1,500 yards 5.8 inches becomes insignificant.
Even at the closer ranges your data above begins to diverge by several inches at ranges many here shoot all the time. This will be noticed.
Once again, these "several inches" are insignificant compared to those caused by normal random changes in MV.
This is certainly where some of this is coming from. Of course you could just as easily say, �Since I won�t be shooting the bullets as far as they�ll go accurately I can get away with using less accurate data.� I don�t understand why you�d argue we should as well, much less that bullet companies should aspire to only provide data that�s �good enough� to Mach 1.2 when many of their customers use them below that by the thousands. You could also say you never shoot beyond 200 yds so bullet companies really don�t need to provide BC�s at all.
I'm basing Mach 1.2 on what others in this forum stated in my topic "Determining a load's maximum range". The consensus is that shooters are well aware of the inaccuracies induced at transonic velocities and consider a load's maximum range to be where its velocity drops below Mach 1.2, with some wanting to say above Mach 1.6.
Seriously though, while the errors are not as great above that, they are there. If you have more accurate data, why not use it? Why say bullet companies should be less accurate?
Like I stated, assuming the G7 BC trajectory is correct Beger's published G1 BC is less accurate than the one I calculated using Ken's technique. That suggests their technique for calculating BCs is not as accurate as Ken's technique, and thus, even their G7 value could be off. This assumes we care about predicting the trajectory of #24530 over the velocity range shooters will actually use this bullet for.
Secondly, especially when talking about LR hunting rifles, 1000 yds isn�t anywhere close to far enough to be around 1.2 for many bullets and rifles. A 1000 yd TOF measurement wouldn�t tell you much. All the interesting stuff happens much after that with the big guns. If you think the logistics of doing this at 1000 are hard, try 2000 yds. Good luck with that.
The same applies to the techniques manufactures now use. Sierra has a 300 meter underground range, which I think is the longest in the industry. As soon as you go outdoors you can't control the conditions nor can you even know them without an expensive instrumented range. As I said, this is likely why no manufacture is doing this, and while impractical, there's value in raising awareness of a potentially better approach to calculating BCs.
What makes you think the two are not directly related? You�re obviously not talking about some obscure theoretical case in which a bullet flies in a particular way which allows it to generate its own lift. For the context of this discussion, if you know one metric you know the other. The better you know it, the better you know both.
Bullet shapes that decelerate at different rates drop at different rates�with respect to yardage, not time obviously. If you fudge the numbers so they match up at one particular long range, you will be off in the mid ranges. Then if you change anything, such as MV or the atmosphere, you aren�t even matched up at the same long range you were the first time.
Of course they are related, but the numbers I posted show that you can't take the simple average of several BC values for a number of velocity ranges and combine them the way nature does to come up with the true BC. The flaw is in the math being used. Ken's technique lets nature combine the numbers perfectly over a large velocity range. Nature's averaging results in a TOF. Use the velocity and the TOF over a long range and you'll get a BC value that better matches the bullet's trajectory for the velocity range the bullet is intended to be used for. I posted example numbers and you can go to the JBM site and try them yourself for different MVs and ranges, I did. Ken's technique holds up well for any velocity #24530 was intended for. Same for every VLD bullet I tried.
The holy grail of accuracy�a Doppler radar, gives you the exact drag profile of the bullet yard to yard but that�s just not doable for even many bullet makers, much less users. Short of that about the best we have are measurements such as Bryan�s, which can be many times better than a single measurement as they can actually tell you about the drag curve of the bullet�not just give you some single average value.
The problem is the same as for measure BC over long range; once you go outside you can't control or even measure all the conditions that effect bullet flight. For example, Doppler radar can't see wind in clear air, so you can only measure bullet velocity relative to the radar antenna and only along a straight line from the bullet to the antenna. Being a bullet's trajectory is parabolic, the error of the measured velocity increases over range and can't account for the effects of wind at any range past the muzzle or where it's being measured independently.
What you end up with from Doppler testing is velocity vs. time data. If you use the velocity zone drag averaging technique to calculate BC you'll introduce the same error we see in current published data.
Lost River used Doppler data to calculate their BC values and Lapua went one step beyond by reportedly incorporating the Doppler data into their ballistics calculator program rather than dummying it down into a single BC value. Curious about that, I ran their downrange velocity numbers and used them to calculated BC values that I then used to predict downrange velocity numbers using JBM. The difference in the downrange results between Doppler based numbers and BC based numbers were insignificant. Go try it yourself.
Using your proposed method, a bullet with a �good G7 shape� will have vastly different average G1 BC�s if measured from the muzzle to subsonic when launched at 3500 fps than when launched at 2000 fps. Are you also proposing manufacturers should give average G1 BC�s for each muzzle velocity?
Of course, and that's why it only works for supersonic velocities. You know, the velocities anyone using a VLD bullet would care about.
Measuring such a bullet as you propose at one velocity would give horribly inaccurate results for somebody using it at the other velocity. You make no distinction.
Not true for supersonic velocities from muzzle to the target, which is the distinction I made, it produces better trajectory predictions than current published BCs.
But if the bullet was one Bryan had measured, a guy has all he needs to get very good results at either velocity.
But the equal TOF BC gives better results over the velocity range such VLD bullets are intended for, and that's the point.
Or if a Sierra, the velocity ranges listed with the BC�s would do the same.
Have you tired comparing Sierra's multiple BC results with a measured G7 BC and then compared it to a properly calculated equal TOF BC? If not then you have no bases for your claim. If you have, post your numbers. I would like to see just how close Sierra is getting to matching a G7 trajectory with their technique.
You seem to be wanting to fix something that isn�t broken (at least with those two companies)--or even break something that�s been fixed.
I'm just raising awareness to the limitations in the current system. Some find that annoying, but that's how progress is made.
Doing what you suggest would be a giant step backward. Now for some companies that provide no data or uselessly inaccurate data it would be a step forward, but you were specifically saying it would be better than the way Berger advertises or Bryan measures in his book. That�s just not the case.
I demonstrated with actual numbers that the G1 equal TOF BC better matches the trajectory than Berger's published G1 BC relative to the G7 BC for a bullet that's a near perfect G7 form factor match over the velocity range that bullet will be used for. In doing so I've demonstrated a limitation in technique Berger and others are using assuming that hitting the target is the goal of publishing BCs. Anyone can check the numbers for themselves so it's not just my opinion.
