Actual B.C. VS Claimed

[D.Camilleri]

I know this has probably been discussed before, but I am not finding the answers I want by searching. I am interested in 338 and 308 high bc hunting bullets. I just learned that Barnes has started adjusting their bc's for the tripple shock and it is WAY lower than what they used to claim. So how do other bullet makers advertised bc's compare? Is the Nosler Accubond 225 gr 338 really a .550? How about the Sierra game king 250 gr, is it really a .565? Why are the advertised bc's for Hornady's so low compared to others? Is it true that they are closer to real? How about the claimed bc's for 190 gr 308 Bergers? I am hoping to use good information that some of you already know before I spend a lot of time picking out my long range bullets. Thanks

 

[NesikaChad]

I'll toss in my two cents.

I think bullet manufacturers understand that its in their best interest to provide accurate/truthful data when it comes to bullets.

Potential litigation being one if applied in a LE or even DOD type applications.

The other is that we have the capacity to verify it if we choose to do so. The gun and shooting community is very fickle and the masses will gather for a lynchin just as quick as they will for an awards ceremony.

Nothing more exotic than a chronograph and some ballistic software is needed to verify what manufacturers are publishing.

I personally don't think its anything to get overly concerned about.

If Barnes changed their published data then I would have to assume that they discovered an error in the information being passed or they changed the bullet's design somehow. What other explanation is their?

Either way, they win and we win. Honesty is always the best policy.

Good luck

 

[D.Camilleri]

According to Barnes, they are now checking the data at 300 yards after actually shooting the bullets. They used to check the bullets at 100 yards. They claim that other bullet makers rely on computer models based on the bullet design that are not backed up by actual field tests. I am just reporting what I read to see what other opinions are out there.

 

[milanuk]

Did they go into how they do the testing? If just going by drop figures, I wouldn't feel 300yds is far enough to see a significant difference unless you have very solid zero data, and a very good gun/rest. If they are going by chrono numbers... well 300yds is about as far as some folks might want to go due to a (legitimate) fear of hitting the screens on the second (downrange) chrono. Even then, the spacing needs to be pretty **** precise, and the chronos calibrated to each other, etc. etc.

Where the factory B.C.s get all hosed up is that they use G1 numbers... which aren't necessarily the most accurate ballistics model to use for modern HPBT or polymer tipped boat tail bullets. It's reasonably accurate for shorter ranges (600yds and in), or if you 'fudge' the numbers a bit like Sierra does w/ their multiple-BC practice, you can get it acceptably close. G5 or G7 BCs would be more accurate, but they aren't near as impressive (high) up front and most ballistics software looks for a G1 number by default - if they can even accept other G# BCs.

 

[Natty Bumpo]

I'm no engineer, but if I recall correctly, doesn't B.C. change with velocity and other factors; so the values published represent something of an average?

 

[royinidaho]

Check this:

http://www.longrangehunting.com/forums/f19/roy-i-have-some-bc-s-16229/

 

[Mikecr]

BC does change with velocity and air density.
This because the drag curves we use don't match our bullets, and we don't shoot under 'standard conditions'.

With some newer software, coefficients can be calibrated to allow accurate field results under any condition using one BC.
This is somewhat like reverse engineering for a best internal drag curve. RADAR would help here a great deal, but few bullet makers test to this level. And neither do most shooters..

 

[D.Camilleri]

My reason for starting this thread is aimed at predicting terminal performance in long range hunting situations. If a bullet is advertised as having a high bc but really doesn't, then the choice that is made might not be the best for long range clean kills. Like many people, I might get caught up in how well bullets do on paper based on velocity and bc. Lower bc's loose velocity faster and with the velocity loss comes lower retained enery. I like to pick loads that have maximum retained energy and accuracy for best long range terminal performance.

 

[NesikaChad]

My reason for starting this thread is aimed at predicting terminal performance in long range hunting situations. If a bullet is advertised as having a high bc but really doesn't, then the choice that is made might not be the best for long range clean kills. Like many people, I might get caught up in how well bullets do on paper based on velocity and bc. Lower bc's loose velocity faster and with the velocity loss comes lower retained enery. I like to pick loads that have maximum retained energy and accuracy for best long range terminal performance.

In that case, go buy some big ol hams or roasts and blast em from the distances you want to shoot at.

Mmmmmmmm, smell the carnage. . .

 

[D.Camilleri]

I was thinking more on the lines of some soon to be delisted elk eating wolves!

 

[Top Cat]

The entire concept of BC is based on mathematical "models" that are themselves based on real-world observations...in other words...a long time ago somebody threw a bunch of various shaped rocks downrange and took notes on what happened to them.

All of the current ballistic computers are based on those notes, and the degree of exactitude expressed therein should not be taken literally, as it is not an exact science. At best, a model represents a scientific attempt towards a "best guess".

The testing performed to arive at a BC number is very rudimentary, as the equipment necessary to measure BC in a more finite way is generally well beyond the resources of the small arms community. Even if that advanced analysis were to be undertaken, the figures still get plugged back into some mathematical model or another...and then we are right back to making guesses.

Now, some of these guesses can turn out to be pretty close, and often are, which is lucky for us, the shooter, because usually all we are really interested in is how many elevation/windage clicks are necessary to get on target... and that is fortunate.

The best way to figure all that out is to do some range testing and try to find out where the bullets are landing most of the time...just like those rock throwers of long ago. The range method really works, and once you plug some real world drop data back into a ballistic computer, you should be good to go for other environments as well, but only for that particular rifle...that load...and that bullet.

That is because factors related to the individual rifle, like barrel harmonics, site height, and a few others, will also effect drop data, and the resultant BC number.

So in the process of doing your own real-world ballistic testing you can use reverse logic to come up with a BC number that gives drop performance that is close to what the programs predict for the bullet you are using.

If the program you use is pretty close to your real world results, then that is the best BC number to use, regardless of what the manufacturers have published...a bit more testing will determine that. That does not necessarily mean that the BC figure you come up with is will be the correct one for your buddy using a different rifle rig.

Basically, the manufacturers BC rating is really only there for comparison purposes, and just like the EPA mileage ratings manufacturers assign to cars...your mileage may vary!

TC