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Actual B.C. VS Claimed

 
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  #1  
Old 01-28-2008, 11:40 PM
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Actual B.C. VS Claimed

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
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Remington model 700 300 RUM LH 26" rem ss/blued receiver lam stock 215 Berger @3025/180 NAB @3300
Remington model 700 338 RUM LH 27" Broughton 5C 225NAB@3300 /300gr Berger@2830
Savage LH 22-250
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  #2  
Old 01-30-2008, 12:50 AM
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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
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  #3  
Old 01-30-2008, 03:46 PM
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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.
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Remington model 700 300 RUM LH 26" rem ss/blued receiver lam stock 215 Berger @3025/180 NAB @3300
Remington model 700 338 RUM LH 27" Broughton 5C 225NAB@3300 /300gr Berger@2830
Savage LH 22-250
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  #4  
Old 01-30-2008, 04:05 PM
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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 damn 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.
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  #5  
Old 01-30-2008, 06:19 PM
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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?
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  #6  
Old 01-30-2008, 07:31 PM
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Check this:

http://www.longrangehunting.com/foru...me-bc-s-16229/
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  #7  
Old 01-30-2008, 09:21 PM
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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..
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