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B.C./Drop Report--MUST READ&COMMENT

 
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  #1  
Old 02-02-2010, 08:38 AM
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B.C./Drop Report--MUST READ&COMMENT

With a great interest in BC on the board these days I figure I would include a report I've recently discovered. THIS IS NOT A JOKE! IT IS REAL!
After a bid of dicussion I will post a link to the full report. You may find it interesting.

Here is an excerpt taken from the report on B.C. with some drop data included.
Please comment and give me a BC for this bullet according to the data.
Unfortunately the author did not give the exact environmental conditions.

Here it is:

"How long the bullet yaws depends on the bullet itself, the rifling twist and even the crown of
the barrel. Some barrel/bullet/crown combinations result in a much shorter period of bullet yaw,
something apparently impossible to predict. When it does happen, however,the bullet will shoot alot flatter than indicated in any computer model. A fine example is my .257 weatherby Vanguard Sporter.This rifle shoots 100-grain Barnes Triple Shock XBullets into tiny groups--and also shoots them much flatter than the bullet's listed BC indicates. The muzzle velocity of the rifle's best handload is right around 3,500 fps and when sighted in 2" high at 100yards, the little bullet is still around an inch high at 300yards when shot at typical western elevations of 4,000'-5,000' above sea level, and only 5" low at 400yards.This is alot flatter than any ballistic program suggests, even when higher elevation is "plugged" into the equation."

So guys:

A. Is the writer of this report claiming an impossible BC to purposely mislead the public for the purpose of selling more 100 grain Barnes Triple Shock XBullets ?

B. Is he a novice and just not familiar with the method of properly zeroing a rifle and testing drops?

C. Is he simply stating the results he got with his rifle with no other adjenda

OR:

D. Other

PLEASE CHIME IN!

Last edited by RockZ; 02-02-2010 at 10:26 AM. Reason: spelling typos
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  #2  
Old 02-02-2010, 09:10 AM
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Location: South Central PA
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Re: B.C./Drop Report--MUST READ&COMMENT

well after running the numbers im on my way to buy all these bullets i can find. Ok not really but barnes list a BC of.397 for these bullets and from what i come up with a .900 BC is what you would need and it still would not match up perfectly. It would be 2.2 inches high at 100 1.1 inches high at 300 and 4.5 inches low at 400. Now i know the BC can be off a little bit but i think it is usually higher than the actual BC not way lower. I also could not tell you of the choices you provided which one is the most correct.

Now if the guy cant read a tape measure or a pair of calipers then it might be pretty close with a bc of .400 2.6 high at 100 will give you 1.3 high at 300 and 5.6 low at 400 which this may be more the case because he may have just been guessing and not actually taking a measurement.
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Old 02-02-2010, 10:05 AM
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Posts: 5,192
Re: B.C./Drop Report--MUST READ&COMMENT

It could be a case of "TALL TAILS"or simply the wrong velocity numbers.

Some barrels shoot faster than others buy up to 100 ft/sec and this could skew
the numbers.

Not all high pressure loads show typical pressure signs.

I think it is all of the above.(Wrong velocity,poor measurements,high pressure load,
tall tails or maybe the wrong yardage numbers.

It is hard to say how he came up with those numbers .

Over the years I have heard many tall tails of how flat someones rifle shot and normally
It was over estimating the yardage (A 500yard shot that was really under 300yards).

I my self witnessed this with a well respected guide after making a good 600yrd + shot
that he swore to all was over 900 yards. (Who was I to correct him in front of everyone)
But I knew because I ranged it several times before and after the shot.(We did not have
range finders back then) and there was some guessing and stepping off the distance.

So I would say Don't Believe every thing you hear !

J E CUSTOM
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Old 02-02-2010, 12:12 PM
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Location: South of Canada and North of Wyoming
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Re: B.C./Drop Report--MUST READ&COMMENT

These drops really aren't that far off the mark. If I run a .5 BC with an MV of 3500 @ 5000' elevation zeroed @ 320 yds I get

100 - +2.6, 300 - +1.0, 400 - -5.6

with a BC of .4 I get

100 - +2.8, 300 - +1.0, 400 - - 6.0

with a BC .4 and an MV of 3700 I get

100 - +2.4, 300 - +0.9, 400, - -5.3

Not a whole lot of difference between those and all very close to the bullets actual published BC.

The data provided is much too general and just slightest mis reading at those short distances can result in huge calculated BC swings. Chrony's are not all that reliable and how consistant are the loads being used? There are a lot of possible varibles that could greatly affect a calculated BC at those short distances including maybe the possibility of pitch and yaw.

Will be interested in reading the rest of the article but I think it will mostly be anecdotal based on info provided so far.

-Mark
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  #5  
Old 02-02-2010, 12:15 PM
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Join Date: Apr 2009
Location: western Oregon
Posts: 120
Re: B.C./Drop Report--MUST READ&COMMENT

So the author is claiming that his particular gun/barrel/twist/crown combo consistently causes this particular Barnes bullet to "yaw" in a tail down, meplat up attitude? Causing it to maintain a flatter trajectory because it is "flying," achieving lift from said yaw? Every single time??

I suppose it could be possible,...

But I'm going to remain the skeptic about it.

Now if a barrel maker comes along and claims (with documented proof) that they can engineer/build barrels that do this every time I might,...

Naw, I still don't think so!
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  #6  
Old 02-02-2010, 12:16 PM
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Location: SW Montana
Posts: 4,257
Re: B.C./Drop Report--MUST READ&COMMENT

Playing with JBM I don't have to change BC to get those numbers, just changing the scope hight will get it. I shoot with a scope hight of 2.2 so that is what I compared to.

300yrd 0 in, 400yrds -7.3 in

Now change the scope hight to 3in

300yrd 1.6in, 400yrd -4.9 in

I'm just getting the hang of ballistic calculators but you can really screw something up if your inputs aren't quite correct, and you then think you shooting a miricle bullet.
I start looking for where I screwed up on my inputs when my drops don't come reasonably close to the predicted trajectory, so far I have found the problem to be me and my data not some miracle BC.
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  #7  
Old 02-02-2010, 12:21 PM
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Location: South of Canada and North of Wyoming
Posts: 5,954
Re: B.C./Drop Report--MUST READ&COMMENT

Bigngreen, scope hieght is another big consideration. when I played with that it dramatically changed things..

Bottomline, I dont see anything all that unusual in the data provided.
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