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Lighter Bullets, Fast Twists and Ballistic Coefficients

 
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  #1  
Old 12-30-2001, 06:41 AM
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Join Date: Nov 2001
Location: Sydney Australia
Posts: 40
Lighter Bullets, Fast Twists and Ballistic Coefficients

Firstly, shooting kangaroos at long range is somewhat different to your long shooting. In our case we take them as they come and ranges could vary from 100 yards to way way out. Thus we are not focused on a single animal.

So a 270 might be used with 100 grain bullets or a 375 with 270 grain bullets or a 300 Winchester with 150s.

Now to my question or query.

As we all know standard twists for the above caliber/bullet combinations are way faster than necessary.

My "observations" have been that spitzers do not seem to give (it varies) the advantages over blunt bullets that they should.

My only theory is that the quick twist results in the spitzers getting a bit sideways and hence having a lot of ballistic coefficient wiped off.

I remember a few years ago testing a 300 Winchester bench gun with 1 in 10 twist at 500 yards with 125 Sierra, 150 Hornady and 180 Hornady. What stood out was the windrift. The 125s and 150s were quite similar and the drift was far more than the 180s, as compared to what ballistic tables would suggest.

Mike
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  #2  
Old 12-30-2001, 08:29 AM
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Join Date: May 2001
Location: Pennsylvania
Posts: 1,757
Re: Lighter Bullets, Fast Twists and Ballistic Coefficients

Hello Mike

For Longrange hunting, the twist that is RECOMMENDED for the heavier and higher BC is the one I use.

In the big 22s --22/284---22/6mm IMP Etc. 8 twist and 80 gr match bullets.

6 mm such as 6/06--6/284--6/Ackley--8 twist and 107 gr to 115gr match bullets.

6.5/284--6.5/06--6.5 Gibbs--264 Mag --6.5/300 Weatherby--Etc---8 twist and 140 to 155 gr MK bullets.

300 win, 300 Weatherby, really any 30 cal imp with a large case design-- 10 twist with bullets up to 220 gr match. Some barrel makers say a 9 twist for the 240 gr but, the 10 twist works just fine.

My 338/416 Imp has a 10 twist and I use the 300 gr bullet.

I would hunt with the SAME bullet I would use at longrange even if a close shot presented itself.

Of course I recommend a Match King and the heavier ones in the caliber you are shooting.
The higest BC in the MK, I have found to work the best in any caliber I shoot..

Good luck and Good shooting.
Darryl Cassel
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Darryl Cassel
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  #3  
Old 01-05-2002, 07:17 PM
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Join Date: Jan 2002
Posts: 2
Re: Lighter Bullets, Fast Twists and Ballistic Coefficients

Remember that some published BSs are not quite accurate, and mostly overstated. This is because they are determined mathematically form the shape of the bullet, not by firing it and measuring the drop in velociey at different ranges. Also, the BC changes with vbelocity.

Some are understated. for instance, Sierra says the BC of their 80 grain .224 Match King is .424, but some knowledgeable people have measured it and gotten values up to .484.
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