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Rifles, Bullets, Barrels & Ballistics Applied Ballistics


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How is this possible?

 
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  #1  
Old 10-02-2011, 02:34 PM
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How is this possible?

I was visiting the Accurate Shooter site and came across info on the 30BR round.
The parent case is either 6mm or7mmBR. The case is necked up for 30 caliber bullets.
Here's the part I don't understand.....they're claiming 2900 to 3000 fps with the 30BR using33 Gr. of H- 4198 powder. For a comparable load with the 7mmBR, the maximum velocity is 2685 using 28.5Gr. of H-4198. (both rounds shooting a 115Gr.bullet). So how do they get the extra fps?
I'm no ballistician or math whiz....would appreciate someone out there to explain this to me.Thanks in advance.
Chas
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  #2  
Old 10-02-2011, 03:48 PM
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Re: How is this possible?

Well, being that the 7br is .284" diameter bullet and the 30br is .308 and they are both likely flat base bullets so 2 simple reasons are 30 cal has a larger base to push against and a much shorter bearing surface, which leads to less pressure in the 30 cal with equal powder charges, so you can use more powder and get more speed.
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Old 10-02-2011, 04:55 PM
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Re: How is this possible?

Faster powder will work better due to the larger throat diameter too.

Tank
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Old 10-02-2011, 05:12 PM
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Re: How is this possible?

+1 Backwoods
And 4.5gr more powder..
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Old 10-02-2011, 05:50 PM
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Re: How is this possible?

Thanks for the explanation.
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  #6  
Old 10-02-2011, 05:51 PM
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Re: How is this possible?

I think they are using a pretty fast twist barrel also.
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  #7  
Old 10-02-2011, 06:07 PM
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Re: How is this possible?

They state a 1:14 or 1:15 twist. That will work up to about a 125grn bullet.

Tank
__________________
Matthew 7:13-14
"Enter through the narrow gate. For wide is the gate and broad is the road that leads to destruction, and many enter through it. [14] But small is the gate and narrow the road that leads to life, and only a few find it.

If you find your self in a fair fight, your tactics suck!- Marine 1st Sergeant Jim Ryfinger

Friends don't let friends develop canonitis!-chucknbach

arguing over the internet is like the special Olympics....even if you win, you are still...special!
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