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Different shape boattails effect on BC

 
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  #1  
Old 11-02-2013, 02:21 PM
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Join Date: Nov 2012
Location: Copper Basin, Alaska
Posts: 767
Different shape boattails effect on BC

How much effect do the different shape boattails have on ballistic coeffeficency??
Do rebated boattails have a greater effect than a straight taper. ?
Thank you.
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  #2  
Old 11-02-2013, 05:11 PM
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Join Date: Aug 2003
Location: NC, oceanfront
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Re: Different shape boattails effect on BC

There are sweet spots to boat tail angle.
An example with angle changes to 6mm 105 Lapua,while holding same weight:
BTA= angle
BCbyED= ICAO G1 BC @ 3Kfps by angle changing end diameter
BCbyBTL= ICAO G1 BC @ 3Kfps by angle changing boat tail length

BTA BCbyED BCbyBTL
4 0.485 0.513
5 0.490 0.506
6 0.493 0.500
7 0.495 0.495
8 0.495 0.490
9 0.494 0.485
10 0.492 0.481
11 0.489 0.477
12 0.486 0.474
(do know how to space)
There there can be an angle with the best overall balance in origin. Lapua chose 7deg.
The trend holds but shapes differently at other velocities and air densities.

I can't calculate rebated boat tail results. They do not increase BC over linear angles, and if I remember right Litz found they did not hurt BC much if any either.
The benefit they seek is in accuracy from cleaner release at the muzzle.
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  #3  
Old 11-02-2013, 09:35 PM
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Join Date: Nov 2012
Location: Copper Basin, Alaska
Posts: 767
Re: Different shape boattails effect on BC

OK. Thanks. . My goal is to find the best combination for my fur bullet. . As most predators are taken at 300 yards or less I want a bullet that will be stabil at close range but also be stable at long range. So I'm kinda looking for a unicorn. . Its easy to find target or big game bullets but not so easy to find what I'm after.
So, I'm hoping to get some educating.
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