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Caliber relationship to bc

 
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Old 08-24-2008, 10:39 AM
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Caliber relationship to bc

Would you agree with the idea that the larger the caliber the easier it is to build a high bc bullet? I grew up thinking 7mm bullets were higher bc than anything else without thinking why. Now we are starting to see some higher bc bullets in 338 and 375.

A good example of caliber relationship to bc is provided by Hornady's Amax line:

224 80g bc=0.453
243 105g bc=0.500
264 140g bc=0.550
284 162g bc=0.625
308 208g bc=0.648
510 750g bc=1.050

You'll never see a bc=1.05 bullet in 224 caliber save maybe a two pointed pencil solid, or will you?

I'm thinking now the small calibers are limited mainly by the fast twist needed to launch long bullets and the larger calibers, say 375, are limited mainly by heavy bullet weight. It's hard to launch a 400 g bullet really fast.

What do you think?

Last edited by Varminator 911; 08-24-2008 at 10:43 AM.
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Old 08-24-2008, 11:38 AM
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Re: Caliber relationship to bc

You can fool around with this BC calculator and get some interesting results.

Precision Ballistic Coefficient Estimator
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Old 08-24-2008, 12:10 PM
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Re: Caliber relationship to bc

30 caliber has higher BC bullets than the one that you listed. the 240 SMK is .711
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Old 08-24-2008, 01:43 PM
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Re: Caliber relationship to bc

It's never been difficult to 'build' High BC bullets in any cal. The challenge is to build bullets that perform well across the board.
Highest BC bullets generally fail this test, even though offering an edge (in very limited circumstances).

Sierra SMK bullets for example are not very high in BC compared to others in cal and weight. But just about anyone can get their gun shooting well with them.
The same cannot be said of higher BC bullet brands(like Berger VLDs).

And then there are the close range benchrest shooters. Their not concerned at all about BC. They need fast flat base bullets from slower twists which release truer from the muzzle.

Just some thoughts..
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Old 08-24-2008, 03:18 PM
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Re: Caliber relationship to bc

Quote:
Originally Posted by Varminator 911 View Post
I'm thinking now the small calibers are limited mainly by the fast twist needed to launch long bullets and the larger calibers, say 375, are limited mainly by heavy bullet weight.
Yes. The advantage larger calibers have is that higher SD bullets can be made less "long and skinny" than smaller calibers. To match the SD of a 338 cal 300 SMK, for instance, a .224 would need to be 132 grains. Using similar construction, this would basically be as long as a pencil and require a silly twist rate to stabilize, one that would likely rip the bullet apart while any old 1:10 works for the 300 SMK.

So if you stick a small bullet in a "Honey I Blew Up the Bullet" machine to take it up to a larger caliber while keeping everything else proportional, you end up with a bullet that has a higher BC. This is because the SD goes up--the cross sectional area goes up with the square of the increase in size, weight goes up with the cube. And being the same shape, the CD or Form factor will remain basically equal.
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