Rate of twist


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bigcim
April 1, 2007, 12:06 PM
I have a 7mm rem mag with a 9.5 rate of twist and was wondering what grain of bullet or velocity were adequate for this twist rate

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Shoney
April 1, 2007, 12:47 PM
None of the twist/bullet-weight tables I have from barrel makers list the 9.5 twist, so dicide for yourself.
9 - 150 to 175
10- 140 to 160

My experience, with twist designations over several cartridges, using bullets of weights above and below those listed by barrel makers, is that "usually" a given twist will shoot acceptable groups to 200 yards . For accuracy further out, middle of the road weights are "generally" more accurate.

bigcim
April 1, 2007, 01:04 PM
so I probably shouldn't use a 120 grain for coyote or varmint

Jim Watson
April 1, 2007, 09:43 PM
No reason not to. The limit on bullet weight (actually length) versus rifling twist is an upper limit. Your rifle will surely stabilze a 120 gr bullet.

The only way to know if it will shoot them accurately enough for your varmints is to shoot the gun at a target.

Shoney
April 2, 2007, 06:57 PM
I agree with Jim, load em, and shoot em and see what you get.

EXAMPLE: I have a 6mmRem with a 10 twist, charts say 90 & 100 grain are ideal, and indeed, 100s, 90s, and 85HPBTs are all good to 600 yards. It gets 0.5" groups at 100yrds with 60 grain bullets, but the groups fall apart after 200. The 55 gr get 4100fps, with spectacular terminal results on prairie poodles, but accuracy is 1.0" at 100yards and your lucky to hit a bull in the butt with a banjo after that.

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