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Old November 15, 2012, 02:58 PM   #32
Bart B.
Senior Member
Join Date: February 15, 2009
Posts: 6,318
For those who think a twist too fast won't impair accuracy may want to investigate the following.

When the Brits finally decided to do something about their .303 SMLE's not-so-great accuracy at long range, something had to be different. They already knew that the barrel whip properties of the SMLE let their cordite-loaded ammo's huge velocity spread compensate and made accuracy better past 500 yards. But the M1903 Springfield's out shot them handily with their 1:12 twist custom barrels and the new 172-gr. FMJBT machine gun bullet was used.

Finally, a smart Brit said the 1:10 twist in those SMLE's spun the 174-gr. bullets about perfect for decent accuracy leaving at 2500 fps, but the 150-gr. ones used later were spun too fast leaving at 2800 fps. He tried 1:11, 1:12 but finally settled on 1:13 twist barrels for the 150's leaving at 2800 fps. The Commonwealth's been using that for their fullbore medium and long range matches ever since with both the .303 Brit. and 7.62 NATO round. A 1:13 twist (and even 1:14) are now popular in Palma rifles shootng 150 to 155 grain bullets out at 2900 to 3100 fps. Faster twists start causing accuracy problems.

However, if you and your stuff can't shoot under 1/4 MOA at 100 yards or 3/4 MOA at 1000, you probably won't be able to tell the difference. For those who can, spinning bullets too fast matters. Best examples are the short range benchrest crowd shooting 22 and 24 caliber bullets; folks make tiny changes in charge weight as ambient temperatures change. They use twists just slow enough to stabilize the bullet and if it gets a few degrees cooler, the gotta add 1 or 2 tenths of a grain of powder to raise muzzle velocity just enough to increase the bullet's rpm's leaving the muzzle to stabilize it as it goes through thicker air. If a bullet's rpm rate didn't matter, they would not do it.

What about the .30BR round used in benchrest? Their 110 to 125 grain 30 caliber bullets leave at 2900 to 3000 fps. Best accuracy's with 1:16 to 1:18 twist barrels.

And yes, Weatherby did make lots of .300 Wby Mag's with 1:12 twist barrels.

Last edited by Bart B.; November 15, 2012 at 03:25 PM.
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