Thread: 308 twist rate

Originally Posted by Friwi

Ask @Wingman what was the twist rate of his 338br and what projectiles he was shooting subsonic and how they where flying.

My .338 Whispers ran 1-9" twist Shilen and trueflite barrels shooting 300gr SMKs and 300gr Berger hybrids at 1040fps MV.
They were still perfectly stable and grouping well with round holes at 1000y.
The team down in the butts nic named it the bumblebee as the bullets whizzed over with a deep buzz at sub speeds rather than the sharp crack they were used to.

I totally agree with @Friwi, all the best accuracy I have achieved with both subsonics and high velocity was a twist rate of "just enough" and faster twists barrels groups have always opened up.

Fast twist barrels in .308 were designed for use with the heaviest and longest jacketed bullets to run at subsonic speeds.
1-8" gives the best subsonic accuracy in .308 with the all the longest and heaviest bullets available such as the 240gr SMK.
1-7" is too fast and groups do suffer.
If you are using cast lead in a 1-7" you will also get a lot of bore leading which also destroys accuracy.
Lighter bullets in a fast twist don't nessisarally shoot slower than a slower twist will but do reach pressure faster which can in turn effect final achievable velocity.

The best twist for that cast 151gr HP at subsonic speeds is a 1-12" to 1-13". They are a short bullet with a blunt nose and base so dont require a fast twist barrel to stabilize them. The slower twist also combats bore leading.

Unless you intend on only shooting specialty machined copper expanding petal type subsonic projectiles and believe the marketing around the rotational energy of such bullet killing game any better than a subsonic soft lead cast HP or a tumbling after impact long 240gr SMK then dont bother with anything over 1-8" twist.

A 1-12" to 1-10" will actually shoot a wider range of subs and high velocitie bullets better than the 1-8" and 1-7".
You can shoot up to 220gr as subs as long as you run the round nose bullets.