Gunsmithing Resolved: BEST TWIST RATE FOR A 16” 308 BARREL?

[Gas]

Hi gents.
I’m thinking to do my “final built”. One of the specs is, the barrel has to be 16”. Wanted to know what’s the best twist rate for it. I’m mostly going to shoot 175gr m118lr or maybe the 168gr counterpart.
Thanks
Gas

 

[Badfinger]

I know several guys still doing well with the 1:10 in bolt guns.

 

[Gas]

I know several guys still doing well with the 1:10 in bolt guns.

Mine is a gas gun but that shouldn’t matter as far as the twist rate goes. I’m more worried about stability of the bullet with a short barrel and if the twist rate needs to be more egressive. 1/10 is pretty much is the standard I’m gonna go with unless somebody changes my mind.

 

[briang7511]

1-10 is common, probably the best overall. i have a 18inch, 1-12tw and handles 178 bthp with no issues. Berger has a twist rate calculator that may help with any indecision you have.

 

[Gas]

1-10 is common, probably the best overall. i have a 18inch, 1-12tw and handles 178 bthp with no issues. Berger has a twist rate calculator that may help with any indecision you have.

Prefect, I’ll check out the calculator. Thank you.

 

[Aaros143]

I've run a lot of 308 out of a 16" 1/10 twist. All of it suppressed. Never had an issue. And that includes a few 5 gallon buckets of M118LR.

 

[Lowlight]

10

 

[Gas]

1/10 it is then. That’s mostly I’ve heard, I’ll get the order done in 1/10 then.
Thank you all gents, you’ve helped me a lot.

 

[kirkbriderd]

1/10 it is then. That’s mostly I’ve heard, I’ll get the order done in 1/10 then.
Thank you all gents, you’ve helped me a lot.

Its not the barrel length, but the bullet length that determines the twist rate.

 

[Lowlight]

Its not the barrel length, but the bullet length that determines the twist rate.

this is not necessarily true, you can over spin a bullet if you reduce the velocity, increase both and you risk destroying the bullet.

a shorter barrel can be spun faster if one so desired

 

[Gas]

Its not the barrel length, but the bullet length that determines the twist rate.

Although you have a point as far as the bullet length and weight, that is not the only factor.

Case in point: If you’ve seen bullets tumbling and key-holing out of those homemade AKS74U’s that’s because people just cut the barrel meanwhile the twist rate is the same 200mm. The ak74 has 200mm twist rate, however for the shorter barrel AKS74U it was necessary to change the twist rate to 160mm because at the low velocity out of a shorter barrel the rotation per 200mm was not enough to stabilize the bullet in the air.

As @lowlight said the slower going projectile can typically handle more rpm. As the bullet is making X amount of rotations per Given distance, at a lower velocity it also takes more time for the projectile to cover that distance, and the slower the velocity, the less air resistance.
Hope that was of help. Thank you.

 

[kirkbriderd]

this is not necessarily true, you can over spin a bullet if you reduce the velocity, increase both and you risk destroying the bullet.

a shorter barrel can be spun faster if one so desired

The bore twist rate is a distance measurement. Velocity is time-distance measurement. Thus a bullet revolves one revolution say every 11" and 2945 times in a second (rps) at 2700 fps. Versus 2836 rps at 2600 fps.

 

[Gas]

The bore twist rate is a distance measurement. Velocity is time-distance measurement. Thus a bullet revolves one revolution say every 11" and 2945 times in a second (rps) at 2700 fps. Versus 2836 rps at 2600 fps.

I’m pretty sure he knows that
One think you’re not taking into account is the difference in the air resistance with different bullet velocities. To generalize, that’s the main reason heavy projectiles use heavier twist rate to stabilize on the trajectory.