Why 1:12 for USMC but 1:10 for Suppressor?

[PraetorianArms]

I tried searching for this but came up short.

The general advice found here at the hide is that for a 308 the 1:10 is superior for shooting suppressed or heavier rounds for stabilization.

I'm not doubting but if its superior why does the USMC run a 1:12 twist rate on the M40A5, or GAP use a 1:11.25 for the HRT? I would assume both these organizations run suppressed frequently.

Can someone pass some knowledge this way?

 

[PLeighton]

Re: Why 1:12 for USMC but 1:10 for Suppressor?

1:12 is best for 175 SMK

Subsonic suppressed needs at least 1:10 to stabilize.

 

[redneckbmxer24]

Re: Why 1:12 for USMC but 1:10 for Suppressor?

USMC has been shooting M118LR for quite some time now which is 175gr and 1:12 is fine for that. Unless they change to a heavier bullet I don't see them changing something that works and has been working great.

1:11 is the most common twist I see used on aftermarket barrels, it gives a wider range of bullets it will stabilize over the 1:12 but its not a huge difference.

1:10 is only superior for suppressed shooting because its much better for subsonic loads. Other than subs it gives no advantage over suppressed shooting unless of course you want to shoot even heavier bullets (like 190gr+). With a 1:11 or 1:12 twist 150-170gr is about all you're going to be able to stabilize for subsonic shooting, MAYBE 180gr but thats chancing an expensive can if you tumble one. With a 1:10 you can stabilize up to 200-220gr bullets which are ideal for a subsonic 308 if you ask me. Some people shoot even heavier cast bullets but you're going to want a 1:9 or even 1:8 for those.

 

[PraetorianArms]

Re: Why 1:12 for USMC but 1:10 for Suppressor?

I guess the corps and the FBI arent too worried about running subsonic ammo.

 

[Jethro3898]

Re: Why 1:12 for USMC but 1:10 for Suppressor?

Interesting question.....I have another.

Say I have a .308 with a 1:12 twist 24" barrel.
If I got a can for it one day, would I not be able to shoot subsonic loads through it accurately?

From the above responses, I should be able to shoot standard loads though my rifle suppressed, but I might have trouble with subsonic loads....correct?

 

[methos12]

Re: Why 1:12 for USMC but 1:10 for Suppressor?

I'm also curious to learn more about this. The .308 I have in my sig is a 5R 1:11.25 and I'm getting a TBAC for it. I was planning to mostly run regular 175gr SMK loads through it but for fun I also wanted to run 190gr subsonic. Should I even bother trying subsonic?

 

[SSSamurai]

Re: Why 1:12 for USMC but 1:10 for Suppressor?

You can still shoot subsonic ammo, you just might have to find a lighter bullet to use. Hornady 150gr RN is an option if you can't stabilize the heavier stuff. BTW, RN bullets are easier to stabilize since they're shorter. And test everything thoroughly before you put the can on, make sure they're not tumbling!

 

[OutlawTen5]

Re: Why 1:12 for USMC but 1:10 for Suppressor?

I shoot 175gr & 190gr subs thru a GAP built 24" 1/11.25tw using my TBAC 30-P without any accuracy issues at all (from 10 yards to 350 yards). I have not yet tried 200-220gr bullets.

 

[totenkopf]

Re: Why 1:12 for USMC but 1:10 for Suppressor?

Yes, interesting for sure. I'm going to load some tungsten powdered bullets which may make a barrel twist change unnecessary to fire true subsonically. I can moodify the bullet length and weight much easier. Even at a subsonic speed, the terminals will be better.

Mark