.300BLK twist rate?

[Strykervet]

I'm getting a .300BLK bbl. made. I am having it cut 14.5" with a carbine length gas system. It will be suppressed with an AAC SDN6.

I plan on using bullet weights from 110 to 220 or 240 grains. I'd like to optimize the twist rate for heavier bullets and I know how to do that using the formula, but I would think that twist would be the worst for the 110 (and may not stabilize it at all?).

What experiences do those of you that have the .300BLK have? What twist rate do you have and do you experience unstable bullet flight? With what bullet weights? If you have the twist optimized for heavy bullets, how do your lighter ones fare? How light can you go before you get problems with accuracy and stability?

Just looking for as much information as I can get, and thanks!

 

[Z-Michigan]

I expect the project lead (RSilvers) will chime in before long. All I've read is that 1/8" twist stabilizes the heavier subsonic bullets (at least to 220gr SMK) and has no significant drawbacks for lighter supersonic bullets down to the 110gr range. This is based on reading, not direct experience.

Not sure if carbine length gas will be ideal with a 14.5" barrel. It is used on the 16" barrels but even there is not the only choice and you can find 16" barrels with pistol length gas setups. Because of the relatively large bore and small case capacity the barrel pressure tails off rapidly and you can practically do the opposite of what makes sense on a 5.56 barrel.

 

[LiquidTension]

I'm not sure if a carbine length gas system will cycle subsonic rounds. I think most of them are set up with pistol length systems.

 

[Z-Michigan]

Carbine gas in a 16" is supposed to work if the subsonic loads use certain powders that generate relatively more gas volume. But I believe it's on the edge, and my hunch is that going to 14.5" might go past the edge.

 

[LiquidTension]

You may be right. I'm sure Robert will be along shortly to sort it all out.

 

[Strykervet]

Okay, so now what about the gas system? I looked online and came to the conclusion this should work based on what AAC has. Just to be safe, I emailed Satern to ask them to cut it to 16" if they haven't cut it yet (doubt it) and told them to just do whatever they needed to do to get it to run reliable. I understand that it is supposed to be most reliable subsonic and supersonic using a carbine length but you have to use a suppressor. Then the pistol length was better for subsonic with no suppressor. I can't recall where I read this at.

 

[Z-Michigan]

I think you'll get a definitive answer if you wait a bit for Robert Silvers to comment. He is fairly active here, and more active at Silencer Talk (he is site admin there), and to some extent at m4carbine.net and quarterbore forums.

I've read the same as what you're saying, but all I've read is about either 16" barrels or much shorter barrels, I haven't seen anything about a 14.5".

 

[Strykervet]

Yeah, that would be great.

 

[Ranb]

A 1-8 twist will stablize a 240 grain .308 bullet at 900 fps and higher with any length barrel. I have a 300 whisper with a 1-8 twist that shoots 125 to 240 grain bullets very well. It does not like 150 FMJ surplus bullets though.

I have a 1-10 twist 308 bolt gun that stabilizes 220 RN just fine also.

Ranb