Need a little help determining twist for SBR

[este]

Ok,

So I want to build an AR in 300... that's about all I know for certain

I have an AR lower that I plan on making an SBR anyhow and a suppressor I want to build on Form1. In this case I think I want a 300 upper with an 8-10" barrel for subsonics mostly. That's the problem, "mostly".

Everything I've found says that 220-240 out of an Ar w/ a 10" barrel should be right around 1:8". But what if I want to shoot lighter bullets ? Can I get away shooting 125 or 150 supersonic out of that ? I understand that I won't get the highest possible velocity due to the barrel being short but I just want to occasionally shoot super, most of the time I'd be reloading subsonics.

So... I'm trying to figure out what is the best for me. I can make concessions like no shooting 240gr in it allows me to shoot lighter stuff, or going with 1:10 if it will be better all-round etc. I'm pretty sold on an adjustable pistol gas block or one with a three setting system.

Advice ?

[320pf]

Originally Posted by este

Ok,

So I want to build an AR in 300... that's about all I know for certain

I have an AR lower that I plan on making an SBR anyhow and a suppressor I want to build on Form1. In this case I think I want a 300 upper with an 8-10" barrel for subsonics mostly. That's the problem, "mostly".

Everything I've found says that 220-240 out of an Ar w/ a 10" barrel should be right around 1:8". But what if I want to shoot lighter bullets ? Can I get away shooting 125 or 150 supersonic out of that ? I understand that I won't get the highest possible velocity due to the barrel being short but I just want to occasionally shoot super, most of the time I'd be reloading subsonics.

So... I'm trying to figure out what is the best for me. I can make concessions like no shooting 240gr in it allows me to shoot lighter stuff, or going with 1:10 if it will be better all-round etc. I'm pretty sold on an adjustable pistol gas block or one with a three setting system.

Advice ?

I shoot 1:8 barrels for sub-sonics and super sonic loads... No problem. You will deficiently want the gas port in the pistol position. I get about 2250 pfs with 125 gr bullets and 2050 with 150 gr bullets from a 16-inch barrel. With a 10-inch barrel you will lose about 200 fps. Sierra Bullets and Hornaday have published reloading data shot from 10-in barrels TC pistols.

I hope this helps and good luck with your porject

320pf

[este]

Well that's ideal if an 8" 1:8" will work for 125-240gr, but can it be that easy?

What is the down side? If 1:8 will do it, the why do people go 1:10?

Would the accuracy of an 8" 1:8 suck with a 125gr at supersonic? Or do I just not get the same potential energy as say a 16" ?

Does too fast of a twist do something I don't realize?

[JFettig]

I have a 10.5" 1:8, I shoot 125gr TNT primarily out of mine. I get ~MOA accuracy and 2000-2100fps.

I have also shot 220gr subs with no problems.

Jon

[este]

Sweet! That's what I want then.

I'll just add it to my SBRed lower and roll! I just an upper now :\

Whose parts do you use Jon ? (I'm browsing your site by the way, some day we'll have to talk cnc)

[JFettig]

I got my barrel from tp555 who is a member here. I sent him my blank and he finished the barrel.
I'm just using a lo-pro upper and dpms bolt carrier with it and a custom adjustable gas block I made for myself.

Jon