Tips on building a SBR AR-15

[captain clay]

I've decided to build up a short barreled .223 AR, but have been told to expect reliability issues.
I was told using a 9mm buffer is a must because its heavier is there any other mods I should do?
My choice of uppers is limited to either a rock river armory 7 inch (kitty kat) or a 10.5 inch version.
I am leaning towards the 7 inch version, would it be fun to shoot or a regrettable investment?
Anyhow I'll follow all the laws and pay my $200 tax.
any input would be appreciated.

 

[captain clay]

Would a fixed stock with its longer buffer tube help at all?

 

[RockyMtnTactical]

Yeah, you'd want a 9mm buffer most likely...

I would go with a 10.5 or 11.5" barrel personally. Just because I'd want the velocity. Shorter the barrel, the less velocity, and the less reliability (in general).

I wouldn't worry about a fixed stock.. and as long as you are going with something that is "longer", a longer barrel would be more preferable (for reasons stated above). Otherwise, leave it with a CAR buffer tube.

An AR SBR would be fun. It would be a decent CQB weapon, and it would even be pretty accurate out to a decent range (100-200 yards easily).

However, I feel that a 16" AR is a better overall weapon. Less reliability issues. Much better velocity. Better long range accuracy/ballistics. No "paperwork" with the ATF (plus you save yourself $200).

 

[wdlsguy]

SBR FAQ at ar15.com.

 

[captain clay]

Ok so a heavier buffer is a must then any other modifications required, I just read about failures to eject and how a stronger extractor spring is sometimes required.

 

[wdlsguy]

My 11.5" AR runs fine with a regular carbine buffer.

 

[Zak Smith]

A properly built 10.5-14.5" SBR should run with a regular carbine buffer. The 10.5's are pretty sorted out. It's a lot harder to make 7's run well.

 

[captain clay]

Would heavier grain bullets help aid in reliability?

 

[Zak Smith]

I don't have any data but my guess would be that if loaded to the same peak pressure, they would make the problem worse since they would present higher pressure at the port than 55gr.

 

[captain clay]

Thanks for all the input from all of you.

 

[swingset]

Having owned quite a few, I won't personally go under an 11.5" again. That extra inch gives a good bit of velocity and reliability without losing hardly any length.

 

[ny32182]

I just finished that one up with a 10.5" upper and normal carbine "H" buffer. It functioned fine for the 48 rounds that I put through it last weekend. I think it might be cycling a little quicker than my 16", but not excessively so. Might switch to an H2 buffer if I end up putting a can on there.

10.5" is as short as I would feel comfortable going. Shorter than that, and you get into funky proprietary AR-pistol gas systems (this upper uses a normal carbine gas system with the exception of a slightly oversized port), and you'd also lose any semblance of adequate ballistic performance from milspec ammo (muzzle velocity on this 10.5 is already practically *at* the good fragmentation threshold, making it a 50 meter gun at most for optimal ballistic performance with milspec ammo... that can be extended with specialty ammo though).

 

[dscottw88]

THREAD RESURRECTION!

So I wanna go with a 10.5" upper but was wondering if I could fit Mid length rails on the rifle and go with no front sight post. Anyone have a pic of this setup?

 

[Zak Smith]

This thread should not have been resurrected. Please open a new thread on the new topic.