SBR/Pistol R15 - what length barrel?

Post by **Vividia** » Sat Nov 15, 2014 12:24 pm

I am considering building an AR pistol, maybe later to turn into an SBR but that really isn't the ultimate goal just a maybe.

In doing the research I see barrel lengths from 7.5" to 10.5" in 1/2 inch increments. I am curious, for those who have put one together, how did you decide on a barrel length?

This will probably be a 300 blackout build, in case that matters. Might also put together a 556, but not immediately. Either way, I am thinking 1-7 twist.

Already have a Sig brace, enough spare lower parts to put one together, a couple of lowers (soon as I remember where I put them for safekeeping LOL), spare BCG &CH, so really don't have to buy much more to put it together. Just the upper parts.

Post by **Tyler** » Sat Nov 15, 2014 12:43 pm

I've read that 8-9" is ideal for 300blk. For 5.56 I've been happy with my 10.5-13" uppers. I may try out a 7.5 if I can find a really good deal on one.

Post by **Dustin** » Sat Nov 15, 2014 12:45 pm

If your going 300blk get the 8.5 barrel the round was designed for that barrel length. If you go the 5.56 route get the 10.5 get that round to run with a 7.5 barrel has some challenges with timing and the short gas system.

Post by **DDgunslinger** » Sat Nov 15, 2014 12:58 pm

Dustin wrote:If your going 300blk get the 8.5 barrel the round was designed for that barrel length. If you go the 5.56 route get the 10.5 get that round to run with a 7.5 barrel has some challenges with timing and the short gas system.

Run a pig tail gas tube from Phase 5 and gas issues are solved... just sayin

Post by **kokopelli** » Sat Nov 15, 2014 2:24 pm

DDgunslinger wrote:
Dustin wrote:If your going 300blk get the 8.5 barrel the round was designed for that barrel length. If you go the 5.56 route get the 10.5 get that round to run with a 7.5 barrel has some challenges with timing and the short gas system.
Run a pig tail gas tube from Phase 5 and gas issues are solved... just sayin

I built a 7.5 using a $100 AR Stoner barrel and carbine buffer, and it fed, fired and ejected even Wolf steel ammo without failure. -The key is to use a conical muzzle device like the Noveske Pig on it.

1fastmach1 · Post by **1fastmach1** » Sat Nov 15, 2014 3:12 pm

Dustin wrote:If your going 300blk get the 8.5 barrel the round was designed for that barrel length. If you go the 5.56 route get the 10.5 get that round to run with a 7.5 barrel has some challenges with timing and the short gas system.

My AR pistol has a 7.5" barrel and it runs like a top. I wasn't using a fancy brake when I first built it and it was great then. I put a pig on it a few months back and the only difference was the gun wouldn't shoot flames anymore and it dispersed the sound down range away from the shooter. My pig just shoot a huge grey cloud of smoke. I think the 7.5" is just a tad bit to short for flames with the pig. My original brake was a walking dead (link at the bottom) break and it shot brutal flames.

http://shop.redxarms.com/WALKING-DEAD-F ... 008423.htm

Post by **guncrank1** » Sat Nov 15, 2014 3:15 pm

If your pistol is under gassed , I would recommend to opening the gas port as no parts are required.

and if your want I have a 14.5 inch barrel (5.56) from PSA that I would be willing to cut down and rethread.

Post by **Niceguy** » Sat Nov 15, 2014 5:49 pm

Have have a 10.5" 5.56 upper from PSA and love it. It was cheap, runs great, looks decent and accurate. I think anything shorter is funny looking, just a personal preference though.

Post by **Jhud** » Mon Nov 17, 2014 9:54 am

I have a really nice 10.5" upper (Noveske) for sale. It is a 5.56 in 1/7 twist. Would be great for a pistol or SBR.

http://www.youtube.com/user/ssracer02 · Post by **ssracer** » Mon Nov 17, 2014 9:55 am

Mine has a 10.3" DD barrel. Runs perfect. Never dealt with .300blk though.

Post by **Niceguy** » Mon Nov 17, 2014 10:52 am

If you do the 300blk, keep us updated. I need to look into a 300 upper for my AR pistol also, I have a Octane45 on hold...

Post by **Wyldman** » Mon Nov 17, 2014 11:02 am

I found a 10.5" ss .300BLK barrel on SG for $97, shipped. Poking around in my parts box came up with enough parts to build another upper, sans barrel. I just ordered the barrel and an ejection port door marked ".300 AAC BLK", like the one I put on my rifle. I also found a pig tail gas tube & Lo-Pro gas block for cheap.

Guess who is building a pistol? My first AR pistol.

From the Wyldphone

Post by **guncrank1** » Mon Nov 17, 2014 12:25 pm

Wyldman wrote:I found a 10.5" ss .300BLK barrel on SG for $97, shipped. Poking around in my parts box came up with enough parts to build another upper, sans barrel. I just ordered the barrel and an ejection port door marked ".300 AAC BLK", like the one I put on my rifle. I also found a pig tail gas tube & Lo-Pro gas block for cheap.

Guess who is assembling a pistol? My first AR pistol.

From the Wyldphone

Fixed fir you

Post by **RecoilSensitive** » Mon Nov 17, 2014 2:19 pm

I have had pistols from 7.5-11.5

I liked the 11.5 best in 5.56 because it gives more velocity.

7.5 in 5.56 is a waste IMO other than range fun. (also many suppressor companies will not warranty cans on 7.5 uppers)

for CQB 10.5 or 10.3 is most common.

for 300blk i would do a 8.5-10.5 and add can

Post by **Vividia** » Wed Nov 26, 2014 3:16 pm

OK just ordered this

http://www.law-guns.com/ar-158300bblnitride.aspx

from Law-guns. Been reading good things bout it in the 300 BLK forums. Also made nearby in Indiana.

Post by **Next** » Tue Dec 02, 2014 8:19 pm

I hope to try out my new 7.5 barrel over Christmas. I think getting a KX3 / Pig type brake helps with the shorter barrels.

http://www.youtube.com/user/ssracer02 · Post by **ssracer** » Tue Dec 02, 2014 10:22 pm

Next wrote:I hope to try out my new 7.5 barrel over Christmas. I think getting a KX3 / Pig type brake helps with the shorter barrels.

it helps with the concussion to the shooter and those next to them if nothing else

Post by **Whootsinator** » Tue Dec 02, 2014 10:35 pm

The KX3 is over three inches long. If you'd have simply gone with a 10" barrel, which is the same length if not SHORTER than your 7.5"+KX3, the KX3 wouldn't be necessary.

Post by **Next** » Wed Dec 03, 2014 7:41 am

KX3 and similar devices helps to push the blast forward making it easier to shoot. The last 7.5 inch AR I had with standard birdcage felt like my face was getting sand blasted when shooting. Even with a 10 inch barrel I would still want a similar muzzle device. It also helps to drive the sound forward.

I bought the one below. It is only 2.25 inches.

http://www.kineti-tech.com/steel-muzzle ... ave-ports/

Post by **kokopelli** » Wed Dec 03, 2014 10:00 am

they also help develop the needed gas pressure to cycle the action reliably

Post by **Vividia** » Wed Dec 03, 2014 7:59 pm

I am considering putting the saker brake mount on it:

http://www.store.silencerco.com/collect ... zzle-brake

Post by **Next** » Mon Jan 05, 2015 9:26 am

Saturday I was able to get out to the range. I took both my 7.5 AR pistol with Kinetic Cone Brake and my 10.5 with Standard A2 Hider. Both were accurate at 50 yards using red dot optics. I didn't see any real difference with the two brakes as I would have thought. I even exchanged them on the two uppers, but didn't feel much of a difference. What did work for me was using a H2 buffer. Firing the pistols felt smoother with the heavier buffer.

I was able to hit bowling pins and pop cans at will up to 50-60 yards. Both cycled fine with PMC brass, wolf steel and Federal ammo. Was able to find the uppers complete for $350 with rail and bolt on ARFcom and quality was fine.

So in the end I didn't see much difference firing 7.5 or 10.5 inch barrels. Both are loud as heck and throw large fire balls.

Next wrote: I bought the one below. It is only 2.25 inches.

http://www.kineti-tech.com/steel-muzzle ... ave-ports/

Post by **jackalo626** » Mon Jan 05, 2015 11:28 am

Yes they are very loud!

Post by **ken6881** » Mon Jan 05, 2015 11:49 am

I put an 300 blackout 8.5" on mine and its quieter than my 9mm Taurus 99. Pistol gas tube and it cycled first time with Remington subsonic rounds.

samb. · Post by **samb.** » Mon Jan 05, 2015 4:47 pm

I have a law guns 8" 300blk and it won't cycle my subsonic reloads. Gonna eventually get a chronograph and work up a load that will cycle subsonic suppressed. Cycles the factory remington subsonic stuff and all my super stuff.

Kentucky Armory Club