Anyone running a 7in barrel on their ar15?

[JFettig]

from ar15barrels.com

The port size determines the pressures your system sees. Time under pressure is another factor too.

[Spook]

Jon, nice gas block, will it fit under a float tube and how much would you make them for? I've wanted to try a 30 luger with 208 Amax and that looks like it may be what I need.

[JFettig]

A tall gas block would not fit under a standard FF tube, it would fit under glacier guards though. The one pictured would fit under a FF tube. I have a similar one on my 300/221.

I don't think I'd be making them in my shop if I did some, I'd have to get a quote from work.

Spook, some guys are running large bullets in 7.62x25 TOK uppers. I haven't read much into it though. They run them from Pmags. AR15.com pistol cal and variants sections have a few posts in there.


Jon

[mak91]

I moved the gas port back 1 1/2 inches and made a gas tube by cutting down a rifle length tube and forming it to the shape I needed. Its running with a .100 size hole. So far its running with 110 - 150 - 240 grain bullets, the powders were lil gun, reloader #7 and h335 as these were the powders I had on hand. All but the 110 grain bullets locked the bolt back on an empty mag, it did feed the next round though. This was just a function test so I did not clock the rounds or check for accuracy. They were all subsonic though, I have shot some of these same loads out of my 10 inch barrel and they ran about 1000 fps. Barrel length is just over 7 inches and these were run without a suppressor.

[Spook]

mak, very cool ,how was the accuracy?

[JFettig]

Loooks pretty close to what I'm about to do soon with a barrel I have sitting here :)

[mak91]

Spook, Not sure on the accuracy yet as I did not have the opportunity to bench shoot this yet. I did shoot some 240 grain smk at point blank range (about 2 feet from the muzzle) through a cardboard target to see if the bullet was stabilized or not. The holes were nice and round so it looks like stability is not an issue with a barrel this short and the heavy weight bullets.

[Spook]

JFettig and mak, I wont be too surprised if these short barrels end up shooting moa out to 100yds.
Good on you guys for going where no whisper has gone before

[JFettig]

Hopefully testing tomorrow


-edit- shot flawlessly, hit the gas port diameter first try, locked back positively without too much gas.

Jon

[mak91]

No accuracy results yet but I did clock a few loads. Reloader #7 12 grains with a 150 grain bullet ran 880 -910 fps, the brass showed some slight marks from the extractor, makes me think I might have opened up the gas port a bit much for this powder or the port is to close to the chamber for the powders speed. Lil gun 7.8 grains with a 180 grain bullet ran at 934 - 967 fps brass looked ok. These are just the loads I had on hand. Does anyone know of powder that is a little faster than Lil gun (69) that will take up more volume by weight ? I have Accurate #9 but it seems to have a bit less volume by weight. I am looking for a powder to use with the 150 grain bullets that will take up more case volume. I don't like how much space is left in the case with the subsonic 150 grain bullets and these powders that I have.