Making an AR pistol.

Don’t cut the barrel, replace it. On a carbine it most likely has a gas system designed for a carbine. Going pistol length barrel with carbine gas system is a recipe for erratic feeding issues.

OR, better yet, just build a pistol from scratch. By the time that you swap barrels, swap to a brace instead of a stock, buy the tools to do it all, you are just better off spending a bit more and having another gun.

Catshooter said:

Thanks for the reply WK.

I do have the tools and at least some of the skills to use 'em, the barrel is sitting naked on my bench now.

I did give some thought to the gas system. I have a factory built pistol with a 10.5 barrel. It is set up with a carbine length gas system that looks just like the one on my donor rifle. The only thing I haven't checked is the barrel port diameter between the two. Do they change that port size?


Cat

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I don’t know about port size, but it seems reasonable that they might. Before you go cutting, recrowning, barrel threading, and possibly adjusting ports, I would seriously look at the cost of a barrel versus the time taken to make it happen. Of course there’s the pleasure of doing it yourself, but monetarily that’s not always the best route.

Don'tcut the barrel unless you are trying to make something weird.
You can buy a barrel in most calibers and in any just length you can think of.

Oh ok almost no one has the gear to do that.

Reading your post, you're not really replacing a lower so much as assembling a new AR (pistol) with done parts you already have.

Buy a fresh lower, and start pinning on parts!

I'm with the guys above, don't cut that barrel to save money. OTOH, if you're just machining for the fun of it, rock on.

edwardware said:

I'm with the guys above, don't cut that barrel to save money. OTOH, if you're just machining for the fun of it, rock on.

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If the barrel has no other use to him and he has the ability to cut, crown, thread and enlarge the gas port himself, no good reason to spend money on a new barrel and have that one just hanging out, a useless investment. The market also sucks for AR parts availability right now, barrels included. I just bored & taper pin reamed a new barrel and FSB for a guy who spent quite a bit more to buy separate parts and have this done than a barrel with an F marked FSB already on would have cost, but he couldn't get one, out of stock everywhere.

I agree with the above that this sounds more like you’re building a new weapon with parts from something you already have. As long as you keep track of which Lower is which, I don’t think you would have any issues.

As a representative of the hobby machinists in the crowd, it would be awesome if you could do a write up / photos of the process. I know what needs to be done, I just enjoy seeing that kinda stuff. And who knows, I may pick up a new technique / trick or two. At least let us know what you find regarding the port size.

Catshooter said:

Well since I can cut, crown, thread and do ports all for zero cost dollar wise it's the way to go. I would like to know if I need to adjust the port though. Maybe I'll take apart my AR pistol and measure it's port diameter. I know it's placed the same distance as this one is, their gas system are (externally) identical.

I'm not concerned about the mechanical aspect of the job. Unless there's something I don't know, which of course is a giant possibility. I think I've got the legal issues covered but I wanted to ask around. There's certainly people here that know way more than I do.


Cat

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Most barrels are over gassed so try it and see if the bolt will lock open on the last shot.
Load one round in the mag and fire, if the bolt locks open you should be fine. If the bolt doesn't lock you may need to open the port.

If you have to open the gas port go 1 drill size at a time until the bolt locks.

FYI if adding a suppressor I've cut 16 inch carbine barrels off 1 inch in front of the gas block (9 1/2 inches) and they work perfect (suppressed) without opening the gas port.

SC45-70

Catshooter said:

I have a 16" AR pattern carbine. I want to replace the lower with a new never been anything one (that it's first assembly will be as a pistol), replace the butt stock with a brace and cut the 16" barrel to 10.5.

Anyone see any legal issues with this? And that is the sequence of actions I'll take, in that order.

Thanks.


Cat

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Build a separate pistol. No legal issues and much easier.

Catshooter said:

Well since I can cut, crown, thread and do ports all for zero cost dollar wise it's the way to go.

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Why are you asking us, then?

You're fine on the legal end of it.

Catshooter said:

I have a 16" AR pattern carbine. I want to replace the lower with a new never been anything one (that it's first assembly will be as a pistol), replace the butt stock with a brace and cut the 16" barrel to 10.5

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Before cutting, check the gas port size. As the plan is to trim the barrel to 10.5", I assume it has a carbine length gas system and the gas port should be .0625". If it's not a Colt barrel, it could be larger. If it's .0625", that's about where it should be for suppressed use with a 11.5" barrel, maybe a little on the large side depending on the can.

I've done some shooting 5.56 with 10.5" barrels and 11.5" barrels, suppressed and unsuppressed. I much prefer the 11.5". The 11.5" gives more velocity and has the edge in performance out to 300 yards or more, is a little more reliable and a bit more forgiving. A lot of shooters prefer the 12.5", claiming it's in the sweet spot between 10.5" and 14.5". I've not had the chance to put one through the wringer.

Thread the muzzle for 5/8-24, if the barrel is thick enough. It leaves more material at the muzzle to eliminate possible coning of the bore and is better for mounting suppressors.

My best shorty setup is an 11.5" barrel, BRT Micro Port, A5 RE with an A5H2 buffer, Sprinco green spring and Omega direct thread suppressor. I have a BRT 11.5" OPTIMUM SBT Suppressor Barrel 5/8-24 Tapered Shoulder that I suspect I'll like even better once I get the upper built.

I though a 10.5 " & 16" have the port in same place, dont they? I believe a navy (10.3,actually) has the port reamed out a bit.

Ah, yes. The 'ol DIssapator. I believe they are rifle length.