AR question

Went to the range today with a buddy with his new ar pistol that he built. When we were shooting brass cased federal ammo it functions flawless. Then the Tula Russian ammo would not strip a fresh round but it would cycle the bolt. Is this just a problem of underpowered ammo? Or something else?
Thanks. It’s a 10.5 inch barrel for what it’s worth.

 

Just under powered ammo.

The short guns are particularly sensitive to it in my experience.

After breaking it in real well with full power ammo, and running it wet it may function better in the future.

Edited to add:
I had a 10.5" that choked fairly often on the cheap steel cased ammo when new, but after a couple hundred rounds it ran them real well even when the BCG was getting a little dry. I don't think it had any hiccups after the first 250rds.

 

Makes sense and thanks for the reply. I don’t know enough about ar’s but I was surprised that it was cocking the hammer without stripping a new round.

 

It means the bolt isn't going back quite far enough. Close, but just not quite there.

Once it's broken in and running smoother it may function just fine.

If it's still having issues, a lighter buffer weight may alleviate the problem. I'd personally hold off for now on that. If he swaps it now, once it's broken in it may beat itself up, especially with full power ammo and cause parts to wear prematurely/break.

 

I always cycle the bcg around 100 times by hand on a new rifle/build before ever firing it. This helps break everything in and avoid such problems.

 

As the other's said, most likely underpowered Tula.

Did you try one round in the magazine and get the bolt to lock back? That's the usual test when adjusting an AGB, it's also an indicator for weak ammo or not enough gas. The gas you've ruled out due to the reliability with the Federal. Also when I'm 'breaking in'' an AR15 I go sort of heavy on the lube.

 

You have at least 2 things at work here- 1, a pistol AR- they often have cycling issues due to the gas system and buffer issues. This can make them sensitive to certain ammunition types. Second, the steel cased import ammo will often choke in AR's of all descriptions that are otherwise reliable.

 

I do this with all my AR's new or built at home.

So very true. Yes AR's with pistol length and carbine length gas systems (with short barrels) can be finicky. I too have seen AR's that run great with good quality brass cased ammo choke on the cheap steel cased ammo.

Another thing to do with a new AR, bought or built, is to run at least 100 -200 rounds of true MIL SPEC M193 or M855 5.56 ammo through it before trying anything else.

 

No we didn’t try that. Wouldn’t been a good idea. Gonna try and make another range trip soon with better ammo. One thing that wasn’t a problem was annoying others at the range. Ar’s are loud as it is, ar pistols are crazy loud. Good times.

 

A "linear compensator" is particularly well suited to AR pistols.

It dosen't make them any quieter, but it throws most of that blast forward instead of back/to the sides and certainly makes them more pleasant.

Something like the KVP linear comp.

 

Agree 110%

I've got a BRT Covert Comp on mine, makes a world of difference on a 9.5" barrel. Whatever you do avoid a brake, unless you're really, really, into annoying the other shooters on the firing line. .

 

Im going to agree with the others on lower powered ammo. 10.3 and 10.5 inch ARs are already on the edge of reliability with full powered ammo. The gas port is so close to the muzzle that the gun does not have a lot of time of full gas pressure to run the system. That's actually why you see the 11.5 inch barrel historically. That extra inch of barrel increases the time that the system has full pressure by something like 50 percent over a 10.3. The newest generation of the military Mk18, the URGI, is moving to a 11.5 inch barrel.

Now that doesnt mean a 10.3/10.5 inch gun cant be reliable. It's just they are more susceptible to problems when running weaker ammo.

A couple years ago I chrono'd several ARs and several ammo types. American Eagle 55 grain 223, M193, and Tula 55 grain. Out of my 20 inch FN barreled AR the M193 ran somewhere around 3200 FPS and the American Eagle 223 was fairly close but a little lower. I want to say in the low to mid 3100s. The Tula was down around 2950 FPS.

 

We, the gun community, have learned a lot about ARs in the last 15 or 20 years. Of those things is what it takes to get an AR to run reliably. That means the 10.5 inch as well. Once I understood the triangle between gas drive, reciprocating mass and spring, getting a 10.5 inch to work was child’s play.

For a 5.56, just use good ammo and a buffer weighing roughly between 4.5 & 5.5 oz with the appropriate spring (standard carbine or rifle) all that’s left is porting it for unsuppressed or suppressed.

Yes, the shorter the barrel, the greater affect small changes have, but a 10.5 can be setup with little trouble.