Ar Problem(s)

[George]

If it locks back on an empty mag every time with premium 69 & 55 grain ammo and still doesn't with the Remmy stuff, I would put some of the Rem over a Chrono. If it ain't making 3000fps + you have your culprit and there is NOTHING wrong with this rifle that decent ammo won't cure.

55gr has to make 2950+ to be worth putting downrange and really ougta' be 3000+ in a 20" bbl. I ran across a batch of PMC 55gr a couple years back that was shooting like mousefarts and barely cycling my AR's. I chronoed it and got 2750fps and found that it was not locking any of my AR's back on last shot and was not picking up rounds in my JP CTR-02 with the gas block turned down.

The entire batch was running under 2800fps!

[ken hebert]

Chuck, if you want to try running some ammo through a chrono, I've got two we can use. Truthfully, I need to do this myself. My recent AR build is giving me some of the same problems you are having, so I'm following this thread closely. I'll be at OGC for my match on Sunday, and am planning to try the AR+chrono thingy after. I'll also try and remember to throw those CZ basepads you wanted to try in my range bag.

Ken

[StealthyBlagga]

If it locks back on an empty mag every time with premium 69 & 55 grain ammo and still doesn't with the Remmy stuff, I would put some of the Rem over a Chrono. If it ain't making 3000fps + you have your culprit and there is NOTHING wrong with this rifle that decent ammo won't cure.

He said:

The rifle functioned 100% with the American Eagle ammo, but locking the bolt back on an empty mag was a sometime thing.

I think the advice about using good ammo is right on. Hopefully the gun just needs to be broken in a bit. However, if it is not locking open every time with good ammo like American Eagle, then you still have an issue. Sometimes a leaky gas system can fix itself by depositing carbon and blocking the leak. Why not run 500 rounds of American Eagle through the thing and come back here if it is still not locking open on an empty mag reliably ?

[revchuck]

SUCCESS!

While you guys were typing away here, I took the rifle back to the dealer I bought it from and explained the problem. At first he didn't want to believe me, but we've been knowing each other for over ten years now, and he knows that I wouldn't BS him. He had taked the gun out when he took it in on trade and shot it, and it ran for him with that ammo. When he thought about it, and the fact that it ran with the hot Federal match ammo, he wondered if he had checked it with some hot Philippine milsurp which would've run anything. Anyway, he replaced the gas tube and the bolt and bolt carrier. (Yes, he checked the headspace.) We took it out to the woods - living in a relatively rural area has its advantages - and put some of the Remington ammo that had given all the problems through it. It perked right along, throwing the brass out farther than before and locking back positively on the empty mag.

Thanks to all of you for your help and patience on this. This is a big part of why I'm glad to be a shooter.

[George]

Hot ammo is the bandaid fix for gas issues. An AR should always run with any 55gr that goes 2900+ if the gas system is OK. If it aint, the hotter stuff will mask it. My guess is worn rings, or poor gas tube to carrier key fit were the actual culprit.

[ap3]

Hot ammo is the bandaid fix for gas issues. An AR should always run with any 55gr that goes 2900+ if the gas system is OK. If it aint, the hotter stuff will mask it. My guess is worn rings, or poor gas tube to carrier key fit were the actual culprit.

Brownells sells a replacement kit for $30.00

231-000-045 Rifle Gas System Kit

inluded are rings,gas tube, carrier key.

[gotm4]

Sounds like short stroking. This is usually a loose carrier key. The way to test it is to put 1 round in the mag and shoot it. It should lock back EVERY TIME if it doesn't you're leaking gas at the key (most likely) or at the gas block (least likely).