Colt commando upper starting to get froggy

[The Dumb Gun Collector]

Well! It's back. Now it is clearly over gassed. I can feel the bolt being more violent. And now if I run my surefire socom it will lock back with rounds still in the mag. The issue goes away if I remove my suppressor. I just ordered an EZ tune with the dedicated suppressor option for carbine gas.

[georgeib]

Does it feel like the bolt catch spring is weak? Also, does it do this with different mags?

[sinister]

The second malfunction was an empty case stuck above the bolt, oddly, with an unfired cartridge in the chamber (the empty case was sticking out of the ejection port.

I have had this upper for a long time (about 7 years), I have shot if with thousands of round of steel, 22, brass, etc. It has gone through many phases...

... 55 grain Hornaday Frontier. That ammo has run perfectly in every gun. I was shooting it with my Surefire Socom as usual. I will say recently I have been shooting it with Tula steel without the suppressor and it was running fine. I wonder if it is finally over gassed?

So, AR masters....What say you? Give me your best diagnostic tips and I will do what I need to do.

You need a new barrel. About thirty minutes work if you're doing it yourself.

You're addressing symptoms, not root cause.

[B52U]

Those EZ tunes work great at taming the old carbines with oversized ports. The guys at BRT know what they're doing.

[The Dumb Gun Collector]

You need a new barrel. About thirty minutes work if you're doing it yourself.

You're addressing symptoms, not root cause.

I know you are right! I’m being a doofus

[danieljmaunder]

I cleaned it up paying particular attention to the extractor and chamber.. Replaced the buffer spring (which was visibly shorter) and fired 100 rounds of federal 55. Functioned fine but noticed it was ejecting around 1 o'clock. Might be time for a h3-4 buffer?

For your future reference, minimum length for a carbine buffer spring is 10-1/16 inches. Its an easy check when your round count is getting up there as it can be measured with a tape measure. I check them about every 6 months or so with the amount of shooting I do on personal guns. At work they get checked quarterly. As others have stated, probably time for a new barrel as it seems like you have some port errosion leading to overgassing.

[Clint]

Agreed.

Random lock backs point to an issue with the bolt catch assembly.

Does it feel like the bolt catch spring is weak? Also, does it do this with different mags?

[The Dumb Gun Collector]

Does it feel like the bolt catch spring is weak? Also, does it do this with different mags?

It does it with mag and d&h. It only happens when suppressed at this point. If I remove my suppressor and shoot std pressure or steel the issue goes away. I will compare the bolt catch assembly tomorrow so I dont wake up the boss lady.

[georgeib]

It does it with mag and d&h. It only happens when suppressed at this point. If I remove my suppressor and shoot std pressure or steel the issue goes away. I will compare the bolt catch assembly tomorrow so I dont wake up the boss lady.

I can envision why a weak bolt catch spring, or possibly other worn components too, would prematurely cause the bolt to lock back when suppressed. I'm fairly sure the root of the issue is likely due to the increased bolt speed, which would be mitigated with one of Clint's gas tubes, but I still think it's quite possible that a weak spring may be contributing.

I'd be tempted to test it, in lieu of replacing the spring, by stretching the spring, and then trying it for a mag or two. Not sure if stretching the spring is a big no-no, even if you plan on replacing it in short order.

[Clint]

The whole bolt catch assembly needs to be looked at, not just the spring.

It's possible for the spring bore to become peened, which prevents movement of the detent and allows the catch to float without effective spring pressure.

Upon close inspection, it should be obvious whether the catch has enough spring tension.