BCG Failure Analysis, need a little help

[Tim K]

5.56 BCG from IMI, I think. It has roughly 500 rounds on it, likely less.

The first problem with it was that the cotter pin that retains the firing pin would be bent every time I cleaned it. I never figured that out, but decided I didn't care.

Today, one of the screws holding the gas key sheared off under the head. The key is still tight, and there is no sign of the gas tube taking a beating. The head bounced around in the trigger area causing a few problems but no damage.

Do those two events seem related to anyone (aside from being a sign to not buy IMI BCG's any more)?

I think I'll spring for a better BCG and put this one in the box as a spare after fixing it. What should I buy?

[asmo]

Picts please. Having a hard time visualizing.

I am running BCM in everything without issue.

[BPTactical]

Shitcan the gas key and screws. Once they break loose they will never hold tight again.
My guess on the FP retainer is you may have a slightly out of spec firing pin.
How is the recoil on it? If it seems harsh the rifle could be overgassed or the wrong buffer/spring.
Hard to diagnose on da webz.

[Tim K]

Hard to say on the recoil, Bert, I only shoot it suppressed. If anything, it seems a touch under gassed. On occasion, it won't lock back on the last round.

So, new gas key, screws, and firing pin. Got it.

[Great-Kazoo]

Hard to say on the recoil, Bert, I only shoot it suppressed. If anything, it seems a touch under gassed. On occasion, it won't lock back on the last round.

So, new gas key, screws, and firing pin. Got it.

Possibly too much back pressure with the suppressor. Replace cotter pin and gas key. Run 100 rds and see what the cotter pin looks like.

[MarkCO]

Bent cotter pins are typically from lightened carriers or FPs or over-gassed systems. A light carrier with a XP (Tubbs or JP spring) will also bend them and may be on the verge or regular slam fires. If you are piercing primers, that will also bend the cotter pin. You can heat treat the pin or get one of the KNS solid pins. If you know which side is getting impacted to casue the bend, that will help to figure out the cause.

[ray1970]

What should I buy?



I am running BCM in everything without issue.

I'll toss a second vote for BCM. I run them almost exclusively. Never had an issue.

[beast556]

I would get a new BCG, another +1 for BCM.

[Tim K]

Bent cotter pins are typically from lightened carriers or FPs or over-gassed systems. A light carrier with a XP (Tubbs or JP spring) will also bend them and may be on the verge or regular slam fires. If you are piercing primers, that will also bend the cotter pin. You can heat treat the pin or get one of the KNS solid pins. If you know which side is getting impacted to casue the bend, that will help to figure out the cause.

I think you mean is it being bent forwards or back, correct?

I think it's being bent back. That would indicate over gassed, right?

[BPTactical]

I think you mean is it being bent forwards or back, correct?

I think it's being bent back. That would indicate over gassed, right?

That would be correct. If you think about it, it can't be bent forward unless the firing pin is going too far forward to the tune of 3/16" or so. Sorry Tim, I missed the part on shooting suppressed earlier.

[Tim K]

If it's over gassed, can I address it with a change in spring, buffer, or BCG, or do I need to go with an adjustable gas block?

Could over gassing it also have caused the sheared gas key bolt?

[MarkCO]

More mass should reduce the battering. If that does not help enough, adjustable gas.

[Tim K]

Adjustable gas block is on order.

[cofi]

Adjustable gas block is on order.
Who did you go with?

[Tim K]

Who did you go with?

http://www.jprifles.com/buy.php?item=JPGS-5B