Had a weird issue w/ BCM upper


Full Access Member
I have a complete BCM upper (w/ BCG etc).
Issue is that sometimes the BCG gets stuck on the return from the buffer tube.
Almost at the bolt hold open position but not quite... but a bit further.
it doesnt do this 100% of the time but maybe 20% of the time as a magazine empties.

In the beginning it only did it so rarely I thought it was afluke and was easily cleared.
But now it does it much more often and can be cleared only with difficulty

...sometimes all the way up to mortaring to knock it back forward.
It will go back when I try to clear it but will get stuck again at same place maybe not quite an inch past the bolt-hold open postion.

I thought at first maybe this is an issue with the lower. So I switched lowers (from Bushy to Sig516 lower) took it to the range another day..
Still does it, rifle completely locked up within a magazine.
Then I thought..

Well the only moving part really is(are)the BCG and components so I switched out the entire BCG .

Now I am at home and I cant test it on shooting but even with this other BCG it still does it when I check it via hand cycling.

Same symptoms as on range but I did notice it seems to happen more when the rifle is held canted towards the left..

Round count is lowish... upper may be a couple years old but I only now broke it out of my stash and decided to exercise it.

Round count is still fairly moderate maybe under 2000 rds I think and the issue seems to increase in frequency as of late.

its bad enough not cannot even be used in training (never mind as a go-to)....

It had been suggested to me a problem with the FA might be at fault.

Was going to disassemble the FA but my punches seemed to be either too large or too small, figures.

However when fingering the FA from the inside I noticed the front tip of the plunger seemed real loose going in and out w/o any relationship to the FA button.
Real odd and then I was actually able to pull it out!!
How could the plunger tip become loose like this?

I bought this rifle used with very low round count (as verified by inspection) and understood it to be factory.

And the bolt and BCG were both BCM (BCG marked of course and the bolt had the correct appearance) which seemed to back up the claim.

However can one ever be sure?

So then I just attached lower and upper back together and called it a day.

I never use the FA anyway.
Glad to have my rifle back (even if it was just a back-up)


Super Moderator
Can't help you with this problem. But let us know what you find out in case anyone else experiences this.


Full Access Member
Sorry if my post wasnt more clear.
Not my best piece of writing.:emotions33:

Actually I solved the problem by simply removing the loose tip of the Fowrad assist plunger once I realized it was loose.

Have not reinstalled it since I neve ruse the forward assist anyway :)

Actually I am really stoked my rifle is back in the fight as I feel nervous when I am down to only a single working fighting rifle at my place.
Now back to 2...

And best of all they both handle my hard primer stash of ammo like champs due to the RedX extended firing pin.
Even after I took out the Wolff Extra power hammer springs .. yayy!

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