I'm installing a collapsible stock on my lower and the buffer retention pin keeps popping out when I run the charging handle.

The retention pin and spring pops out and usually lands in the trigger group.


The lower is stock Colt.  I've just put it together with a new DPMS upper that has a chromed bolt carrier.

Do I need a shorter buffer spring when I go to the collapsible stock?  I can't think of anything else that could cause this problem.

Thanks for help!

I just measured the buffer spring and it is 10 1/4, within the specs for the collapsible stock.

Any ideas?

You need to screw the buffer tube in one more turn.

Hey thanks, that took care of it.

How come no one said the lip of the retention pin needs to be "tucked" under the buffer tube?

Learn something everyday.

Oh, the buffer pin is tucked under the buffer tube. [LOLabove]