Problem : Using a fully-loaded preban Adventureline mag upgraded with MP GenII follower (spring was NOT upgraded), I encountered a couple of failure to feed. The BC locked back/bolt catch was engaged. Previous shell extracted but the next round (to load) just move a bit forward in the mag and DID NOT load into the chamber. It's either I had to release the bolt release or rack the charging handle to load the (next) round. Happened twice. Ammo is LC in stripper clips.
Set-up : Bushmaster M4 barrel on flattop upper; regular buffer sping with H-buffer.
What could be the cause?
Is it the recently upgraded H-buffer?
or probably a weak Mag spring?
I'm not sure I get what you're saying.
You mean with the bolt catch engaged, you release it, and it doesn't strip a round out off the mag? Only slides it forward a little bit? How far?
You racked the charging handle, or the forward assist? That's what the FA is there for, but you still shouldn't have to use it.
The follower should have nothing to do with it. Try a different mag or replace the spring. The spring could be applying too much upward pressure causing the round to drag along the outer edge of the mag causing a lot of resistance.
If it still does it with another mag, I'd look into a different buffer/spring.
ETA - Also try taking a couple rounds out. For example, if it's a 30 round mag, try 28, or even 25. Make sure all the rounds are seated probably in the mag by hitting it a few times on a table or such. If they are getting hung up on the front of the mag, it's probably a weak spring.
Original post edited to clarify malfunction.
A few things to check, that I've seen bad with my gun and first round fail to feeds...
Check that the hammer isn't sticking up too much from the lower receiver (from what I gather here, it isn't supposed to be over 11.4mm). Check for burred up ramp on the underside of the bolt carrier.
Check the firing pin collar and see whether you're using a M16 firing pin or an AR15 firing pin. On my 2 guns, the hammer is chewing up the rear of the firing pin collar.
Just some ideas.