New upper on a older lower.

[RED]

I put a new complete 5.56 upper on a Cmmg lower I’ve Had for years. It was a tight fit but not overly tight. The action fed dummy ammo Ok. I took it to the range and everything worked. Single rounds, 3 rounds rapid fire, and no problems. Then I tried to hand eject a chambered round. It took a younger stronger hand to do it. A fired round has enough energy to extract but my 76 year old arthritic hands aren’t strong enough.

What gives here?

[lyman]

BCG lubed well?

barrel and chamber cleaned before you shot it?


ammo used?


did you have trouble pulling it back when you loaded it?

[PWC]

Sounds like a reverse "bolt assist" is needed

[lyman]

does it exhibit the same problem (bolt tight, hard to pull back) when seated in place with the upper off the lower (and no round in the chamber of course)

[RED]

No and no. I cleaned the chamber, and stripped the bolt and lubed it with some LSA. I ran some inert carriages through the action and everything worked fine. I chambered a live round and it extracted normally. It only gets hard to extract if the round is seated after firing a live round.

I think if I put 50 rounds of LC Milsurp ammo, it’ll clear up

[lyman]

No and no. I cleaned the chamber, and stripped the bolt and lubed it with some LSA. I ran some inert carriages through the action and everything worked fine. I chambered a live round and it extracted normally. It only gets hard to extract if the round is seated after firing a live round.

I think if I put 50 rounds of LC Milsurp ammo, it’ll clear up

let us know how it goes

[Former Cav]

Look at the chamber carefully. My Bear Creek Arsenal 6.5 Grendel upper chamber has a "groove" in it. Every now and then I have to pogo stick it. I've bought a new barrel.