Buddy of mine just picked up a CMMG Banshee 9mm. Sweet looking gun.

We threw a Trijicon MRO on a Geissele 1/3 mount on top.

Took it to the range today and every other round was not ejecting from the gun.

The spent cases were dropping into the breach and jamming up the gun.

We tried a bunch of different ammo. 115 grain winchester, remington, magtech, blazer brass...

All of them had the same issue.

Tried some of my 147 grain subsonic Blazer aluminum cased ammo. Same thing.

We even tried swapping out the trigger/hammer with a Geissele SD3G. Same issue.

Swapped out the buffer and spring with the setup from my 9mm gun. Same issue.

Any ideas on this? I haven't done much googling. I did find one other case that sounds like this. No answers on that one.

Sorry for the problems your buddy is having. Please have him contact our Tech Support at [email protected]. They are out for the day already, but should be able to respond when they are back in the office tomorrow.

Both of us contacted the tech department.

We were told to use "hotter ammo."

It is not an ammo issue. The spent case is being dropped inside the receiver. It is not ejecting from the gun.

The spent cases  are extracted from the chamber and then dropped into the magwell/breach/receiver area.

Have you seen this thread?:https://www.ar15.com/forums/ar-15/Thoughts-on-the-CMMG-Guard-/15-713060/&page=20

It would be great if you could chime in over there as the more data the better.

Several of us are having issues with the ejector spring failing at around 1K rounds.

I have done a lot of testing and documentation here: http://c3junkie.com/?page_id=954

The factory CMMG RDB ejector spring is shorter than a standard 556 spring but the coils are thicker making it stiffer/stronger.


Maybe someone assembled the bolt by accidentally using a standard 556 ejector spring.

In my experience, once you start seeing under 5lbs of force to compress the ejector spring flush with the bolt face, you will start having FTE's.


How many rounds have you fired?
From your post it sounds like it is new?  Or new to you?  Previously owned?

If brand new, maybe the BCG is binding in the upper?   If you remove the upper from the lower, does the BCG move freely in the upper?

Longer 9mm buffers shouldn't be used in the CMMG RDB due to the bolt / carrier relationship.

What kind of buffer and spring were you initially trying to use?

It belongs to my buddy. He just picked it up last Friday. We went and shot it Saturday morning. Was doing it right out of the box.

Sent pictures of the ejector to CMMG. They say the ejector looks a little set back in the bolt. They're sending him a new one this week.



It's the original CMMG buffer and spring that came with the gun.

I resorted to a softer, shortened, takedown detent spring to adjust the ejection timing.
Agreed that the fixed ejector is the way to go and have been contemplating methods.
I need to modify or replace my 1st generation EndoMags to allow hollow points to feed..