Im looking for anyone who is or has been an armorer. I have a question or two.

I assume this is the question about the ZM4?

Flashbang_E4T.....interesting weapon for just plinking.

As you probably know, the ZM4 has some novel features that make this a versatile weapon. The 1st thing I would check is the barrel locking mechanism. Do you have another barrel to swap out? Is the barrel locking mechanism on each barrel or integral with the receiver?

One other thing is the extractor itself. The extractor on this weapon is beefed up, and shouldn't be causing problems, so the issue could be with the shell casings themselves. You indicated that you used some cheap ammo in it, and by all appearances the weapon functioned well until you swapped to match-grade ammo. One possibility is that the cheap ammo casings left a build-up on the extractor itself? Was the cheap ammo casing made of a different material than the match grade? Do you have access to any mil-spec 5.56? Have you checked the extractor spring itself? Is the extractor spring seated correctly when re-assembled? Does the extractor pin show any unusual wear pattern after being cleaned? Is it a tight fit?

Only other comment I have on your issue, as the cheap ammo worked flawlessly, I'd recommend switching back to it for both economy and functionality sake.

You assume correctly Gunny. That you for the assistance.