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

Not that I'm an Armorer....but have had plenty of experience with weapons...
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. Thank you for your assistance.

Let me know if it actually helped, or I was just blowin smoke up yer tailpipe with the advice....

Roger that Gunny, Ill keep you informed. I got finally had time to get the full cleaning of the weapon done today and I oticed there has been some physical damage to the weapon itself. The blueing has been worn away from the interior top side of the upper reciever where teh charging handle slides back and forth. Though this is normal it all occurred very quickly. The charging handle itself has some damage on the forward bottom tip just under the gass tube hole. The forward end of the ejection port has also been slighlt deformed from the malfunctions causing brass to slam into it. Im more than slightly worried that my fairly hefty investment in a firearm is being ruined here, and from all I can see for no apparent reason. I found nothign wrong with the bolt housing group or the entire upper reciever aside from the damaged caused by the malfunction. Fortunately I have a warranty with DSA but Im hesitant to return the weapon due to lack of knowledge of the cause of the malfunction.

Return the weapon to DSA asap. Damage to the gas tube will only worsen with continued use. Best to get the entire tube assy replaced, especially if all it costs you is a little time and cost of shipping!

Take detailed pictures, digital hi-resolution if possible, to document all the existing damage, print a copy off, circle the areas of your concern, and include them in with the weapon. This accomplishes two things, one it keys in the manufacturer in on the immediate problem, and secondly, gives you something to compare to when the weapon is returned to you.