Those who had been around probably remember the tiny ad of Z-M weapons in the old gun rags. There appears to be controversy on the system over the internet from time to time - so finally we got to talk to Allan Zitta, the designer of the system.
From the man himself, Allan described the ZM as a "direct impingement" system. It works exactly like an AR - other than the extended gas key and shortened gas tube. When we asked Allan the objectives of his original design, he explained that he wanted to make a short barreled AR that works, and the issue of early extraction with a shortened gas tube.
To solve this problem, instead of lengthening the gas tube by winding it around the barrel like the pig-tail system, which starts sagging under heat, he made a manifold in the gas block which increases the dwell time of the gas flow.
Wait - why don't people actually put this in plain English in promotion literature? All these gun rag blah blah blah on delayed impingement gas system mumble jumble is really talking about increasing the gas dwell time before the initiation of unlocking. LMT did it inside the bolt carrier, Allan Zitta did it inside the gas block......20 years ago.
We also took the opportunity to ask Allan point blank about the spring problem. Allan smilingly replied that he did not know that he needed a special spring for the gas system so he just put in a generic spring - but he learned the lesson right after the first batch of the original ZM weapon was made. The current version is using the proper spring for the application.
i think we all should give the man more credit.