Difference between DI, piston, and DIGS AR15s?

[WyoGunner]

Okay, so I understand the difference between the direct impingement and piston system, but how exactly does the Para Ordinance Delayed Impingement Gas system work? It seems like a hybrid between the two. Thanks.

http://www.paraord.com/new/video_ttr.php

 

[SIGWatchman]

Interesting. It appears to be a modification to the DI system. An extended gas key of sorts along with a different setup for the gas tube. Buffering and return to battery operations are now handled in front of the bolt and carrier instead of in the stock allowing a folding stock option.

Looks to be a good improvement if it all works as planned.

 

[Sig685]

Para uses the ZM action. It's not new, it was designed some years back by a smart guy called Allan Zitta, if memory serves. Whereas most gas piston ARs simply replace the gas tube with some form of piston and have that act on what is essentially a standard bolt carrier that travels back into the buttstock, the ZM system uses its own bolt carrier which is much shorter than a regular bolt carrier. Also the gas block on the Zm system is much longer than a regular gas block and the recoil spring is in front of the action rather than inline with the barrel, bolt and bolt carrier.

So in effect, the ZM system uses a short bolt carrier and moves all the action in front of the rifle, alongisde the barrel. The gas still comes out through the bolt carrier but is supposedly vented out more than in the regular DI which sends it gas out the ejection port and some stays in the action also.

I have never used the ZM system, but to my mind, it is no longer an AR-15, it's just a semi-auto rifle that happens to use AR-15 magazines. That is attractive to some people, not me.