The folks at CMMG have come out with an AR-15 gas piston conversion kit.  It comes with a new gas block, piston and bolt carrier (so it works more like the AK).  As far as I know, before this conversion kit you had to buy a whole new upper for your AR if you wanted a piston-driven system.  It’s an attractive idea in some ways, especially for those who’ve had problems with carbon fouling in the bolt carrier.  The piston system keeps more of the carbon out of the receiver and it’s great for use with a sound suppressor, in which case it keeps more of the trapped gasses from blowing back into your face.  The conversion kit’s price is roughly equal to that of a new AK rifle and several spare magazines.

However, they call their piston kit a “direct impingement gas piston system.”  Anyone else see a problem here?  It may be nitpicking (and please correct me if I’m wrong) but “direct impingement” is exactly that one thing that a piston system is not.  When Stoner came up with his piston-less operation back in the day, he called it “direct impingement” to describe his system of channeling the gas back into the receiver where it “directly impinges” on the bolt carrier without an intervening piston rod or tappet.