The AR 15 is the only direct impingement gas system on the market. It was designed in the 1950's. There are no new gas impingement rifles on the market, just lightly modified AR 15's. The Bren, G36, Carmel, ARX, L85, etc. all use a very slight variation of the AR 18 gas system/carrier design. Strangely, there are more rifles using the long stroke piston system of the AK then there are direct impingement systems. It's odd because DI is lighter has fewer components and is at least as reliable as any of them and you would suspect it would be cheaper and easier to build.