who makes the kit for gas piston conversions. i remember one the fit under normal hangaurds. is there one that is available in rifle legnths? and info really on the gas-piston AR's and kits and options.  thanks in advance.

Leitner-Wise does conversions on customer provided uppers and sells piston uppers. Currently only carbine length are available.

POF I believe offers a rifle length system, but don't quote me on that. Maybe Frank from POF can chime in. POF only offers new uppers

ARES said they where going to be offering a carbine length piston system about 6 weeks ago. Since then they have pretty much disappeared.

The Rhino system was a piston system from the 80's and is no longer produced