hk legend, and my shego!!!(shocker with an ego frame)
pretty much every upgrade.
The way they made it the barrel gets loose pretty easy.
this barrel is amazing!! i would hasate to buy it if you have the money. i got mine for free =D its VERY accurate!!!! QUITE!!!!!!!! it really inproved my efficency. my old barrel was at 300 fps and once i put it on it went up to 320 fps!!!! if you want a top barrel.... get this!!!!!
the best thing is that if you want to put it on a different threaded gun you just have to get a different insert!!!! =)