So I've got a nice 10.5" barrel and a good upper receiver laying around and decided to do an SBR build. Form 1 is sent off and I'm just waiting for it to come back to do some shopping. I've got enough parts here that I don't want to buy a complete upper, but, this rifle will probably carry a supressor most of the time. I start looking into adjustable gas blocks and a gas buster charging handle and bolts and forends, and start to notice that the money I spend on all of this would buy an aftermarket piston system. I'm not a big fan of piston ARs, but I've shot enough short guns with suppressors to know that I hate the gas blowback. Piston ARs aren't much better, but they do give noticeably less blowback. What do you guys think about the drop in kits? Any of them worth a damn?