I've got a Glock 21 and I would really like to suppress it. I know suppressors are legal in AZ, so I've got that covered. This is where I fall into the unknown. Correct me if these assumptions are incorrect. 1. I need to get an ATF tax stamp ($200 or so) and some various other paperwork. What paperwork do I need? 2. The suppressor. I want to get a Gemtech Blackside. 3. Extended threaded barrel. Will be had from LoneWolfDist. Says they're threaded especially for Gemtech suppressors. 4. Ammunition. I hear subsonic is the way to go, for obvious reasons. Do you have to use ball ammo or can hollow point be used? There's another question I'm not 100% on. Do hollow points expand upon leaving the barrel or do they expand when they hit their target? Anyway, all help would be appreciated. Thanks much.