While I am waiting for the gubmint to approve my ThunderBeast 30P-1, naturally I am looking at things to spend money on so my other guns can accept it. I have an older Olympic Arms AR-M4 with the short barrel and a welded on extension that makes it legal and makes it look like a 20 gauge. I'm not sure what this configuration is called. This gun is an old pre-ban shooter with a slide fire stock and is just for killing zombies. :gun11: I am thinking about changing the barrel to something like this so that I can put my suppressor on it. DPMS AP4 Barrel AR-15 5.56x45mm NATO M4 Contour 1 9 Twist 16 Chrome I am also interested in the gas piston conversion kits. Opinions on the conversion on the zombie killer vs buying a gun with it already on it? Some kits use the existing front sight post Osprey Defense OPS-416 Gas Piston Retrofit Conversion Kit AR-15 And some replace it CMMG Gas Piston Retrofit Conversion Kit Gas Block 1-Piece Bolt Carrier Thoughts?