Thordsen buffer tube cover on mine. Uses the stock carbine buffer tube which is good since I couldn't find a decent pistol tube anywhere in stock and I had a bunch of carbine tubes in the parts bin. It secures onto your carbine buffer tube with screws and gives you good length and overall girth to make it easier to shoulder if you had to. It also has attachment points to put a cheekpiece on if you need extra contact points. Best part of all, it only costs $27.
Cool story, bro... when do you get to the part where you shut up and walk away from me?