OK. I have over 60 firearms but have never been interestead in owning a "BLACK RIFLE". With the upcomming election I am worrying about restrictions on the horrizon. It could be nothing but I have started to accumulate lowers. I have 8 so far and am trying to put together 25 AR-15 lowers by the first of the year. I am going to try to fit at least 1 AR-10 in there and about 7 to 10 AR-10 lowers in there somewhere. So now that I have rambled on here is the question. What are all the calibers that I can build uppers for the AR-15 lowers? If there are more than 25 then I would like to know. I want to include pistol calibers. I know about some calibers already. .22 long rifle/ .17 HM2/ .204/ 5.56-.223/ .223, .243, .25 wssm/ 7.62X39/ 6.5 grendel/ 6.8 rem spc/ 9mm/ 40sw/ .45acp/ .50 beuwolf. I haven't seen others mentioned but know there are more.