Since I use a no name e-mail address I can't post on ar-15.com and ask them so here you go. I was wondering if anyone made a colapsable 4 or 6 position butt stock that worked on carbon 15's? I should get one in in a day or two but wanted to see if anyone knew of a problem with them not meshing. The guy at the local gun shop told me that it wouldn't work. I thought the carbon 15 lower was built to mil spec? Thanks for the help. Ted