I just traded into a DPMS (unsure of exact model number). It has the fixed A2 style buttstock and a free float rail-less fore-end and rear night sights. I'm wanting to mount one of the Magpul buttstocks or possibly a Vltor. The question it creates is do I need a .308 specific buffer tube or can I just purchase the .308 specific buttstocks and be good? Any help would be awesome, Thanks!