Originally Posted by frazod
I think my next major investment for the AR will be a .308 upper.
I 99% sure you need a AR-10 lower unless you are talking 7.62x39.
At least, that was a few years ago. My dads .308 AR-10 doesn't mix with the 15's we have.
Can I Use a .308 AR or AR-10 Upper Receiver on an AR-15?
NO, The lower receiver is not large enough to accommodate the .308 Winchester/7.62x51 Cartridge. If you wish to operate a .308 diameter cartridge from an AR-15 platform I suggest the 300AAC Blackout.
Of course, knowing your taste you probably already have the required equipment.