|Andean carries AR15 upper receivers (semi auto only) in various calibers, such as .223/5.56mm NATO, 6.8mm SPC, 7.62x39mm Russian, and .300 Blackout. Manufacturers include DPMS Panther Arms, Bushmaster, DRD, CMMG, Advanced Armament Corporation (AAC), and Colt. Most of these fit the .223/556 MILSPEC (a.k.a. small hole, or small pin) lower receivers. Look at the product description for better details as to what features each has.