Freedom-15 AR15 100% Lower - Question and Answer of the Day. Question: What caliber can be used besides 233/5.56? Is it possible to use 300aac, 6.8 or 6.5? AR15mold.com answer: The short answer is any caliber that works on a standard .223/556 AR15 lower will also work on the Freedom-15 AR15 lower. Some of the calibers that will work with the Freedom-15 AR15 Lower Receiver are: .223/5.56, .22, .204 ruger, FN 5.7, 6.8 spc, 6.5 grendel, 6.5 AR, 6.5 PPC Improved, 5.45x39, 7.62x39, 300 blk out, 458 socom, 45acp, 9mm & 7.62x25 The complete list of of compatible calibers goes on and on....including: wssm, rifle, and pistol calibers. If you have any more questions, please let us know. Thanks, Staff at Ar15mold.com #freedom15 #ar15mold #ar15news #ar15porn #ar15question #ar15build @ar15mold