CMP guns can only be sold to members of CMP-affiliated clubs who are also U.S. citizens, over 18 years of age, and who are legally eligible to purchase firearms.
The purchaser must provide proof of age, proof of citizenship, and a copy of a current club membership card. A national NRA membership doesn't qualify.
For every single gun sale, the CMP must complete a background check on the purchaser, which must be approved by the FBI. For people living in most states, this is more involved than buying a gun from an FFL.
The purchaser must provide proof of participation in a marksmanship related activity or other wise show familiarity with the safe handling of firearms and range procedures.