From CMP's website:
You must provide proof of participation in a marksmanship related activity or otherwise show familiarity with the safe handling of firearms and range procedures. Your marksmanship related activity does not have to be with highpower rifles; it can be with smallbore rifles, pistols, air guns or shotguns. Proof of marksmanship participation can be provided by documenting any of the following:
Current or past military service.
Current or past law enforcement service
Participation in a rifle, pistol, air gun or shotgun competition (provide copy of results bulletin).
Completion of a marksmanship clinic that included live fire training (provide a copy of the certificate of completion or a statement from the instructor).
Distinguished, Instructor, or Coach status.
Concealed Carry License.
Firearms Owner Identification Cards that included live fire training.
FFL or C&R license.
Completion of a Hunter Safety Course that included live fire training.
Certification from range or club official or law enforcement officer witnessing shooting activity. A form for use in completing and certifying your range firing can be downloaded from the CMP web site at
http://www.odcmp.com/forms/marksmanship.pdf
No proof of marksmanship required if over age 60. proof of club membership and citizenship required for all ages.
NOTE: Proof of marksmanship activity is not required for purchase of ammunition, parts, publications or memorabilia.