I provided the following, and was approved on the spot -
- My DD214
- My club rifle qualification card
- My passport showing U.S. citizenship (doesn't have to be current)
- My Michigan CPL (also shows active weapons training)
- My birth certificate
I'm sure the passport and birth certificate were probably redundant. Better to have too much, than not enough.
Voter registration cards and driver's licenses are not valid proof of anything.