How about a Black Belt in Gunnery?
If you've put in the time (years) and earned your Black Belt, you can carry whatever the hell you want. Concealed handgun, assault rifle - whatever floats your boat.
We could do it by standard martial arts belt ranks:
White - has to pass written/oral safety test to advance.
Orange - BB gun, must demonstrate practical expertise in safety and handling to advance.
Yellow - pellet gun, must demonstrate expertise in marksmanship to advance.
Green - single shot .22 rifle or pistol, single shot 410 shotgun, must demonstrate expertise in powder cartridge knowledge, handling and safety, as well as cleaning and maintenance of powder guns to advance.
Blue - revolver, .32 or less, bolt action or lever action .22 rifle, 20ga. over/under shotgun, must demonstrate expertise in mechanical actions as well as safely clearing jams to advance. Highest rank that can be approved by a single Black Belt.
Purple - revolver any size, any size bolt, lever or pump action rifle, any single, double or pump action shotgun. MILESTONE: Demonstrated expertise in all basics. Eligible to instruct in basics under supervision of Black Belt. Must log 250 hours as basics instructor and pass a review committee of Black Belts to advance.
Brown - semi-auto handguns rifles, shotguns, 10 round magazine max, must demonstrate expertise in semi-automatic repeating actions, and also weapon control, safety and accuracy in single, timed and rapid fire WHILE UNDER STRESS, and pass a review committee of Black Belts to advance. MILESTONE: If 21 years of age, an carry, but NOT concealed.
Red - semi-auto, no magazine limit, MILESTONE: CCW. Must log 250 hours as intermediate instructor under the supervision of a Black Belt, and pass a review committee of Black Belts to advance.
Black - FULL AUTO rifle, pistol, shotgun, no magazine limit. MILESTONE: Eligible to be licensed as instructor. Must pass a peer review committee of higher rank Black Belts to advance.
2nd Black - sub-machine guns.
3rd Black - machine guns.
etc.
This scheme, A) does NOT violate the 2nd Amendment, B) insures adequate training, C) places the decision about who is responsible enough in the hands of others who are trusted at that level.
Perfect? Of course not. But a lot better. I mean seriously, how often do you see a news story about a Black Belt running wild? It takes dedication to reach that level, and if you are a nutcase, your Sensei, Sifu or Gunny is going to notice it while teaching you for a couple of years. This also avoids the slippery slope of creating a class of people who have been declared incompetent by some damned personality test.
So let's make Gunnery into a REAL martial art, get it recognized and sanctioned, and get the NRA to lobby the legislators to place the decision about who is qualified into the hands of the qualified.