This brings up the question of what defines whether or not an individual is competent with a firearm. I'm thinking about my time in the Marines, and I can confidently say that your average (non-0311) Marine doesn't know a whole heck of a lot about firearms, at least not compared to your average "gun guy". A lot of Marines I knew didn't really know exactly what 5.56 meant and had no clue what sort of ammo they used, other than it was painted green on the tip. I remember one instance while deployed where I walked into the COC in the morning and the 3rd watch was having an argument over how many times the rifling went around in the barrel. They were holding the barrels up to lights and trying to count. No one, enlisted or officer, had ever heard the phrase "twist rate" and I actually had to explain it to everyone. Even I didn't know nearly as much about firearms when I was on active duty than I do now that I've been a NES member for awhile, and I was considered the "gun nut" of my platoon because I had a real LTC.
Now, that being said, only 2 or 3 guys in my platoon didn't consistently shoot expert on the range. All of us has been through shoot houses and combat marksmanship training and force-on-force with simunitions and all sorts of other training. We all knew a great deal about how to use our issued weapons, and performed very well with them. So I guess a good summary question would be, if you can safely and accurately employ your issued firearm, does it really matter if you don't know that 5.56 is a metric measurement and .223 isn't?