Either I have never noticed this before or have forgotten.  One of my Officers brought me his Colt AR-15 concerned that he would have a slam fire one day.  It appears that the firing pin is lightly denting the primer whenever he charges the rifle.  Several of the primers had very slight firing pin marks on them.  To me it doesn't look like enough energy could be imparted to fire the round...but.  Other than a titanium firing pin, anybody have an answer?

How often is he "charging the rifle"?

I thought the standard for carrying rifles was "cruiser ready". Empty chamber, magazine in, safety engaged.

The slight primer indent is normal. Unlike many other guns, the firing pin of the AR15/M16 does not have a rebound spring to stop it from travelling forward when the bolt slams forward.

yep, that's how they work.

The floating firing pin can't contact the primer until the bolt has cammed almost completely closed. This fact and the low mass of the firing pin (usually, normally)keep it from having enough energy to set off a primer. But one should always have the rifle pointed in a safe direction when charging anyway.

We do carry them chamber empty, loaded mag, safety on.  Depending on what part of town they work, the guys could be charging the rifle 2-3 times a week.  They have been reminded to get rid of the first two rounds in every mag regularly as they take a pretty good beating.  The primer marks may be a good indicator to rotate those rounds out.  Thanks all.