Fresnel
it's really not that hard to figure out when your gun isnt going bang anymore, thats not the point of having a bolt hold open anyways.

Did I fire 6 shots or only 5? Doesn't matter. It's a 7 shot revolver b***h. BANG!
Having not been in a fire fight I'm not sure how easy it is to keep track of rounds fired on a semi auto, but whenever I go shooting it's pretty easy for me to keep track of my shots fired.