So, what is the problem with locking back? Or, not locking back.

I know that if you use Ace mags that have the tab, you will damage
the Marvel unit. OTOH, if you dry fire, as in a sixth shot that is
not there, you can also damage the chamber(??).

So, the answer is to count your shots and stop at five! Gives you
something for your mind to do rather than think of a shot that may
have been out of the group. Such thoughts will (likely) cause more
errant shots. THINK POSITIVE! Let the functions of shooting the
shot be mostly automatic.

JMHO, dd