A large SWAT team in this area had a failure to fire from an M4 with
Hornady TAP ammo during an entry––fortunately no officers were hurt and
the suspect immediately threw down his weapon when the carbine went
click instead of bang. After the incident was concluded, the team went
to the range and expended the rest of their carbine ammo and had one
additional failure to fire. This same team had 3 Hornady TAP rounds fail
to fire in training a couple of years ago. When Pat Rogers was teaching
a class at a nearby agency, there were 5 failures to fire using Hornady
TAP ammo. In all 10 cases, there appeared to be good primer strikes,
but no rounds fired.  On analysis, the ammunition had powder and checked
out otherwise.

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However, despite what appeared to be good primer strikes, two problems
were discovered.  First, when accurately measured, some of the primer
strikes had insufficient firing pin indentations. The failed round from
the potential OIS incident had a primer strike of only .013"—the minimum
firing pin indent for ignition is .017".  In addition, the primers on
the other rounds were discovered to have been damaged from repeated
chambering.  When the same cartridge is repeatedly chambered in the
AR15, the floating firing pin lightly taps the primer; with repeated
taps, the primer compound gets crushed, resulting in inadequate ignition
characteristics––despite what appears to be a normal firing pin
impression.  Once a round has been chambered, DO NOT RE-CHAMBER IT
for duty use. Do NOT re-chamber it again, except for training. This is
CRITICAL!!!