
A great many competitors
often have pistols of different calibers and normally that is no issue unless
you fail to segregate your ammunition. I frequently see competitors in local matches
shooting two guns, each one a different caliber. It is not uncommon to see
competitors loading and unloading magazines as they switch pistols during a
stage. This is one instance where the potential for a problem creeps in because
competitors occasionally mix calibers in this process—at times with disastrous
results.
The cartridge
on the left in picture one is a 9mm Luger that a competitor loaded in a .40
S&W magazine. It then chambered and fired in a Glock 23 with essentially no
problem other than failing to eject. The cartridge on the right is a .40
S&W that a competitor unintentionally chambered and fired in a 1911 .45
ACP. Once again, essentially no problem other than failing to eject.
The center
piece of 9mm brass in the picture has an unusual characteristic. Can you spot
it? The center 9mm has rifling marks. I was a Safety Officer during a Pistol
Caliber Carbine (PCC match when a competitor who was shooting a .40 S&W
carbine had a “click” when he expected a bang (I forget the model—not an AR
platform). He retracted the bolt and nothing ejected so we both assumed he had
a failure to feed (he had just inserted a new magazine). Tap, Rack and the next
round fired; however, now he had a failure to eject. As he retracted the bolt I
saw shiny metal slivers spilling out of the ejection port.
Upon seeing
this, I stopped him and had him clear the carbine. As I examined the ejection
port I realized the shiny slivers were remnants of a .40 caliber bullet. I
dropped a rod down the bore and there was an obstruction. We tapped the
obstruction out and discovered the 9mm brass you see in the picture. He had
loaded a 9mm round in his magazine and when the bolt when forward I believe it
pushed the 9mm cartridge into the carbine’s bore. At least when he chambered
the next .40 S&W round it fully seated and fired. The .40 bullet struck the
9mm round which then fired as well with the 9mm bullet exiting the bore. The
.40 bullet destroyed itself when it hit the 9mm cartridge.
The rifle was
undamaged. The competitor checked his magazines for any additional stray 9mm
rounds and finished the match. I suspect that the competitor was lucky in that
the carbine he was using was strong enough to deal with the .40 S&W’s
pressure.
Shooting
ammunition in a pistol or PCC that is not designed for that particular round is
dangerous and can result in catastrophic damage to the firearm and potentially
serious injury to the shooter or bystanders. Using the wrong ammunition can
result in the release of high-pressure gas in a pistol's barrel, chamber,
and/or action that exceeds the design specifications for that particular
pistol.
To be safe,
you should use only ammunition of the caliber the firearm manufacturer
designates for that particular firearm. Every modern firearm has markings
indicating the correct caliber or gauge of ammunition to be used in that
particular firearm and these markings are usually found on the firearm’s
barrel, frame, or receiver.

One way to
verify that you are using the correct ammunition is to check the head stamp on
the ammunition to confirm that it matches the caliber or gauge that particular
firearm is designed to fire. Some types of ammunition (typically military
ammunition) do not have stamp markings on the head of the cartridge. In that
case, check the original ammunition packaging to determine its caliber.
If you have
any doubt about the caliber of the ammunition, you should not use the
ammunition until you have it examined by a qualified person who can determine its
caliber. Remember just because a round of ammunition can fit into a firearm
does not necessarily mean it is designed for or safe to fire in that
firearm.