The cartridge on the left in picture one is a 9mm Luger that an IDPA 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.
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