@KevinM shared this on his Facebook page. I know a lot of you don’t have Facebook, but this post is definitely worth the read.
You can see the whole article on Kevin’s page here: https://www.facebook.com/kevin.michalowski.uscca/
The general gist is that someone mistakenly put a 40S&W in a brand new 1911 chambered in 45ACP. The results were NOT good. While the gun suffered a lot of damage, the owner was luckily not hurt.
Gets back to what I said the other day and a few others did as well ‘Pay attention around firearms’ Maybe hobbies like Golf you can take a mulligan but you may not be breathing much more after you make a mistake on a range because you’re not paying attention to detail. This person was very fortunate to have escaped without injury or otherwise worse.
And here’s the “see more” information:
*"Valuable Lesson: Always be sure that you’re using the correct caliber ammunition for your gun. *
This was a brand new 1911 chambered in 45ACP. The owner grabbed a handful of ammunition out of an ammo can and loaded his magazine. He didn’t realize that there was a lone 40S&W cartridge mixed in with the 45ACP. The 40S&W was the last round loaded in the magazine so it was the first to be chambered. As 40S&W is smaller than 45ACP, it fell past the chamber and into the bore. Then a 45ACP was chambered and fired, which discharged the 40S&W lodged in the bore. The results were catastrophic for the gun. The owner is very lucky that he wasn’t hurt.
author unknown"
I couldn’t figure out exactly what had happened from photos. I am assuming this person chambered the 40 S&W, pulled the trigger, nothing apparent happened (firing pin pushed the 40 down the barrel), racked and chambered the 45, pulled the trigger, and it really went “boom”.
This is definitely a great reminder to be aware when loading magazines. I could also see this happening with a 9mm in a 40 S&W, etc. One would think somebody would notice the blunt end on a 40 if shooting FMJ, but could understand not noticing with JHPs.
.380 will fit in a 9mm gun. It just doesn’t eject well. No damage reported.
@Sneezy, I was editing that out while you were replying, I realized I had not thought that one all the way thru! 
if for some reason, the firing pin did do it’s job behind a 40…
Forty five ACP max pressure+P is 23,000 psi
Forty Smith & Wesson is 35,000 psi
or 240MPa to 140MPa
Essentially bigger number means the pipe and support assemblies need to withstand a much stronger force applied when the primer is activated and the propellent is ignited. Add, the misalignment of the 40 S&W round without good support on all sides means the brass casing is the only functional barrier to that pressure transient into the cavity created to hold the wider 45ACP. Also, there is a possibility for the smaller 40 projectile to yaw within the barrel and become wedged causing an additional blockage for the pressure being built up due to the expanding gases its another reason the under specification pipe and assembly could fail catastrophically.
About 20 years ago I was at a range where someone was firing a 10mm and a 45ACP from corresponding S&W models (steel). They looked the same. The person accidentally grabbed a loaded 10mm magazine filled with Corbon 135gr JHP and fired it from the 45. The first shot went through the target sideways. I went to the person and asked him to put the gun down. He knew something was wrong.
As he put the firearm down, the second 10mm cartridge slid through the barrel and onto the ledge. There didn’t appear to be any damage to the firearm, but I don’t know for sure. I don’t know if damage was found later or not.
@CHRIS4, so you are thinking it might have been as bad as a double whammy? The first being the 45 hitting the plugged barrel and the second when the higher pressure 40 went off, possibly cockeyed?
I would question the frame being bent, but using .40 in a .45 would cause a problem. Find it hard to believe it chambered and fired… or attempted to fire.
It sounds like (to me) the 40 S&W was pushed past the chamber into the barrel when the slide closed. I would assume the owner did a tap rack bang when the gun didn’t go bang, and chambered the .45 round. Then when he went to pull the trigger the 45 went flying into the unfired 40S&W cartridge in the barrel. From the bulge in the barrel, I would assume that the 40S&W cartridge went off/exploded.