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Sevens · May 8, 2011, 09:24 PM

A comprehensive thread with a lot of good info...
One thing I haven't seen mentioned yet is pressure.

The .380 runs at a lower chamber pressure than the 9mm is designed to run at. The .380 runs at 21,500 PSI max while the 9mm is designed around 35,000 PSI.

A smaller case, as long as the bullet is the same bore diameter or smaller, isn't what you should put in to your pistol and it won't do your extractor any favors... but it shouldn't be specifically dangerous or threatening. (unless, as Jim Keenan pointed out, it ends up lodged in the barrel and a proper round is fired behind it)

The last example given of a .40 S&W in a 1911 chambered in .45 cal is bad, because the .40 cal is a high pressure round (35,000 PSI) in a pistol designed to run at 21,000 PSI. Not at all good! But in theory... the .40 cal round shouldn't have even gotten to a full 35,000 PSI because that pressure wasn't properly contained. Given the damage that resulted... not so good!

As a side example of what I'm saying... rifle shooters who play with wildcats do their share of fire forming. A wildcat to a rifle guy is a caliber (or more accurately, a chambering) that is not loaded by any factory ammo source. Instead, wildcatters must either buy brass that is formed to the spec of the cartridge and handload themselves, or they must form their own brass before they can even handload it.

Often enough, they will "create" the brass they need by fire forming, or shooting the parent case which is smaller than their chamber in their rifle. Many will make reduced loads with a faster powder to "blow out" the cartridge case to fit the chamber -- they do it with chamber pressure.

May 8, 2011, 09:24 PM	#17
Sevens Senior Member Join Date: July 28, 2007 Location: Ohio Posts: 11,755	A comprehensive thread with a lot of good info... One thing I haven't seen mentioned yet is pressure. The .380 runs at a lower chamber pressure than the 9mm is designed to run at. The .380 runs at 21,500 PSI max while the 9mm is designed around 35,000 PSI. A smaller case, as long as the bullet is the same bore diameter or smaller, isn't what you should put in to your pistol and it won't do your extractor any favors... but it shouldn't be specifically dangerous or threatening. (unless, as Jim Keenan pointed out, it ends up lodged in the barrel and a proper round is fired behind it) The last example given of a .40 S&W in a 1911 chambered in .45 cal is bad, because the .40 cal is a high pressure round (35,000 PSI) in a pistol designed to run at 21,000 PSI. Not at all good! But in theory... the .40 cal round shouldn't have even gotten to a full 35,000 PSI because that pressure wasn't properly contained. Given the damage that resulted... not so good! As a side example of what I'm saying... rifle shooters who play with wildcats do their share of fire forming. A wildcat to a rifle guy is a caliber (or more accurately, a chambering) that is not loaded by any factory ammo source. Instead, wildcatters must either buy brass that is formed to the spec of the cartridge and handload themselves, or they must form their own brass before they can even handload it. Often enough, they will "create" the brass they need by fire forming, or shooting the parent case which is smaller than their chamber in their rifle. Many will make reduced loads with a faster powder to "blow out" the cartridge case to fit the chamber -- they do it with chamber pressure. __________________ *Attention Brass rats and other reloaders:* I really need .327 Federal Magnum brass, no lot size too small. Tell me what caliber you need and I'll see what I have to swap. PM me and we'll discuss.