I did exactly that once by shooting both .40 and .45 pistols in the same range session without removing all the .40 ammo from the firing position before switching calibers. I mixed a .40 in with .45's and it chambered and fired in a Kimber Ultra Carry. Because the .40 case has a smaller diameter than the .45 and the projectile was too small to engage the rifling in the bore, it simply made a "pop." The projectile did exit the bore, but with much reduced velocity, and the case was found to be expanded to the size of the .45 chamber. There was no case rupture or damage of any kind to the gun because the result was actually a low pressure discharge (due to the fact that the case was not fully supported by the chamber at the time the bullet was ejected from the case).MojoTexas wrote:I was at the range today, breaking in my new Kimber, and I was digging through a bunch of loose rounds in the bottom of my range bag looking for more .45 ACP to shoot. I might add that I own and shoot a LOT of different calibers, including 9mm, .357 magnum, .40 S&W, and .45 ACP. I had started reading this thread a few days ago, and as a result I was extra careful to look at the bottom of the brass to make sure each round was .45 ACP. I was scared to death I would accidentally load a .40 S&W round into my brand-new Kimber and have a "kaboom" situation since the .40 S&W has a higher pressure than .45 ACP. Needless to say, it was all good. :-)
That being said, it's obviously not something you want to repeat yourself. The results might not be as benign.
Under the heading of not making the same mistake twice because of all the new ones available, I now either remove EVERY round of one caliber from the firing area before I switch to a gun that fires a different cartridge, or I segregate each gun /ammo combination to opposite sides of the firing point table (2 maximum) and keep loose rounds confined in a box or bag of some kind to prevent intermixing.
