Originally Posted by cycloneman
i have shot 40's in my 10mm autos.
Consistently? Magazine after magazine after magazine? I can think of two ways that a 40 would fire in a 10mm.
Either it was seated all the way forward, so that the round was headspacing on the case mouth, leaving a massive amount of space behind the case, and the firing pin was long enough to reach over that distance and fire the round. This would batter the case and be hard on the gun.
Or it was held back against the bolt face by the extractor hook. This should fire, but I wouldn't think it would have the force to work the slide.
I fired a 380 in a 40 S&W one time. One time. A friend of mine fired 5 357s in my Ruger Super Blackhawk 44 magnum, once. Once.