I was watching a Utube from the Military Arms Channel (MAC) guy (Tim I think?) and he is really a huge 10mm fan. He is not crazy about the 40 SW because it hurt the popularity of 10mm (he is mostly kidding). He did something in that video that is thought provoking. He shot some 40 SW ammo thru his 10mm semi-auto pistol and it seemed to function fine. The questions that hit my mind were: how are the 2 head-spaced and is that a problem? I’m guessing the extractor hook grabs both fine because ejection was good for both. The other question is about the “fully supported” aspects (or lack there-of) of both cases in the chamber? Is there a case bulging problem and is it safe?
At this point I would never do it because I am not educated enough to know if it is “DUMB”. However , Tim on MaC , seems pretty sharp.
What is the truth? My Dan Wesson Specialist owners manual specifically prohibits using ammo other than what is stamped on the barrel and that is what I will do.