In 1985, Irving Stone made a run of barrels for Colt in 10mm. He sold me one of the over-runs. He also pointed me to to Huntington Die Specialties for a die set, which they made up for me. It was marked "10mm Bren". Speer had one, and only one box of 10mm pistol bullets. Irv told me that they were able to modify the Wilson magazine to feed the 10mm "ok". With that, the project was on.
I opened up the breech face of a 38Super Colt slide, fit the barrel to that slide and an existing frame, and loaded up some test shots with Blue Dot starting with 38Super load data (oh heck, there was nothing on the radar for data in those days). Things worked, but it was sort of anemic.
Two things happened when I loaded up a little warmer. First, the Wilson magazines needed more tweakage, and stronger springs. What was happening is that a loaded cartridge would fly out of the ejection port along with an empty. Sometimes, the next one in the mag would feed, but usually not. Second, I started to consider slide velocity. Conservation of momentum being what it is, I considered ways to add weight to the slide. My solution was one of those "barrel bushing" comps, which really are nothing more than weight on the slide. I forget who made it. Probably Wilson. Its weight was a near perfect offset to the added slide velocity that otherwise would have occurred. Hot 10mm, cartridges now resulted in the same slide velocity as the 45ACP. And yes, I had a 10mm "Government Model" before Colt released theirs. Nobody calle 'em 1911's back then.
So why the story? Because I don't think anyone has really devised a good 10mm handgun yet. Double springs, flat wound springs, buffers and gizmos don't really and fully overcome the obstacles, nor make for a handgun that will have really great life expectancy.
Therefore.... 10mm in a handgun gets no nod of tacit approval from me.