SC4006, admitted 10MM fan here. I have owned quite a few 10MMs since my first, a Bren Ten, along about 1984. Gotta agree with Dan-O about most factory 10MM being not much different than .40 S&W. I have seen this trend toward loading down the Ten since the FBI's short lived adoption of the 10MM, and concluding that 180 grains at about 1000fps was the way to go. I can sure understand why some, especially younger, shooters wonder why the 10MM is worthwhile at all. At least a couple over the years asked me if 10MM and .40 S&W were actually the same cartridge. I used the difference between .38 Special and .357 Magnum to try to explain.
Anyway, I have owned the 10MM in both semi-autos and revolvers and consider it to be an excellent cartridge. In 5" barrels, the old Norma 200 grain actually did do 1200 fps, or a little over. The Norma is no longer available but some of today's smaller manufacturers still produce similar loads. The older CorBon 135 grain , since loaded down, averaged 1475fps in my S&W auto and 1585fps from my 5" S&W revolver. The Buffalo Bore 180 grain JHP averages 1380 fps in my 5" S&W 1026. These are velocities I've personally chronographed, not something that some guy in a gun shop heard from his friend's cousin, or read on the internet. The Glock 20 is not my favorite, mine was not the most reliable of 10MMs, but I can say it is durable and obviously holds a lot of ammo. Having owned the aformentioned Glock G20 and Bren Ten, Several S&W 10MM autos, Colt Delta, Kimber Eclipse, S&W 610 and Ruger Blackhawk revolvers in 10MM, I've come to favor the, unfortunately out of production, S&W autos. The several I have owned have just been good, solid, reliable, accurate and durable pistols. Most of the ammo used in them has been the "real" 10MM type, not the .40 S&W equivalent type ammo. Just never any issues. But, G20s are in current production, have a warranty and are highly thought of by many owners...ymmv
COTEP 640, NRA Life