Loves me some 10mm, hate the .40.
Let me say first, I'm not a reloader. I have been told that there's no such thing as +P .40. Someone correct me if I'm wrong there.
But I've also been told that there's room in the 10mm loadings to safely run up the velocity a decent bit.
When I shoot steel plates with one of my 10mm guns, the plates react a LOT more violently over both .45acp & 9mm. In short, they're just wicked, wicked fun to shoot reactive targets with.
There doesn't need to be a +P .40S&W, it's already there, such as 165gr. FMJ-TC at 1,150fps making 484fpe - 9mm can't touch that. The 2015 politically motivated FBI decision to dump the .40 after a positive 28 year run was pure, near-post Obama DEI inspired. Even if the 9mm were any better, that only means the .40 is better still, and there was simply no practical, certainly no ballistic reason to squander billions of tax-payer dollars to drop the superior caliber for the lesser caliber. Of course we could not have known back then what we know today about what was going on behind the scenes in Washington.
The 10mm does NOT have a safety margin to run up the loads - I'm sure many have thought so and been disappointed the hard way! The .40 case is actually stronger than the 10mm case because of the small primer pocket, thus more meat in the base. The 10mm case is prone to significant bulging in barrels with inadequate chamber support, and this is an impediment to pushing the loading envelope unless you have a fully supported chamber. I have a LWD 5.2" 10mm barrel with a relatively tight chamber but still more exposed case over the feed ramp, and with hot Underwood loads on a hot day, cases kick out with quite a bulge and defined "smile". Eventually went back to using the OEM barrel with it's "looser" chamber - about the same lack of case head support under the reasoning that the loose chamber allowed the entire case to expand without focusing pressure on the spot over the feed ramp and it's true, cases from the Glock barrel never show the kind of bulge seen on aftermarket barrels with their "superior" tighter chamber! Barrel makers never show their chamber-ramp cut in photos, so buying one is always a crap-shoot - a major thing that soured me on the 10mm some years back. The way to make big power in the 10mm is by going to a longer barrel. A 6" barrel can often achieve 100fpe more than the stock 4.8" Glock barrel without more chamber pressure. Underwood makes such a variety of 10mm ammo for reasonable prices, that for those in States where they can mail-order ammo, just buy Underwood and call it a day.
As far as target reactions, the 10mm pales in comparison to the .460 Rowland capable of sending 230gr. slugs downrange at 1,400fps/1001fpe, and 255gr. at 1,325fps/994fpe. My Clark Custom .460 Rowland barrel has 100% chamber support - well, maybe 97%, but ample none-the-less. Due to being compensated, and now fitted with the V2 damper system, it kicks about like a .45 ACP, and uses a 9 pound recoil spring. I've run 185gr. "ball" loads over 1,600fps/1,051fpe. At that speed, don't even need an expanding bullet, the supersonic shockwave at legal bear defense distances is explosive!