This originally started as a response to Chriscscs's thread on "Why I gave up on Glock 20" but since it turned into a Russian novel, I thought I'd give it a seperate thread.
I'm a big fan of the 10mm cartridge, and have to reluctantly agree with your conclusions.
The biggest enemy here is the idea of "Norma Spec" ammo. The original spec called for a 200 grain FMJ-FP going 1200 fps, and a 170 grain JHP going 1300 fps. That was out of a 5" pressure test barrel.
Everyone is stuck on the idea that if their ammo doesn't go that fast out of a 4.6" Glock barrel, "it's just as weak as .40 S&W." I'll get to that idea in a second, but the reality is, those velocities are pretty hard to come by with the Glock 20, particularly with the 200 grain bullet. There is no load data in a reputable loading manual that will get you going that fast out of a 4.6" Glock barrel
I've been a 10mm shooter and hand loader for over 15 years, and have launched many thousands of rounds out of three different generations of Glock 20's. They will run with 200 grain bullets in the 1000 to 1150 fps range quite well, with a two handed grip, one handed grip, firm grip, weak grip etc. Once you start pushing past that, the wheels fall off. It's a very nonlinear response in that you can work up a load that is 100% reliable at 1150 or so, but once you push past it the gun starts having frequent problems.
Many folks respond by adding a heavier recoil spring. This often causes more problems than it solves. It doesn't do as much as they think to retard rearward slide velocity, but does increase forward slide velocity, giving the magazine even less time to push a heavy column of bullets upwards to present the next round to be fed into the chamber.
This is one area where hammer fired guns have an advantage. Hammer guns can be tweaked by changing the mainspring rate, which does affect rearward slide velocity (but not forward) and by altering the geometry of the firing pin stop.
The Glock 20's problems are exacerbated by trying to feed it heavy, wide meplat lead projectiles. The gun was never designed to feed these projectiles. Most loads are going for nuclear speeds, so they are loaded long to keep the pressures down. Depending on the bullet profile, this results in the edges of the bullet rubbing against the sides of the magazine where it tapers in towards the front.
I have always been able to get my glocks to run reliably with 200 grain bullets in the 1100 fps range, and 180 grain bullets in the 1200 fps range.
As an aside, there is some goofy ammo out there for the 10mm. I feel there is very little reason to carry 10mm solely as a CCW cartridge, but people insist on doing it anyway. I would strongly reccomend avoiding loads that use jacketed hollow points designed for the .40 S&W pushed to 10mm velocity. For example the 180 grain Speer Gold Dot is an excellent bullet, particularly with intermediate barriers, when used within its design parameters, but pushed to 1300 fps it will fail.
Why bother with 10mm? First, the 200 grain bullet is truly "heavy for caliber" in that it has a sectional density equivalent to a 255 grain .45 ACP load. I've been well pleased with the 200 grain Hornady XTP at this velocity as a "trail gun" for the lower 48. Is it a death ray? No, but I do think it offers some advantage. The XTP is getting long in the tooth, and I'm excited about Speers new 200 grain Gold Dot, as we will finally have a modern, bonded bullet that is designed specifically for the 10mm.
Second, I've tended to treat my 10mm as a modern day equivalent to a .357 revolver. Many people carried .38's or .38 +P ammo in their .357 revolvers, and loaded up with Rhino Rollers when they headed into the back country. While my primary "town gun" is a 9mm, I often find myself with the 10mm as we travel back and forth on our back country outings, passing through small towns, highway rest stops, and gas stations and such. I'm perfectly fine with .40 Smith and Wesson power level ammo in these settings, and in fact prefer it.
So my current practice is to carry the 200 grain XTP handload in the back country. This likely will get replaced with the new Gold Dot load. I've tested the 175 grain Hornady Critical Duty load, which is a sort of hot .40, and like it for "town-ish" carry. I feel that either load is sufficient for black bear, cats, and my biggest threat in the back country: crew cab pickups full of tweakers.
I'd encourage the original poster to consider the new 10mm Gold Dot load. The ballistics aren't as sexy as some of the nuclear loads out. High velocity numbers sell ammo, but I really question whether it gets us anywhere. Early reports from people with chrongraphs shows the round is running in the high 1000's to low 1100's, which is the sweet spot for reliability that I've found. I received an email from Speer saying it runs towards the long end of penetration at 15".
The open question for me is can I get the G20 to run reliably with 200 grain wide meplat, hard cast lead loads? I suspect I can, but they won't be running at 1200 fps. I'd be happy if I could get bullets like that to run anywhere over 1000 fps.
I think once you get a 200 grain bullet going in the 1000 to 1100 range, there is very little to be gained by pushing it up above 1200. At 1100, you're still measuring penetration in feet, not inches at that velocity, and it should be sufficient to bust a thick heavy animal skull.
So my quiver for the 10mm will look like this:
* A "townish" load, at .40 or hot .40 levels. Currently this is the 175 grain Hornady Critical Duty.
* A "backcountry" load that is currently a handloaded 200 grain XTP going 1140fps. This will likely soon be replaced by the 200 grain Gold dot.
* A yet to be devleoped 200 grain hard cast load.
With the advent of the factory 200 grain Gold Dot, the "Townish" load becomes optional. I'd some concerns about carrying handloads in an area where a self defense against people situation is more likely than animals, but the factory Gold Dot neatly solves that.
The hard cast load will likely be a handload. I've poor experience with the factory offerings.
Prior to learning of Mr. Sundies poisoning proclivities, I tried some Buffalo Bore hardcast. They ran, with a hard two handed grip, but were a train wreck with a weak grip. I shot a small amount of Underwood, but terminated the test after examining some fired brass, as I value having ten functioning digits and two working eyes.
It think the key with the 10mm is to be happy with an increased bullet weight and velocity out of a service sized pistol, but not try to turn it into a magnum revolver. A 200 grain bullet at 1100 is a step up over a standard service cartridge.
The optimal solution to the "Field Pistol" may be the HK USP in .45 Super. I'm heavily invested in the Glock platform, so I'll likely stick with it. BUt if I were presume to give advice to someone who 1) Didn't mind that particular platform and 2) wasn't a handloader, I'd probably steer them in that direction for a back country pistol.