The XDm and the SR45 give full support of the case-head and they share something internally that I highly favor in a poly-frame pistol: the removable steel camblock with integral slide rails. I believe the S&W M&P also has a steel camblock while a number of others, i.e. Glock do not. This system, as far as I know was first used by SIG/Sauer with the alloy framed P-22X series.
IMO, the SR45 and XDm are the best of the bunch when it comes to full size poly frame, striker fired .45 ACP pistols. I like having the assurance of a manual safety a bit more than the XDm's grip safety. All of these pistols have a striker safety that prevents the striker pin from contacting the primer if the trigger isn't fully depressed.
The magazine disconnect is pretty much a non-issue. If you like it, leave it in. If you want to decrease trigger pull weight somewhat, and as mentioned, it's easily removable and only takes a few minutes to have the SR45 back together again. I like both pistols very much, but because the SR45's manual safety being something like a 1911, along with it being the trimmest poly-frame double-stack, I actually sold my XDm 4.5 in .45 ACP right after the SR45 was introduced and I bought mine in April of 2013. The XDm was sold to my shooting partner who later sold it. A move he now regrets with open carry being on the table in Texas, where our new governor has already stated that he will sign it into law if passed by the Texas legislature.
In regard to chamber support specifically, a pistol is considered to have full support of the case-head when none of the case forward of the extractor groove, or very little, is exposed over the feedramp. With the .45 ACP only being a 21,000 PSI cartridge, I never expected to hear of a Ka-Boom, not even the G21 yet they have occurred where opinions on why vary. In the case of Glock .40 S&W pistols, if you check hard enough, you will find that there have been Ka-Booms with factory ammo and we had one such event reported by the former owner of our local gun club/range with a new G22. It was a few years back and Glock has tightened chambers. I'm not much into the .40 S&W anymore, but I'd never own a Glock chambered for it regardless of the slight improvements. Glock has always used the loosest tolerances in their chambers to aid feed reliability. It's a shame because the G21 is a good pistol otherwise and pretty soft shooting. But, like one well known pistol instructor and an obvious Glock fan states, "All pistols should be Glocks, and all Glocks should be 9mm." The second part he got right.
Considering the structural strength of the SR45, its inherent accuracy and excellent adjustable sights, even in my large hands I still prefer its more natural feel in comparison to the XDm. If that's not an issue for you, you won't go wrong with either pistol and improvements can be nade to either's factory trigger like the PRP kit I installed in my XDm, but with pull-weight reduced to between 3 & 3.5#, I felt more comfortable with it at the range and prefer the SR45's manual safety for carry, and mine is as accurate as my shooting partner's DW CCO and he'd be the first to tell you that, and my handloads are fired from both pistols. :wink:
For Sale WTS Remington 870 Express 16ga 28” Remchoke Shotgun