[punch line from old joke]Don’t worry it will be there[/PLFOJ]
For decades the question was “Colt, or S&W” as most PO’s carried either brand in a 4" bbl .38spl revolver. No longer. 9mm is popular, as is .40cal,and even .45 and .357.
Note that during the last decade of revolvers, many dept carried a .357 revolver, but never .357 ammo. They used .38spl +P+. Now in reality, the .38spl+P+ load is no different than many .357 loads, but the perception was there.
On preview, I see that Stranger On A Train has pretty much answered this question.
TheLoadedDog "New South Wales police carry a Glock .22 " .22? Are you sure? I have never heard of a PD carrying .22 “long rifle rimmed” as a duty gun. (In S.America, they had a carbine chambered for .22WMR issued to some paramilitary forces)
Likely he means a Glock Model 22 (full-size frame chambered in .40 S&W). Glock doesn’t make a rimfire (.22 LR or .22 WMR) firearm.
Stranger
That makes much more sense. Thanks. 
Does Glock make an insert allowing .22 to be fired for practice? 
No. There’s no practical way to make a centerfire gun shoot rimfire cartridges with the same action. There are a number of swap out kits that comprise a new barrel, slide, guide rod, spring, and magazine, most notably for the 1911 and Browning Hi-Power (and I see that Ciener makes them for the Beretta 92 and Glock 17 & 22 as well), allowing you to shoot .22 LR, but this is far more than adding a simple barrel insert.
Stranger
::: cough:::
Heckler & Koch HK4
::: cough:::
Swap the barrel, new clip, and flip the firing pin over, and you were good to go.
“They call me MISTER Gibs!”
I knew I was forgetting something, and I even thought of the HK P7K3 (which fires .32ACP and .380ACP interchangably, but requires a different slide for .22LR) but totally missed the HK-4. Why you’d want a gun that can interchange the .380ACP–a passable round–with two of the most useless calibers known to man is another question about which I don’t care to speculate, but nonetheless I recognize your firearm-trivia superiority.
Stranger
I learned from another board that many cops do indeed carry a revolver as back-up. There’s still a little distrust in the reliability of semis. Especially among old timers, I guess.
There’s a professional shooter, I don’t remember his name, who can empty a six-shooter as fast as or faster than most shooters with semi-autos.
He may be on youtube. It’s pretty amazing.
Peace,
mangeorge
Yeah, here it is.
Kinda cool. 
By the way; I do know that capacity, not speed, is one of the charms of semis.
I use a .22 kit for my 1911, and yes it is more than an insert, but that is the term they used when they sold the entire kit to me.
Why would someone want .22? One of the cheapest rounds out there and you can practice in your basement- assuming local laws, safety,etc etc etc, IANAL, YMMV, etc etc.
Actually, all the cops I know carry for it a much different purpose: So if their main piece is taken/lost/out of rounds, they’re not SOL.
My buddy that had one just had the .380 and .22 barrels for it. Plink all afternoon for $1.50 then switch barrels for keeping the gun around the house.
Really brought the price for practice down.
I agree with you on the other two calibers.
That’s why they they carry a backup alright, but is it a semi or a revolver? I don’t know personally, I’m simply repeating what I read on a (cop heavy) gun board.
Also, many sites I visited when considering a defense gun advised a revolver and training. That is, if not a shotgun.
I do know my tricked out semi-auto .22 does rarely jam. With a revolver, if you get a ftf you can just go to the next chamber. A semi you have to clear. With a shotgun, the pump has the same advantage over an auto.
IME, they’ve generally gone with a revolver because of the smaller size, not because thy think they’re more reliable.
Yeah, I was referring to the .25ACP and .32ACP…rounds that are almost as expensive (sometimes moreso) than a full size centerfire caliber, and with little utility in defense or sport shooting.
Despite the claim that “revolvers don’t jam,” I’ve seen plenty of them jam after getting just a little bit of contamination wedged between the frame and cylinder, or due to a bent extractor rod, or a loose moon clip, and so forth. They’re also rather fragile in comparison to most automatics. It used to be true that concealably small automatics were chambered in puny calibers (like the above mentioned .25 and .32), using straight blowback action, and were not reliable, whereas you could buy a lightweight J-frame-size revolver that would permit you to carry .38 Spl or even more powerful rounds like the .357 Magnum (Ruger SP-101) or .44 Spl (Charter Arms Bulldog). In the past couple of decades, however, many manufacturers (Glock, Para-Ordnance, Springfield Armory, Walther, Sig-Sauer, Kel-Tec, Kahr, Beretta, among others) have come out with subcompact versions of large bore automatics using a mechanical lockup (typically the Browning linkless style lockup) that are more compact than a snub-nose revolver, have a longer barrel per overall length, and are reliable with a wide range of ammunition. It’s true that a dud primer in an automatic requires a “tap-rack-bang” drill rather than just pulling the trigger, but this is so rare in quality ammunition–back when I was shooting regularly I never had this happen except on one occasion with corrosive primer Egyptian ammunition–that it’s not a significant concern.
Regarding pump action shotguns it’s a common occurance for someone not well-drilled in the function to “short stroke” (not fully extend the forearm after cycling the action) the gun and not properly chamber a round. I don’t have much experience with autoloading shotguns so I can’t really say firsthand what the reliability those are, but I’ve seen plenty of people fail to properly cycle a pump action, which gives lie to the common notion that one need not train or practice with a shotgun. I think in large measure the reason pumpguns are most favored is because they are significantly cheaper than autoloaders and do not need to be adjusted for the use of different rounds.
Stranger
Around here, all the cops carry pistols, and the shotguns are all pumps. I have no idea about their back-ups.