O.K... here goes. Is the .22 LR reliable for SD. I think so. From about August 1979 up through April 1982 I carried a Ruger Mk. II standard type .22 LR pistol in the pocket of my work pants. I walked night security in a shipyard as well as a few other locals in New Orleans, LA. I have got no earthly idea how many rounds I put through that little pistol. Even on my limited budget (newly married student in seminary) I could afford enough .22 LR ammunition to shoot a lot. I got to where I could hit stuff fast w/ that little pistol. I can not remember that it ever failed to do anything but go bang when I pulled the trigger. It may be that I just bought super high quality ammunition. Maybe the humidity and high heat made the ammunition particularly responsive when struck by the firing pin. I don't know. I do know that that little pistol stayed in my right hand pants pocket every night, week after week. When I pulled the trigger, it always went bang. I don't know that I ever cleaned it more than a few times other than wiping the exterior off w/ a oily rag.
Over the last few years I've been known to slip my little 18-3 into my pocket, loaded w/ Mini-Mags. That little revolver has fired a wheel barrow load of ammo since the summer of 2000 when I bought it. It has not ever had a misfire of any sort. I shot a lot of CCI Blazer, Mini-Mags, etc. in it. I do clean it regularly. It is as tough as a tank. It has never missed a lick.
I do not doubt that there are problems encountered w/ rimfire ammunition. Doubtless there are some firearms and some brands of ammunition that are problematic, others are more reliable. Fired in the guns I own and use... Ruger Mk. II target competition model, S&W 18-3, S&W 15-22, Ruger 77/22, Ruger 10-22, Winchester 190... I have not found any problems w/ current .22 LR ammunition.
Currently I have a couple of nice revolvers in .38/.357, .44 Special, .45 ACP, any one of which would work very well for SD/HD. At night a 21-4TR is on the nightstand, loaded w/ some old (ca. 1971) Winchester 246 gr. LRN ammunition. Based on experience w/ ammunition from that batch, I am confident that if needed the ammo would light up and run just fine. I have .22 LR ammunition from a little later (ca. 1977-1980) that has proven equally perfectly reliable when fired in the 18-3 and Mk. II. It would be a sad thing if any of these pistols had to be used in a SD incident. But, if necessary I think any one of the three would be more than equal to the situation. JMHO. Sincerely. brucev.