The problem with rimfire reliability seems to be the alleged claim that rimfire primers are more liable to oil contamination than centerfire primers. That said, the only round I ever had truly get messed up from penetrating oil was a centerfire 9x18 Hornady.
But rimfire weapons DO seem to be far more particular about their kind of fodder. I've even seen where two instances of the same make and model were more reliable with different brands of ammunition.
My own current Black Widow has been 100% reliable with CCI Maxi-Mags. But when I tried CCI's TNT HPs, two out of five cylinder holes consistently needed repeated strikes. Looking at the two different rounds, it was easy to see that the TNT had a visably thinner rim than the Maxi-Mags. Apparently in my gun, at least, that meant those cylinder chambers had just enough play to make the hammer strike unreliable.
However, good rimfire ammo which I've tested at the range with various .22 handguns for a couple of hundred rounds has proven to be as reliable as center-fire -- provided I didn't drench the gun in something like Hoppe's Benchrest and then throughly remove the excess (that's what happened to my Makarov. Benchrest really is penetrating, and the excess totally messed up the Hornady ammo in the top of the magazine).`