It has always been so. In loading the rimfire cartridge, the liquid primer is dropped in to the case and the case spun to distribute it around the inside of the rim. The possibility that it may not be well-distributed is very real. But also, the firing of the round requires the case rim to be crushed, and this takes more hammer energy than a CF primer requires. This is the reason small .22 revolvers often have such heavy triggers -- a heavy mainspring is mandatory for reliable ignition. Considering the billions of .22 rounds loaded, and the inherent problems of loading reliable ammo, it's amazing that inconsistent ignition isn't a bigger problem than it is.

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Pisgah