Originally Posted By: Plant.Onewith any rimfire ammo that's not "match" or subsonic, quality control is going to be the most common end to the accuracy discussion.
every lot is going to be different, and if you find a lot # that your gun likes, buy as much as you can find!
some lots will be very consistent and shoot well, others not so much
I can't speak to this on behalf of 22 WMR ammo, simple because I haven't done the testing with it like I have 17 HMR, but if it's anything like the 17 HMR ammo I've tested, and I have no reason to believe it wouldn't be, it can be alllllllll over the map.
I've had HMR ammo, from the same box of 50, chronograph with an ES of over 125 fps.
A couple years ago I weight sorted a few hundred rounds of rimfire ammo because I was curious what was causing these huge velocity spreads. After weighing them all out I took a couple of the lightest, heaviest, and a couple that weighed right in the middle, then carefully disassembled them and weighed out all the different components. The bullets all weighed the same, the powder charge all weighed the same, and the cases themselves were all pretty close to weighing the same. Nearly all the variance in weight came from the amount of priming compound in each case as there was over .5 tenths of a grain variance in the amount of priming compound in the lightest versus heaviest.
I have no technical data that says, how, the amount of priming compound they put in a case affects velocity, but it stands to reason, 1/2 tenth of a grain, more or less, of priming compound will likely have a pretty significant affect on velocity. Another thing I noticed when I bulled them apart was how much of the priming compound was smeared up the wall of the case on some, while others had it nearly all down at the bottom of the case.
I think it's really unfortunate they have rimfire cartridges that are capable of shooting much further than we ever considered rimfires capable of achieving, yet the manufacturers produce ammo with crazy amounts of velocity spreads.