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Easiest one is the second stock/action screw, if it doesn't have that already.
Escutcheons are another fast upgrade...gives you more consistant stock/action mating.
And most of 'em love a good trigger job, if the previous owner didn't already take care of that.
Takes about 30-45 minutes the first time, 10-15 min after you get used to it.
The newer .22 WMR ammo has a lot better speed than the old, so you get to use everything from 30-grain to 50-grain bullets,
from 2300 FPS (30-grain) down to 1530 FPS (50-grain).
New Hornaday Ammo expected soon is suposed to be even faster