OK..........½moa is a pretty small group at 100 yards with a rimfire.
I shoot rimfire competitively, and have several very accurate rimfire rifles.
[40X Remington, Annie 54, Suhl 150, Winchester 52, Remington 541 S&T, etc]
Now if we are talking 10 - shot 100 yard groups, I have reservations about some of the claims on here.
If we are talking 5 - shot groups, some reservations still remain.
If these are 3-shot groups, it is a bit easier to accomplish.
To shoot 10-shot, ½ moa groups at 100 consistently, your rifle had better be top of the class, ditto your ammo.
You will probably have a tuner on that rifle as well, and you yourself will be on top of your game.
Additionally, the weather had better be co-operating, because a zephyr of a breeze will take a shot well out of that ½ moa group.
Now if we are talking 50 yards, it is considerably easier to make ½" [not ½moa] groups, and there are a number of rifles capable.
At 50 yards, my best shooting 22 rimfires regularly group in the .125 - .175" area with ammo they like.
If the group is larger than .250", I know it is me or the breeze I didn't see.
Regards, Eagleye.