I have the stainless, CZ made one in .22H/.410
I benchrested it and got 1 1/2" groups and 1 3/4" groups with 45 gr. SP and 55gr. FMJ-BT reloads. To use .22H, you Must reload. Buy one huge batch of all the same make of casing.
My 55 gr. all-purpose reload goes 2,400 fps, in a Winchester casing, w/ 10.5 grains of AA1680.
If you can't hit anything with an M6, you are either a bad shot, or haven't gotten used to the "Law Rocket" style trigger bar. The military fieldmanual gives 50m as the max. "effective" range with the .22 barrel.
I can easily hit 2liter bottles at 100 yards with the .22H barrel. It shoots about as well as a match-grade pistol. With 700ish ft.-lbs. of energy, it is about like a pistol cartridge.
Rate of fire is low, as expected. But, it is a "survival" type of weapon. Mine is just about my favorite hunting weapon.
Not a "target rifle", or "assault rifle" but a "survival rifle." If you can only be happy with a high rate of fire, you won't like it.
On the other hand, if you expect one well-aimed shot to handle the situation, then this is a fine weapon.
Wish I had gotten one years ago. It often accompanies me on backpacking trips.
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I tried a fellow gun-owner's .22LR version, and I could hit coke-cans every time at 100 yards, with cheapo hi-vel ammo.