tried out a barrel tuner today the inexpensive rubber one.

Compared two brands of 22lr shot both with out the tuner (100 yards) - installed the tuner and shot my ammo of preference .
- did some adjusting finally the best grouping with tuner about 6 inches from the muzzle . Tuned he gun with screws set at 20 pounds -
I tightened the screws and the grouping did spread out.
Went back to 20 pound setting and group tightened right up .
Then shot the other ammo with the tuner set for my preferred ammo - the grouping was worse than when I shot it with
no tuner .
Tuner does have a effect on the tightness of your grouping - for 10 dollars worth a try. Gun a B22 bull barrel plastic stock / 4x16 Weaver scope
not a world beater but fun to shoot.