Just use A .22 CB, its a low velocity short, but way more power than pellet gun, it has almost a zero report.
The problem with this is, the 22 bullets ricochet all over, much worse than a pellet.
I have several pellet rifles, includeing Gammo and RWS... If i could only have one pellet rifle, it would be a RWS 45.... I've chronoedmine at over 900 fps with heavy pellets and over 1,000 fps with light pellets...
Thr CCI CB long or shorts do kill better than pellets, you just have to bemore carefull of ricochets when useing them.
The problem with 22cal pellets compared to 177 cal. is, the 22's are harder to hit with at longer ranges because they drop more...
DM