I was a juror on a case where the hit weapon was a .22 Ruger with a catch bag for the brass and a large silencer. Easy fix; the bag was home made.
I have no personal knowledge but have read that at one time both the Mafia and Israeli intelligence agencies used the Beretta model 70 for killing. It is a light, handy and totally reliable automatic.
It is chambered for the .22LR.