.22Lr is hard to beat for cheapness. Love my 3” “Assassins” inspired MkIV
Just finished a F4 on a JK CX105 “solvent trap” kit they used to sale, it lives on my Gen 4 G19C and digs 165gr hand loads.
Most fun caliber personally is 5.45x39, using a F4 10” baffle can on it now but thinking about yarding the barrel off for a new 12.7” or slightly long for an AEM-5 set up.