Actually, many older .22 Hornets (and K-Hornets as well, I suppose) have bores of 0.222-0.223", so, that may not be a problem.
If it IS largish, then .22 Mag, might do for a conversion, but it seems a complete waste of effort at that point!
Besides, it would be easy to swap back, and you would have a bolt assembly. for a dedicated .22 lr that could be done for cheap, if you have a .303 w/ a bad barrel or some such.
Or just do custom reloads as stated above (subsonic loads anyone?), whatever, as long as you shoot the dang thing!
(Can't abbreviate "assembly" for some odd reason....)