i have a few inserts, the ones that have a .22 bore, just use a dummy case in the chamber, to support a .22 lr cartrige, and they work pretty good! i have .22 to .22 k hornet, .22 to .222 rem and .22mag to .222 rem. the hornet and 22 to .222 rem work great! very accurate!
one that i have from hammond enterprises ltd. is for my 6.5x55 swedish mauser. it,s a little diffrent. you have a chamber case, that holds a sized .270 round ball, in the mouth end,and a .22cal, blank in the back end. the blank powers the round ball! blanks come in diffrent power levels. the lowest power blank will kill a rabbit or squirrel, with no problem. its pretty accurate, one inch out to about 40-50 yards, and very quiet!
i read an ad about a set up that uses lead cups, over a .22lr cartrige, to fill the gap, between .22 and whatever bore size your using. i dont have first hand experience with this set up. but from reading about it, decided that the accuracy was not that good.
i love to play with them, in reduced power form.
what calibers do you need adapters for?
good luck!
coopershooter