I bought a used .22 mag barrel single shot barrel for my Contender G2.
There was a thick ring of lead at the far end of the chamber. Someone had been shooting .22lr in it and the bullets were being stripped of lead when they tumbled into the end of the chamber.
So it was firing, and lead was coming out of the barrel, but I don't consider that to be working.
I have wondered if in a pinch (emergency) you could take empty .22 mag cases, cut the rim off, slip a .22lr into the end of it and shoot it from a .22 mag chamber. The mag brass would guide the bullet and prevent gas from passing the bullet.
FWIW, the .22 mag case is not tapered, it measures .238" - .239" from stem to stearn.