There seems to be a common belief that the .22LR and .22 Magnum are like the .38 Special and the .357 Magnum in which the .357 is just a lengthened case and the .38 can be fired in the Magnum revolvers.
In fact, the .22 Magnum is NOT the same as a LR only longer.
The case is different, and the bullet is larger in diameter.
Shooting the .22LR in a Magnum gun will often cause split cases and can be quite dangerous.
If your friend is doing this, I hope he wears eye protection.