Not having primers would be the only reason I’d do that. And the concern over FMJ bullets is well-founded, as to clean kills as well as safety.
Mule deer wrote a piece back during one of the Obama rimfire shortages that included recipes for .22 mag equivalent loads. Dig that up. I did pretty much the same thing with 4759 in a .223 long ago and far away.
Depends on what FMJ you have, but a lot will need decrimping of the primer pockets before the next go-round, which is why I studiously keep such brass in a separate, IN CASE OF FIRE, pile, hopefully to be left to my children, or theirs.
