It has to do with diameter. The .22 lr uses a heeled bullet so it has a smaller case diameter (.226") than the .22 mag (.242") so as mentioned above it may cause the case to rupture damaging the gun and the shooter.
Dan
You are correct about the different size case dementions,and the 22lr healed
bullet is .222 and the 22 mag .224. The healed 222 will swell and fit the
groves of the .224 barrel. I have an old H&R mod 676 that has a non recessed
cyl in 22 mag ,and will shoot cb,shorts,lR,22WRF,and 22 mags !
The swelling of the shorts longs or any of them come out with just a
push of the ejector rod.
This is a revolver and you cannot do this in an auto or rifle that the
chamber is cut for the 22 mag as the chamber will be too deep and the
firing pin will not hit the case.
But if you can find a non reccessed 22 mag cyl revolver ,then you have the
SHTF pistol because it can fire any 22 cal rounds you can find!
Bob