Naturally, being the smaller round - a .22LR 'will' fit into a .22 Magnum cylinder.
There's usually enough rim for the cartridge to be supported and it will 'probably' fire when struck by the firing pin if that's the case.
Don't do it.
It'll likely split the case mouth, if not the entire case as the walls expand to fit the inside of the cylinder.
You'll know if that's the case, as you attempt to extract the fired cartridge...
Look inside the cylinder and you should be able to see a slight taper and a slight 'ring' where the longer .22 Magnum extends.
Shoot those and you should be fine.
One of the problems with buying imports is that sometimes, a few quality control steps get missed - like proper markings and/or both cylinders being shipped.
Good Luck!
Vaya,
Scouts Out!