Yes, you can shoot the LR in the Mag. cylinder/gun and its mostly unlikely any harm will come to you, however, as with anything that resides outside the usual norm, there are possible consequences.....you will probably get less accuracy than you'd like due to the fact that some mag barrels can be slightly different in diameter than the LR guns. Some use the same barrel as the LR guns, some don't, all dependant on the manufacturer. The higher the velocity on the LR cartridge you shoot, the more likely it'll split the case because the chamber dimensions on the mag are slightly larger, allowing for the brass to expand. Now, since the case may split, there comes the risk that a piece of the brass may leave the chamber and in what direction is anyone's guess. Extraction may be somewhat more difficult than normal and there's the chance that some of the brass left behind can end up in the chamber, bore and can fall into the action, causing problems with operation.
In a pinch, it'll work but wouldn't recommend it for more than a couple of rounds unless you're willing to risk the results.