I know somebody who loaded and fired several handloaded .41 Rem Mags in a .44 Special Ruger Blackhawk. They keyholed into the paper target, which should have been the first clue. They were 230 grain Keith bullets and fairly long, and finally one of them was so long that it wouldn't allow the cylinder to turn another stop (it interferred with the frame at the bottom of the travel of the cylinder). The cylinder would back around part way but in the end the bullet had to be dremeled down in length to allow the cylinder to turn 360 degrees so all of the live rounds could be removed from the cylinder. But three of them had fired almost just fine. There is only .20 inches difference between a .41 (.410 inches) and a .44 (.430 inches).

Glad the OP posted his mistake. The moral of his story (and mine) is to check and double-check, and don't make assumptions...

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S&W Rover