The only "RUGER" only loads I know of in .44Magnum are those which have TOO LONG a bullet to fit S&W cylinders, but will fit in the longer SuperRedhawk cylinder.
IF you are talking about those loads, you really need to examine the rifles, carefully, WITH the ammo inhand. Some lever guns, particularly Marlins are very sensitive to length.
I can see a possibility that a load with a heavy (300gr) bullet could be too long to properly work through the feed system of a lever action.
I KNOW 210gr .38cal bullets can be loaded too long in the .357 to work through the Marlin action, a friend of mine did it, jammed the gun, and brought it to me to fix.
I don't know about other makes of lever gun but I suspect they also have a min and a max length that they will run reliably.