Someone came by looking for “.41 Long Colt .41 Magnum compatibility.” Those cartridges are not in any way compatible.
Starting with the smaller, the “.41 Long Colt” is another of those low pressure 19th century caliber oddities. Where most .38′s and 9 mm cartridges are actually .36′s (.356 or .357 bullet size) the “.41 LC” is actually a .38. I have seen some badly worn bores that slugged as large as .386, but most are actually close to a true .38. A .41 Magnum cartridge should not fit the cylinder and if you manage to shoehorn one in, you would be holding a bomb in your hand.
If you have an original .41 Colt revolver, you would be better off cleaning it carefully and putting it up. They are worth far more as antiques than as shooters. IF you must – original LC cases, loaded with five grains of ffg black powder equivalent and cast “heeled” bullets of a design made for the cartridge will do for a demo. Wear eye and hand protection while you are doing that.
The .41 is a true “four ten,” with a bore 410 thousandths of an inch in diameter. You might get some Long Colt Cartridges to fire, but they sure would rattle going down the barrel. And .41 LC cartridges are just about made of unobtanium and cost far more than .41 Magnum cartridges.
And just to be complete, the .401 Herters is a true .401, and you cannot make cases for it from any other cartridge. Starline made a run of .401 hulls a while back and those and original Herters brass are the only cases I know of for the .401 Herters.