Not an expert so listen to more opnionsthan mine, but the original will float if you carefully place it on the surface of a glass of water and then sink if tapped, it will have a dull sound if dropped on a china plate, the repro wont. Best way to tell the difference (which is what I did to check mine) is to buy a known "repro" sabre (cue flames :evil: ) the difference will be more obvious. When your certain you have an original, throw the repo into a hot furnace!
Whatever you do, dont get them mixed up
mark the repro clearly!! Hope that helps?