Well, I know it's not my conjecture, I'll find the source. However, I well know how conjecture and gross generalization gets wound into the literature. Somebody finds one Enfield with the sight knocked off, and decides they all had the sights knocked off. Nobody seems immune to it. In Pfanz' book on the third day at Gettysburg, he talks about how the Yankees at the stone wall had extra .69s "left behind by Wright's Georgians" the evening before. As far as my research indicates, Wright's Brigade had no .69s, and the 48th GVIR, the unit most likely to have left weapons up there since they had such heavy casualties, had Enfields. So, it could be some historian's conjecture on this issue as well.
I'd never run accross the practice of charging men for the cartridges. Was that an AOT practice, or can you document it as a PACS practice?