The PLAIN Hornady xtp is a 44 cal. bullet I think they use use a green plastic sabot to fit the 50 cal. bore and do have a greater ballistic coefficient
The xtp mag are .451 diameter and have a heavy core jacket compared to the regular XTP but the have a little less ballistic coefficient,which I could never understand.
I have found in my t/c the xtp mag are hard to load after the first shot in my sidelocks.I also use the hornady xtp mag in my 54 cal. thunderhawk .451 bullet drop into a 54 cal. harvester sabot that shoot oustanding