The information I have is the Nagant rim is .050 while the 25-20 rim is .065 so there is a difference of .015. That is enough to affect the headspace. Can not be that good for case life, however I do not know how much it will affect either. There is at least one company online selling the 7.62 brass from PPU converted to .25-20 Win. They do not address the issues of the rim, and as yet I have not had a reply to my email to them. The folks at Buffalo Arms said they sell the Nagant brass to people who do the conversion as well since .25-20 brass is very difficult to obtain and almost that bad with .32-20 or .218 Bee. So far I have not been able to find any information on the issues with the thickness of the rim or the smaller diameter regarding case life, headspace, ignition, extraction, or separation of the head. I did just receive some new PPU brass so I will be finding out in the next few days from my own testing. All of the loads will be cast 87 grain linotype and light charges of smokeless powder and some 15 gr 3F Swiss.