this is kind of like comparing oranges to tangerines
8mm mauser is slightly more powerful at close range, and it has a bigger bore diameter and bullet an 8mm is a .323 190 grain (typically, turk ammo is different)bullet vs. the russian with a .311 147 grain (typically) but the 7.62x54 is a more ballistically efficient round( boa tailed with high ballistic coeficient) and will pass the 8mm at ranges past about 200 yards. the difference in power is so small that it can be said it is insignificant. really it is less a comparison of ammunition and more a comparison of guns, do you like mausers or nagant's better. if you go with a nagant, buy a finnish m-39, even with the cheap (900 rounds for $80) ammo it can keep a pop can bouncing at 100 yards with open sights. as for looks the mauser wins hands down. either way if you buy a specimin in good condition you will forever be happy with your purchace. btw the turkish 8mm ammo is interesting looking when pulled, i'de say it's loaded with about a 140 grain bullet, as it is as short as possable once it goes past the neck of the case.