older 8mm mauser ammo was .318 and barrels matched... later a .323 was adopted and many mausers have a marking on the barrel to differentiate bore diameters so soldiers wouldn't use the wrong ammo in them.
my guess is that his g88 was a 318 bore and that yours is a 323 bore. the ammo you tried in his might have been slightly underbore and better suited to his barrel.
ignore my complete lack of capitalization. I still have no problem correcting your grammar.
I never said half the stuff people said I did-Albert Einstein
You can't believe everything you read on the internet-Benjamin Franklin