I'm cautious firing truly unknown rifles. Something made in 1888 is 130 years old. I know enough about those particular old Mausers to be concerned for their mechanical lockup after GOK how many 'I read somewhere' researchers slash experimenters fired unknown strengths and numbers of prewar, WW1, interwar period, WW2 and postwar commercial ammo. They were already modified in the service to accommodate two available types of ammunition. IMHO, there is just no way to know what may or may not have been done to this rifle in its lifetime.
Would I fire WW2 8mm in a G43? Nope. Those rifles are a weak design that was put into production about a year too quickly. Those rifles get the light Privi 130-gr ball. But I would fire that same 8mm in just about any M98.
Would I fire WW2 .303 ball in a No.4? Absolutely. Do it all the time. Because I have a better sense of the manufacturing quality control on the rifles and the ammo.
The original poster asked what he's got. So I answered.