And round shot that is still nice and round. Old-school round shot would be unjacketed lead of pretty dubious hardness(dictated by indifferent purities and the fact that metallurgy was more art that science until quite recently).
I'd be inclined not to authoritatively discount it (muskets and ball-type ammo were obsolete pretty much as soon as rifling hit the scene; but teething issues and sheer logistical inertia kept muskets from being wholly supplanted until well into the 1800s, so god knows what 'home guard' and/or colonial cannon fodder raised on the quick and cheap were using. It isn't uncommon to find multiple-decades-old-and-maybe-modernized-in-part junk hanging around in the nooks and crannies long after it is ostensibly replaced.)
Given how much aircraft cost, and how The Red Baron was pretty serious business, any fire taken from him would presumably have been 7.92x57mm Mauser of some flavor. If the fire was taken from 'standard' german infantry, it should actually have been the same thing(in lower quantities) from Gewehr 98 rifles.