It is certainly a sporting rifle built on a M88 "Commission Rifle" action. Haenel made a lot of these, but so did V.C.Schilling and other Suhl gunmakers. The pre-1912 service load marking 2.67 gramm GewehrBlättchenPulver = 41 gr (military) rifle flake powder (smokeless) points to the 8x57I as the original chambering, but the rifle may have been rechambered to 8x60I in the 1920s, due to lack of the then forbidden 8x57 ammo. If so, there should be a crown/R repair proofmark under the barrel. Take the rifle apart and post a photo of all the marks on the underside of the barrel. That 7.5x60 may come from a common misunderstanding of the old German proofmarks: The German proofhouses did neither mark the cartridge designation, nor the bullet or groove diameter, but the narrowest land diameter of the barrel.