I have a very similar Drilling made by W. Müchler & Söhne, the proofs suggest in 1911 in Zella Mehlis (ZM on barrel). It's 16/65, 16/65, 9,3x72R (D). There's an "RH" inside the action and also stamped on the fore-end loop on the barrel underside. The information I have referrs to this style of Drilling as a Roux breech after a French gunsmith. Calling it a "Treff" is new to me. In German, "Treff" means a hit when you're shooting something.

There's a very out of focus picture of the top of the receiver of your Drilling Cummins which shows what appears to be a golden crown with 7 pearls. Try looking at Wikipedia under heraldry but these symbols in Germany are quite specific and the number of pearls denotes a particular rank. From memory 7 means a Baron. Just to confuse things, one maker used a gold crown as a trademark, but probably not on your combo rifle.

My Drilling is at the gunsmiths as those coil springs ellebr referred to are a bit of a trick. One was broken and the replacement was a little oversize and would catch on the others when it was sprung. So it's now getting a hand made one to fit.