So, here are first results with the 1966 Merkel Bockbüchsflinte:

I started with a 20 box of GECO 165 grain 7x57R.
Sighted in the rifle, noted that yes, she shoots well.
Till now I used this ammo to shoot two roedeer, a doe and a fawn.
All fine.

Now into reloading, here is a target shot at 100m with 140 grain Nosler Partitions,
actually these are leftovers from my fathers reloading bench, purchased sometimes in the 1970s

That historic combination works nicely.
fuhrmann