I bought a used Merkel 375 H&H double, no target and no information about what it was regulated with. Last month I shot a buffalo with it in Zimbabwe using Federal ammo with Trophy Bonded Sledgehammer bullets. Merkel USA told me it was probably regulated with that ammo. I picked up the rifle on Oct 17th and left for Africa on the 20th so I had little time to experiment. The Sledgehammers seemed to group OK. 300 grain Nosler Partitions did not. I am about to load up some 300 grain Barnes TSX bullets and 300 grain Barnes solids. Any advice on how to work up an accurate load in a double rifle?

All I've read says -- don't. Stick with what Merkel says (until someone you trust gives you specific directions that have worked for them in their Merkel). The only experimentation cautious old me would do is swapping out bullets in the factory ammo. Still iffy

2 cents

What size buff did you take?

Sent you PM.

Post this down in the Double Rifle area.
First thing is to run some thru a chrono and get the speed.Then play with the loads til it's good.

Although Barnes will tell you they are safe to use in a double rifle, personally I would not use those mono-metal bullets in any double that I owned!