I have a Heym 450-400 3" and had some initial problems in getting the barrels to regulate. The gun was originally regulated at the factory with Hornady factory ammo. Results below:

Factory Hornady 400 gr. loads:

2071 fps in right barrel
2086 in Left barrel

Barrels both grouped well separately but there was about 4 horizontal inches between each group.

Reloading results - all loads used RL 15 and Kynoch wads.

Hornady 400 gr. DGX and 69 gr. RL15
velocity - 2140 fps
very good regulation

North Fork 400 gr. softs and 68 gr. RL 15
velocity - 2150 fps
very good regulation

North Fork 400 gr. FPS and 66.5 gr. RL 15
velocity - 2145 fps
very good regulation

the North Fork softs and FPS both grouped together.

I obviously needed a little more velocity to get the barrels to regulate (for my shooting technique) than the loads the rifle was originally regulated with. I feel I could have also obtained good regulation using H4831 with no wads.