+1 on the Federal loads. I've not used any fillers either.
Heym regulates their rifles with Wolgang Romey ammo. If memory serves me, they use Woodleighs.
As for shooting, stand up and rest your hand on bags on some sort of rest. I built a double rifle rest that looks like a very tall bench.
Another aspect is to make sure you're not canting the gun. This can really cause some odd problems, particularly if one barrel is shooting a bit higher than another.
