Kombi 1976,
I have a few big bores, a 500 Jeffery on an M17, a 450 Ackley on an M17, a 450 NE 3.25" on a Ruger #1 that weighs 8 lbs and various others.
The few things I try to focus on are -
The basic sighting and squeezing the trigger are identical for every calibre, its only after the firing pin falls that things change. What I'm trying to say is don't be scared of a big bore, if you tense up the muscles in your shoulder area, its going to hurt even more. Get a good grip on the rifle without trying to squeeze the oil out of the stock, you need to hang on to them, but a death grip will make things worse as well. I try to keep my forearm hand out as far as is comfortable, the stance you see silhouette shooters using will not work with a big gun. Pull the butt back into your shoulder fairly tightly. When the rifle recoils, go with it, but don't let it take you off balance, let it recoil but control it as well, you will need to learn this to accurately get a quick second shot away. I lean into the rifle a bit, but don't exagerate it, as when the rifle recoils, the motion will need to get you upright first then move you backwards. It's the getting upright bit that can hurt you.
Enjoy your rifles.
DC