@mark-hunter, some really great advice here for you.
Based on practice (not hunted with it) with the 450-400 I owned for 8 years; my practice (300 rounds) was to learn the
manual of arms for a double rifle.
My experiences are:
- Get a SXS Double 12 gauge with double triggers. Shoot and handle it a lot. Front trigger first for me.
- Have dummy rounds made (at least6) that equal the weight of factory ammo, with Delrin primer inserts.
Snap caps I only used to release the sear when storing the rifle. Same weight cartridges for muscle memory to train my hands to handle this specific weight.
1. Practice (with the rifle in a safe direction) with the dummy rounds to mount and shoot quickly. Pull both triggers in sequence, front then rear every time with proper dummy loads that protect the firing pin with a proper primer insert.
I mounted a cape buffalo picture on the wall in my garage, and used the dummy rounds to pull the triggers, extract, and reload quickly. On sticks and off hand. When I found the right cartridge belt, it became easier. I reloaded with weak hand, held the opened double with my strong hand.
It's a personal choice, strong hand vs. weak hand for reloads. As you stated you reload your break open shotguns with weak hand, no need to change
2. Shooting Stance: I opt for the African hunter's preference. I learned this by reading Pierre van der Walts
African dangerous Cartridges. Square up to the target, left foot forward slightly, and ' give shoulder'. Meaning your shooting shoulder
(I'm right-handed), is a bit forward.
Roll with the recoil, don't try to stop it.
The real key is a
consistent firm grip with the rifle tucked firmly in your shoulder, and taking the recoil, not trying to stop it with a death grip. This helps with consistent accuracy.
3. Range Practice: Only shoot 8 to 10 rounds in a string (very dependent on caliber). Once I have determined POA matches POI, then I only shoot reactive targets for instant feedback (clay pigeons, half gallon milk jugs, etc.)
Good luck and send us pictures.