8Bore - I too am primarily a collector, due to the repressive firearms laws over here in the UK but try to shoot on a range when possible

If you want to try a load with less recoil one option is to use Round Ball. I do this with almost all of my Sniders with the standard load of 70 grains
This is less than 3 drams (82 grains) and the lighter ball and smaller contact area will keep recoil to a minimum for a starting load
I also use a recoil pad with heavier loads

Be aware that this load may not regulate in your Double, it being regulated for 3 drams and conical bullet

I use a .600 RB an all my Sniders but that will not go anywhere near my Williams & Powell double chambers

As you have a taper bore (like many Sniders) possibly slug the bore from the breech, just tapping it in enough to clear the cone. Roll the slug in the caliper jaws if there is an odd number grooves (is usual)
The RB especially in pure lead will not push up pressures much

For the W&P I initially put the loaded round in the FL resizing die (without the decapper!) and just give it a gentle squeeze,
enough to seat and grip the ball and stop it moving forward with the recoil from the other barrel. Shoot both barrels regularly , not use one barrel leaving the loaded round in the other
As I have several Sniders I keep the cases for the double separate from all others and they do not require resizing

Just a thought to give you another option if you wish

Good luck as always

TH44