I've tried some online calculators and they're giving 270-300 ft-lbs, which is still brutally high. 8200 ft-lbs of energy might be much though. Comparing 8 bores what I've read shows 5000 to 6000 ft-lbs. I don't know of any chrono recordings for a 4 bore express round.

So for best case, assuming a svelte 1600 grain projectile and 6000-7000 ft-lbs KE with 20 lbs rifle, that works out to 190 to 227 ft-lbs recoil. Still higher than any Nitro Express round.