It should be noted, that the recoil from a heavy slug load is considerable. Some people just can't do it - it's more than they can tolerate.
Chuck Hawks wrote the following in an article on his excellent website about shotgun recoil... These are for shot loads - not slugs...
http://www.chuckhawks.com/12gauge.htm"The principle drawbacks of the 12 gauge shotgun are the size and weight of the typical 12 gauge gun itself, especially the repeaters, and the recoil generated by the big shells. These two factors make the 12 gauge unsuitable for many shooters.
According to the Shotgun Recoil Table the recoil energy of a 1 ounce target load at 1180 fps in a typical 7.5 pound gun is 17.3 ft. lbs., about like the recoil of a .270 rifle. The typical promotional shell with 1 ounce of shot at 1290 fps in the same shotgun hits back with around 20.8 ft. lbs. of recoil energy, about like an average .30-06 rifle. These loads deliver about as much recoil as most shooters can stand on a continuing basis.
A typical high-brass load with 1 1/4 ounces of shot at a MV of 1330 fps fired in a 7.5 pound shotgun is much worse. It belts the shooter with 36.4 ft. lbs. of recoil. This is roughly equivalent to the kick of a .300 Ultra Mag. rifle. Average hunters should strictly limit the number of such loads they fire to avoid developing a flinch.
12 gauge Magnum shells are even worse. A 2 3/4 inch Magnum shell throwing 1 1/2 ounces of shot at 1260 fps from a 7.5 pound shotgun belts the shooter with 45.9 ft. lbs. of recoil, somewhat more than the recoil of a typical .375 H&H Magnum rifle shooting 300 grain factory loads! And the 3 inch Magnum 12 gauge shell firing 1 7/8 ounces of shot at a MV of 1210 fps in that same 7.5 pound shotgun slams the shooter with over 60 ft. lbs. of recoil energy. This is equivalent to the recoil of a .378 Weatherby Magnum rifle, and exceeds the recoil of a typical .458 Winchester Magnum rifle. This is literally recoil in the elephant gun class, and most shooters would be well advised to avoid such loads."
Don't forget, these full bore slugs are .73 caliber and run from 650gr to well over 700 grains in weight. Most of the true monster magnum rifles weigh in @ ten pounds, with very few under 9.5lbs. IF you're going to be using a powerful load in your shotgun, it makes a lot of sense to add as much weight as you wish to that 7-1/2lb shotgun - longer magazine tube and more shells, or a recoil compensator, X-Heavy Barrel, etc.
The 458 Lott in a ten pound rifle delivers recoil just over 70ft/lbs @ 71.1lbs.
The 500 Nitro and 505 Gibbs recoil, measured in 12lb rifles delivers 78.3lbs and 78.8lbs respectively.
Hunting trophy bears is NO sissy game - you can do it more safely with a powerful rifle, but we're talkin' about carrying a VERY heavy big bore rifle that hits with considerable recoil.
GOOD LUCK!