best replacement slugs would be the Lyman sabot shotgun slugs, 525 grains in 12 gauge and 350 grains in 20 gauge. A 350 grain projectile with a velocity of 1400 fps smacks a deer or hog with 1523 ft lbs of kinetic energy per square inch at the point of impact -- harder than a 44 magnum. In short, it delivers serious smackdown power.
Also, the Lyman sabot shotgun slugs can be loaded into standard shotshell hulls and fold crimped. A 25-pack of the Lyman loads would be somewhere in the neighborhood of $7.50 as opposed to 10.00 or so for 5 rounds.
I load Lyman 525 grain slugs into a Remmy Gun Club hull with a Win 209 primer, WAA12 wad, and 25 grains of Herco. It tears the insides out of Florida's demon swampwalkers.
Hope this helps.
ST762