That looks like a super wad for smokeless RB loads, David.

George - from my perspective - the 1oz. Foster lags behind the RB in weight to diameter ratio and thus is too light for it's diameter, while the 1 1/4" Federal slug comes out the same as a .715" RB in weight, making it the best of the Fosters. Thus, the 1 1/4oz. slug would be ok - however. Trouble is, the Fosters are pure lead or very nearly pure lead and squash up upon impact with hard objects, turning into more like disks. Upon ignition, they shorten/slug up/obturate to fill the bore. In expending to fill the bore, they shorten. If the gun is a norminal 12 bore, ie: .729" or .730", the slug doesn't have to expand much to fill it, but any expansion takes away from it's aerodynamic advantage, if any, squashes/flattens the 'vanes' and distorts the slug's side, sometimes causing slumping to one side or the other. This changes the integrity, trueness of the bullet's base, causing problems upon departure with the muzzle. I am possitive this is why Fosters give unaccounted flyers - sometimes wayyy out in left field. I don't trust that I won't get a flyer when shooting at game. I want to be able to count on the accuracy of my gun, every time I pull that trigger.

A gun's bore/groove diameter that is the same size as the Foster will reduce slugging or compression to a minimum and 'probably' give the best accuracy. Their failure on heavy game and soft lead fouling then becomes their primary disadvantage, imho, of course.