Thanks for the welcome. I've been lurking for quite a while. You and a few other guys here have given me lots of info, for which I'm grateful. I'm using 16 gauge 1/8" nitro cards under the slugs. They fit the 12S4 wads nicely. I got to playing around on Strelok (phone app ballistic calculator, accurate for my rifles, and I recommend it highly) and noticed that with a ballistic coefficient guesstimate of 1.2 and an 1100 fps muzzle velocity a 488 grain slug will still have enough oomph (953 lbf) to take a deer easily at 100 yards, which is what I'm after. They should also be pretty easy on the shoulder. And it starts subsonic, so it won't have that tendency to tumble when it slows past the sound barrier. All this means Kiddo can shoot them, too. I'd like for both of us to be able to use the same slugs. I'll be giving up some performance, but I'm willing to make that tradeoff.
I wish I could find a load for that Accurate #5 for a slug that's over 1 ounce. It ought to be great for an ounce and an eighth slug.