I took an H&R heavy slug gun and ordered some three inch 12 ga hulls from RCC. That was four years ago. I had a custom .730 mould made that drops a 750 grain bullet. I've been shooting 120-150 grains of 2F in it The recoil is brutal and I'm no softy. I dress out at 6'3" and 350 lbs and am not recoil shy but dang guys, this thing is a womper. Now add the smoke and the dirt and I'm not as in love with the gun as I once was. So, the thought dawned on me, what about going smokeless? The trouble is I have no idea where to start. I have maybe 10 lbs or AA5744, a boat load of Universal, Blue Dot and a few other powders. Where can I go to get some starting load data>?

I used data from a very old shotgun reloading book. I'm at work at the moment but I'll look it up and post my load. See http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=342043#Post342043

I got my load from the Lyman shotshell handbook 3rd edition.

You didn't say what you use the gun for, but any smokeless load that delivers similar velocities to your BP load is going to hurt even more. At 5 1/4 lbs (listed weight of the rifle) any BP or smokeless with that heavy slug is going to have some serious recoil. To reduce recoil, you could add weight to the inside of the butt stock, use one of the mercury recoil reducers, add a slip on recoil pad over the existing recoil pad or reduce the powder charge.

I use a modern 10g with 1 1/2 of shot and 120 grains of 2F for cowboy shooting, but it weighs about 12 1/2 pounds so it doesn't hurt.

If its the heavy/bull bbl version, it will weigh around 9 lb...I have one in 20 bore.It must weigh all of that with the scope.
Had a ball mould made.
It was very mild to shoot, but I don't know what pressure.
I just used a very mild 1oz 20 bore load for the -7/8th oz ball,petals cut off the wad, some home made felt wads,then the 20 bore ball pess fit into a remmy case, nocrimp, sealed with blob of crisco.
I'll have to end some to Tom Ambrust
good luck
franc

Being a smart, selected and astute Madison Fellow, why would you shoot close to 2 ounce slugs out of a shotgun??

You do know you can shoot regular 2 3/4" slug loads out of this gun?

http://www.buckandslug.webspace.virginmedia.com/slugdata/12f705data.html

http://www.ballisticproducts.com/Slug-Loading-Manual-3rd-edition/productinfo/00MSLUG/

Actually a smokeless load delivering the same velocity will not give a higher calculated free recoil. No smokeless load giving the same velocity will require 120-150 grs. of powder. The weight of the powder charge is a factor in recoil calculation. Smokeless may well give a sharper recoil but the ft. lbs. will not be the same.