Well, to answer your question, prob'ly 30 or so grains of Unique over a standard 209 to begin with and then develop from there. The main question, though, concerned the mechanics of paper patching a RB.
As an old muzzleloader shooter, my first thought would be to use a cloth patch...but of course that wouldn't work.
So my second thought is to mold wet paper closely around each ball (and maybe tie it in place), let the paper dry thoroughly while on the ball, trim it to fit also while still attached to the ball (that is, remove the paper "sprue"), and then maybe smear the outside of the paper patch with a little tallow or other ML paste lubricant. Load the patched ball into its shell with the trimmed end of the patch either straight up or straight down.
(Straight up, and the patch will come off of the ball while in flight. Straight down, and the patch will probably stay in place on the ball.)
According to Beartooth's round ball weight calculator, using wheel weights as the alloy will produce a 477 grain ball.
On your second question, I can only assume you're asking why I want to patch it. To improve the bore ride.
Once apon a time, I shot a lot of round ball loads out of a Remingtion 1100 with a CYLINDER BORE.. I used a recipe by Sam Fadala that used Federal hulls and wads with the petals trimmed off. Ball was cast out of wheel weight metal .001 under bore. They shot like a house afire with no leading. It was a long time ago but, I think I used the standard Federal crimp.
Have you loaded any of these yet? Why do you think you need to paper patch the round ball? You should not have any leading problems if you cast the ball .001 under bore diameter and use a CYLINDER BORE.
Well, to start with, I CAN'T cast the ball .001 under bore. That would require a custom built mold and I don't have that kind of money to play with. The only ball mold that's remotely close that I can afford is a Lee .690 RB mold.
The bore, as I mentioned, is .720 . That's 15K on one side. That's a lot of slop that's not going to be user friendly to the accuracy of the ball or the bore of the shooter.
I didn't say I HAD to P/P the ball. I suggested it as a method and asked for comments. I apologize. I truly didn't mean to stir anything up.
...So you want to use paper that's 0.015" thick?
(0.720 - 0.690 = 0.030, and 0.030 ÷ 2 = 0.015)
Have I got that right?
What sort of paper do you propose to use? Is it readily available thick enough?
If I remember correctly, ol'-timey paper-patched ogive-point and flat-point lead bullets required one or two turns of high-quality linen (not wood-pulp) paper.
Why not just use a plastic shot-cup-style petal wad, with a round ball of a size to fit the inside of the shot cup? If the wad's petals were too long, it'd be pretty easy to trim them down. Then vary the thickness of the wad column to make the necessary length to fill the shell to the crimp.
If it's for, um, anti-personnel use, have you considered a buck-and-ball load? There's at least one of these available commercially.
I've loaded a lot of 12 ga. for trap and skeet, as well as some field loads for upland game. A lot of the caveats I've encountered in loading for shotgun say "Use exactly as shown - don't interpolate loads." Shotshells work at such a low pressure (compared to most modern metallic cartridges) that you can get yourself in trouble before you see pressure signs like you would if you were developing a load for, say, a .30/06.
(Actually, I think they mean don't extrapolate loads - going beyond established limits. If two otherwise identical loads use 16 and 18 grains respectively of the same powder, it's safe to conclude that 17 is fine. That's interpolation. Pouring in 19 grains because the listed pressure for 18 is moderate might not be such a good idea.)
Now, as for loading a big round ball . . . I'm curious, what source data are you working from, or do you have some pressure measuring gear yourself? (Personally, I'd be reluctant to strike off entirely on my own for something like this . . . )
A few years ago I had a friend of mine load some 12 ga buck & ball loads for me. He settled on a shot cup for steel shot, a .690"round ball (bought off the shelf from Dixie Gun works) and 3 OO buck on top. They grouped into 8-9" at 75 yards for both the RB and the buxkshot. He had the tools to do a roll crimp with a plastic overshot disc. No idea on loading data, but recoil was not excessive.