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As found through the Hodgdon tool, I was pursuing 18.8gn of Clays. This should have resulted in 5200psi, 1200fps with a 7/8oz load and the CD-4100-12 wad. The bushing used was a #33, which MEC's chart states yields 18.6gn of Clays. I measured this 10 times before I started reloading, and they were consistently within .3gn of the target.

I disassembled five shells last night, and found the following:
7/8oz charge bar, #8 = .875oz - .888oz
19.2gn - 19.7gn

I suppose the powder settled a good bit, because the bushing tested right at the beginning.

If I match up what I discovered by dissecting, then I have something very close to the next load up in power with these same components, which would be 6100psi, and 1250fps.

Is 6100psi and 1250fps considered too stout for damascus/twist barreled guns in good sound condition? I would think it is not, even if it's not pleasant to shoot.

Most try to shoot 5000 psi as a arbitrary "magic" number. And it's more for stock preservation than fear of Damascus failure. I'd drop your powder a little. In fact I try for 1100-1150 fps on clay targets. Very soft shooting loads and plenty to break clays or even harvest most game.

My standard load is 5200 psi, 1100 fps with an ounce of shot using discontinued PB powder. Very comfortable load to shoot and fits in hulls without having to add extra cards to fill up space. Pity they stopped making PB, it was a versatile powder for 12 & 20.

Thanks. I've dealt with the stocks to keep the strong. Wasn't too worried about the barrels, but thought I'd ask nonetheless.

Dropping the powder is not an issue? Maybe to 17.8gn or so?

For several seasons I shot an 8K "LUP" load through a Birmingham black powder proofed J P Clabrough Damascus barreled double with no problems whatsoever. Load was with the then New "HyScore", not 700X & used 1 oz of shot @ about 1150 FPS.

Nota Bene (Note Well) that it is shot payload & velocity which affect the stock, PSI has virtually nothing at all to do with Stock damage. PSI essentially affects only the "Max" chamber pressure, which affects only the chamber area of the barrels.

Any barrel beech which will not handle 7K-8K psi needs to be hung on the wall or at least confined to light loads of Black Powder only.

Operating the loading press will condense the powder in the hopper. Check weights should be taken while the loader is in normal operation.

The stock heads of what I shoot usually have had the old oil leeched out, the stocks refinished, and the inletting impregnated with glue. I'm not too worried about the stocks.

My primary concern was keeping pressures to within a reasonable level for the barrels. Feedback here seems to indicate that the pressures I have are fine.

The task now is to determine what of the materials I have, in what measures, will give me a shell that I can shoot several rounds with and not hurt the gun or my shoulder. Thought I had a good candidate, but settling powders, and my newness to the activity have proved there is more to do and learn.

The Hodgdon site lists 19.8 grains Clays in a STS case with Win. 209 primer and CB-4100-12 wad at 6100 psi and 1,250 fps
http://www.hodgdonreloading.com/data/shotgun

Yes Sir, that�s what has ended up being loaded. #33 bushing was used, which when the powder settled threw more than the chart.

Is it correct to think that keeping all other variables the same, but lowering the powder, will both reduce pressure and velocity?

What is the outcome in these areas if the payload is reduced?

I think, for clay targets, if your components can give you a load that is in the 1100 to under 1150fps range, you will feel the difference. Before you do anything else, maybe try your current bushing again, and confirm on your scale, that it will drop the heavier powder charge, while you cycle the press as if you're loading. There should be multiple pulls on the handle with various functions for every drop.

If you can recreate and confirm the heavier drop, then go lighter. There were ideas earlier about how to reduce the inner diameter of your bushing, I prefer the tape idea figuring if it ever comes lose it should be easy to tell that sometime isn't right. Maybe, you can figure this out before you purchase anything else.

If you come up with something you like, maybe you can use up the heavier loads a box or two at a time in the beginning of a session before the recoil gets to you. If your cheek is okay with the recoil, maybe some pad on the gun or your shooting shirt would, not just for the heavies, make your lighter loads more enjoyable for your situation. Best of luck with it.