You shouldn't require too much extra powder using Pyrodex P because it's about 10% stronger than RS or BP ffg. 90 grains or soshould be enough to equal 100 grains of BP.

Shooting off a bench places the stock in a different position on the shoulder then when shooting offhand sometimes. The same with the eye and cheek position on the stock in relation to the reticle. It's possible that this can cause a noticiable variation on the point of impact on the target downrange.This happens to me at short range oftenenoughwhen I sight in my airguns on precision targets. I usually need to resight shooting offhand afterward. It's very frustrating.
Also, Pyrodex is relatively more sensitive to compacting pressure when the sabot is seated.
Still another factor is barrel temperature. After the first shot the barrel warms up, and now the temperature is even cooler when the first hunting shot will be taken. It's better to fine tune the gun when the outside temp. is closer to the actualtemperature of the barrel during hunting season.
I try not to look at groups so much but at the first shot accuracy out of a cold clean barrel.
It may mean swabbing and waiting 10 minutes between shots so that in the end after sighting in, you're only checking forfirst shot accuracy.
If a rifle is placed further out (or down)on the arm when shouldered, there is a natural tendency for the reticle to shoot to the left of the previous point of aim when the rifle was mounted on the shoulder closer to the neck. At least that's how it works for me because I shoot right handed. I often compensate by aiming to the right of the bullseye, even after re-sighting in off-hand, and I usually alsotry to shoulder the gun closer to myneck/head by pressing my cheek tighter into the stock. Realizing this helps the shooter to learn to shoulder the gun closer to the same placeeach time to keep the reticle lined up closer to the original sighting inpoint-whichshouldlead to shootingmorestraight on.
I hope that you/everyone understands what I'm saying. Scopes are only a sighting tool, and they are not inherently perfect in design. Where once places their eye and cheek when it's sighted in needs to be repeated consistently in order for the scope to maintain it's perfect zero. Move the gun more out on the arm, and it just may shoot left if you are right handed. This doesn't necessarily happen with every scope and every mounting, but the potential for it to happen this way is always there if the scope is low, or the field is narrow or the lens extra large, or the scope lense is not really high end, etc...'Nuff said I hope.

I get what your saying, one thing I am going to try is switching hands, I will do it first with another gun just to see if I can still do it. it has been about a year since I shot left handed. My right shoulder is bad and keeps me from holding the gun right, either way, but nothing can hurt now.

there was one thing I was thinking about today while at work. when doing anything sitting or standing, being comfortable is very importent. I remembered how comfortable I as when I first shot at a 100 yrds and I also remember I had the seat lower then it was the day I shot chitty. I would love to try that load again, but I only have 5 left of the 240 xtp, so I gotta work with the other load I have. I got 30 + of them.

But no matter what, it was not the load, gun, scope, sabots, or bad shoulder it was me that had the bad day.