Re: seating into the lands?
I am not sure how one could seat them into the riflings 10, 15, or 20, it seems like to me that once the bullet makes contact with the rifling then that would be it. You might be able to go farther if you had very tight neck grip thus not allowing the bullet to be push down into the case.
But as far as your powder charge that you are asking about, it would depend as to the charge you are using now. We have no idea if you are at "full" throtle or what.
If you are at "max" now, then I would reduce my charge a 1/2 gr. But only go no more than .010's farther out and try it. I do not have a lot of experiance in using B.T. bullets, but the one's that I have used have mostly shot the best @ .050's off...but as you know every rifle is different.