I don't think the winchester wads with "AA" anywhere in the product code work well in UEE cases such as the Cheddite. You might want to try the REX wad or the wad I use, the Super Spark" These seal better in the Cheddite and Fiocchi hulls.

I like Daryl's idea of trying a lighter RB. Certainly worth trying, but I understand your thought process.

Boy, I would roll crimp. You want durable ammunition. The BW is just so tender. I recall you mentioning you were worried about roll crimping. Back her off a 10% or so and give it a try. There is no problem I know of, I'm confident there would be some flap out there that I would have picked up if there was. Roll 'em. You may move impact of the individual barrels by adjusting the wad column too.

I'm not aware of anyone measuring case head expansion to determine shotshell pressure. Please be carefull. Maybe someone else can provide more info (or confirm my thoughts).