Andy, I believe the sight set that came with your gun has four plain black blades for 50-100-150-200 yards. I am not sure I read your question correctly, but to get to the point, if I were in your shoes, I would put the 50-yard blade (the tallest one) in the gun and shoot the group (3 rounds only, since you want to be conservative with your ammo) using the normal hold you have established for the gun and 240-grain ammo. I do not think you will see "a lot" of difference with the 210-grain shells at 50-yards. It is just a guess but I would expect maybe 2-3 inches.

If you cannot use a bigger sheet of paper behind the one you plan to use, for some reason ( ? ), you could always cover existing holes with tape or pasters.

As to the mathematics involved in making a calculation, I am sure it can be done, but it is way beyond the means of most of us here. It would certainly vary with the strength of your grip on the weapon, which of course is an individual thing. A WAG might end up being as good as the actual calculation.

"Take the field" and forget the mathematics on this one.