On my Ruger M77 MKII RSM in 375 H&H, I have a factory front sight blade with a height of .330". Using the fixed rear sight, this shoots 1" high at 50 yards and right on at 100 yards.

I want to replace the front sight blade with a NECG white bead made for the Ruger rifle ( http://www.newenglandcustomgun.com ). The NECG bead itself has a larger diameter at 3/32". I don't know the diameter of the factory brass bead. The NECG's are available in heights of .330", .350", .375", .415" & .435".

To stay the same, or acheive dead on at 50 yards with the fixed blade and dead on at 100 yards with the first flip up blade, which size do I order?

Stay with the .330 and you will still be 1" high at 50, and perhaps 1.5 at the most due to the larger bead, you can always fine tune it by filing the rear down a hair....

If you get a higher bead then you will be shooting quite low...

As always, thanks Ray.

SBT

Stay with the same overall height on the front blade. The size of the bead doesn't matter. The overall height is still the same. You might have to deepen the vee on the 100 yard sight leaf to accommodate the larger bead, but don't lower the height.

As for the 50 yard height, you will need to lower the overall height if you want to have it shoot dead on. Go slow, depending on how far apart your sights are, 3 or 4 thousandths could move the bullet impact a half inch or more at 50 yards.

After you have the height of the 50 yard fixed blade where you want it, then alter the vee for the larger front bead.

The Brownell's catalog has a chart on iron sight measurements.