Which rear sight for No5 clone?

[Seaspriter]

Peter,
difference in the Mk1 and No5s sight except the No5 only goes up to 800 yds? But from 0-800 they are exactly the same? That is the marks are in exactly the same place up to 800 yds?

I measured the actual difference between the 200-800 yd gradations on a No. 4 & No.5 Mk1 sight. The difference is significant (it's hard to see on the photo on post # 18. Note: the difference between the two models really has nothing to do with the # of clicks on the screw.):
-- No.4 = .275"
-- No.5. = .250".
-- The distance from the hinge pin to the 200 yd gradation is the same on both models, indicating that from 0-200 yds both guns aim the same.

This means the two sights are significantly different beyond 200 yds. The designers were compensating for the different barrel lengths/different muzzle velocities, etc.

In other words, use a No. 5 sight on the carbine, not a No. 4 sight.