Quote Originally Posted by Mk VII View Post
If that's the case then I can't see the point of placing the mark (which screams "segregate me, I am different") on the moveable arm, which only carries the vernier plate. It should be on the base, on which are engraved the (supposedly different) range marks.
Good point - and I dont know !
maybe the small 'plate' that fixes to the elevation arm has a different calibration (but then why not just engrave the 'plate' with 7.62 ?)

I have used a 5C, a 4651A and an AJP 4/47 on my No4 with no measurable differences.

I recently purchased a Long Branch No4 7.62 'target' rifle that had a 4651A sight (with a correct Sterling mag and PH tunnel front sight it looked 'original').
This helped give credence to the story that 4651A = 7.62.