No1 sight and rated for Mk7 amo?

Remember those loverly rear sights on the No1 Enfields with all the different adjustments? I've noticed that some have a V shaped notch and others a U shape. Am I correct in thinking the U shape is like the No1Mk3 U notch and therefore is the later made version? And would that also mean that the U shaped notch are rated for Mk7 ammo, and the V shape for the earlier ammo, MkV1? Or am I reading too much into it?

That's a good question RJW........... seen plenty but never thought about it

LoC Paragraph 13853, dated 26 Jan 1907 covers it. The 'U' notch came about at the same time as the changeover to the straight post from the barleycorn front sight.

Edit to add...it was part of the spec for the new MkIII SMLE, rather than having anything to do with the Mk VII ammo.