WW1 'Periscope Prism company' sniper scope???

[Surpmil]

There you are: "RTFRM" (Reference Material!) It's not like I don't have a well-thumbed copy.

So what we have here is a very early PPCo. that someone has added an objective to later? We do see hand-engraved range markings on the earlier scopes generally IIRC, so that would fit here, despite the nicely pantographed but superfluous "Hundreds of Yards". A helpful hint for novices? (H-P again: "Where did you get that rifle? It was issued to me as Trench Stores sir!")

When did they stop sending the rifles to Bisley to be shot in before the range markings were engraved?

Agree re: order dates too; often who knows how much later than actual deliveries. A result of Whitehall/Horse Guards bureaucratic methods?

If the objective was an original type we might have expected an example to be in that well known inventory you refer to I expect.