WW1 'Periscope Prism company' sniper scope???

[lmg15]

Many thanks Roger - a picture tells a thousand words - I should use more of the former and less of the latter! Apologies everyone, but I did warn that it would get arcane. I will post some more photos to illustrate specific points when I can wrangle the technology, but I think you have nailed all of the main points I was trying to make.

Brilliant specimens there. The scope with the M 30xxx series number is interesting. The number would equate to an LSA rifle made mid-ish 1915, or a BSA made in 1940. More likely the former, but may indicate a rifle drawn from stores if built up into an overbore sometime in late 1917 or 1918? ATB, D.