Anyone care to guess the age of ?

I'm trying to match, age wise, the approximate aperture sight to my fultons no1mk3. I'm considering BSA G's, AGP, etc, something with a bit more character than the usual ph5a.
Its says BSA Co on the right side of the wrist, no other marks on the wrist or receiver left or right side, the knox has two sets of numbers on the right, top is 505c in an enfield looking font, and below it is 9651 in a fractionally smaller and italicized font.
Any guesses as to the decade?

Unrelated Q; if one had to frame a golden age of target shooting with military rifles, what era would it be? I automatically think Edwardian but...

1930s commercial BSA.

That's what I'd say too. Called in by the government in 1939 and renumbered. Quite why the rifles were all renumbered with a what they called a 'census number' is a bit of a mystery because there was already a serial number. Someone from the Ordnance world told me many many years ago that the reason was because the commercial 'serial' number wasn't an Ordnance 'registered number'. The difference being that an Ordnance 'registered number' was never (?) duplicated whereas a commercial serial number was often duplicated, depending on the whim of the customer.

Not duplicated in THEORY, but certainly duplicated in PRACTICE, albeit by mistake!

I think that the right sight for it would be the BSA commercial type 9 (1912) type........ and guess what I have just been enquiring about?

In addition to the 9G and 5A, the 1936 Parker-Hale catalog lists the "Plus Five". It's a neat looking folding sight - kind of like a modernized version of the No.9 series. I want one.

http://www.rifleman.org.uk/PH_Service_sights_Main.htm

The Parker Plus Five is the "beefier" of the folding sights and I believe the last of it's type.
BSA No9's appear to me more prolific than the aformentioned and the 5a is probably the most common seen in the UK on the smelly.

I've got one of those 'Plus Five' ones here. One would have to sand the forend down if it overhangs the metal much (as many wartime ones do).
The additional number seems to be a thing on those pre-1914 commercial sales ones. Might be connected with the SALE PERMIT marking which they had at the time.

What a nice surprise, of the two favorite sights I have here one is actually a plus 5. Based on its looks I'd guessed it as being a much earlier item.
The other sight I have here that isn't mentioned except in general terms in the Rifleman site is a TZ AJP model L. The nomenclature is well explained there but with the L designation its outside what they describe, so its a bit of a mystery.
. Apparently on TZ sights the last digits are the year of introduction and the ones preceding the slash are the model its designed for.