Identity a Pilot’s gunsight.

[RichardSuhkoi]

I have spent some time without identifying this gun sight. I suspect it WW1 as it's marked "100 M.P.H.". I did find that it looks like a Norman sight. It has some other marks visible in the photos.

 

[Greyman]

'100 mph' is an indication of the radius of the ring, not so much the aircraft speeds (though that does factor in).

My hunch is that it's a WWII sight, and that yes it's probably a pilot's backup sight.

The ring radius on the Mk.II reflector sight (Spitfire, Hurricane, Typhoon, ect.) was 100 mph -- while the gunners sights were typically 50 mph.

I know for a fact the Spitfire, Hurricane, and Blenheim rings were stamped '100 mph'.

 

[RichardSuhkoi]

'100 mph' is an indication of the radius of the ring, not so much the aircraft speeds (though that does factor in).

My hunch is that it's a WWII sight, and that yes it's probably a pilot's backup sight.

The ring radius on the Mk.II reflector sight (Spitfire, Hurricane, Typhoon, ect.) was 100 mph -- while the gunners sights were typically 50 mph.

I know for a fact the Spitfire, Hurricane, and Blenheim rings were stamped '100 mph'.

This makes sense. So typically a reflector sight but maybe a ring sight like this as backup? I am surprised I can't find any like it on the internet. I think that here at aircraft net there's bound to be someone who recognizes it. We can say the since its "miles", it is UK, USA, Canada, Australia etc., rather than Japanese or German.

 

[Greyman]

I'd say it's reasonably safe to narrow it down to a British sight, the terminology fits their practice a bit better; '100 m.p.h. sight'. The US did use '100-mile reticle', so I can't be 100% sure.

Plus the construction seems to match other WWII British ring sights I've seen, vs. the US types that most often look more like a circle with a cross.

Obviously a lot of gaps in my info, so I'm eager to see anything more concrete.

 

[RichardSuhkoi]

I'd say it's reasonably safe to narrow it down to a British sight, the terminology fits their practice a bit better; '100 m.p.h. sight'. The US did use '100-mile reticle', so I can't be 100% sure.

Plus the construction seems to match other WWII British ring sights I've seen, vs. the US types that most often look more like a circle with a cross.

Obviously a lot of gaps in my info, so I'm eager to see anything more concrete.

I will try to measure the threads and see if they are Whitworth or SAE. That might help discern USA from UK made.

 

[RichardSuhkoi]

I'd say it's reasonably safe to narrow it down to a British sight, the terminology fits their practice a bit better; '100 m.p.h. sight'. The US did use '100-mile reticle', so I can't be 100% sure.

Plus the construction seems to match other WWII British ring sights I've seen, vs. the US types that most often look more like a circle with a cross.

Obviously a lot of gaps in my info, so I'm eager to see anything more concrete.

The thread on the rod appears to be 3/8-20. So this more implies USA make.

 

[MiTasol]

The thread on the rod appears to be 3/8-20. So this more implies USA make.

American 3/8 fine thread is 24 TPI and course thread is 16 TPI.

3/8 BSF is 3/8 x 20 TPI. The US did not do much anodising but the Brits did so I would say Canadian or British. The part number rules out the Australian Wirraway and Bristol Beaufort - both AU and UK built aircraft. I will check out the part number for the Blenheim and Bolingbroke but it may take a few days. The part number is in the right range for them.

 

[special ed]

3/8 x 24 may be U.S. extra fine thread -- for example 1/4 x 20 is U.S. course, 1/4 x 28 is U.S. fine thread while 1/4 x 32 is U.S. extra fine thread.

 

[MiTasol]

That makes life easy doesn't it.

I am still inclined towards British or Canadian.

You also need to remember that the Brits used similar sights in their gun turrets. This one is on a Blenheim.

 

[RichardSuhkoi]

3/8 x 24 may be U.S. extra fine thread -- for example 1/4 x 20 is U.S. course, 1/4 x 28 is U.S. fine thread while 1/4 x 32 is U.S. extra fine thread.

You are correct. When I compare to BSF (British Standard Fine) my dimension of 0.3745" with 20 TPI matches the 3/8 - 20. So British. That plus the comment on anodized aluminum base mount. Maybe someone will match the part number "73118 2".

 

[RichardSuhkoi]

That makes life easy doesn't it.

I am still inclined towards British or Canadian.

You also need to remember that the Brits used similar sights in their gun turrets. This one is on a Blenheim.

View attachment 811988

The thread it turns out best matches 3/8-20 British Standard Fine with thread outside measuring 0.3745" vs the value on a table for BSF of 0.375". I am hoping that the part number will look familiar "73118 2" found on the anodized aluminum base.

 

[RichardSuhkoi]

Someone wrote earlier of British inclination to use anodized finish. I forgot to mention earlier that the lower mount part is soft grey anodized and the upper, reticle part is dark "sulphuric acid anodized" (hard coat).

 

[MiTasol]

Okay - it is not Blenheim as that is 73289. I would be very surprised if the Bolingbroke one was a different part number.

 

[RichardSuhkoi]

Okay - it is not Blenheim as that is 73289. I would be very surprised if the Bolingbroke one was a different part number.

Those part numbers are very similar. What is the origin of these numbers? Are they from the Bristol company?

 

[MiTasol]

Straight from here. Not my manual and I cannot post it.

 

[RichardSuhkoi]

Straight from here. Not my manual and I cannot post it.
View attachment 812491

So given the similarity of format we can speculate

Straight from here. Not my manual and I cannot post it.
View attachment 812491

Given how similar the part numbers were I spent time searching. Found this photo titled "
Bristol Blenheim Mk.IV, Cockpit Photo by Roly-sisaphus • Photographed at the Imperial War Museum, Duxford Photo ref; SNC10123". I think you have solved the mystery and the gun sight is a Blenheim, maybe superseded by the part listed in your parts list.

 

[Greyman]

As I mentioned previously there are many British pilot ring sights that looked very similar, so personally I wouldn't be 100% firm on the Blenheim just yet.

Though the Bristol part number does seem to be a good lead, if it is a Bristol-specific number.

Beaufort is possible ... unless they're interchangeable (along with Bolingbroke)?

 

[MiTasol]

Definitely not Beaufort - that is

 

[RichardSuhkoi]

As I mentioned previously there are many British pilot ring sights that looked very similar, so personally I wouldn't be 100% firm on the Blenheim just yet.

Though the Bristol part number does seem to be a good lead, if it is a Bristol-specific number.

Beaufort is possible ... unless they're interchangeable (along with Bolingbroke)?

 

[RichardSuhkoi]

Your caution is wise as I found Bolingbroke images and it looks similar. So Beaufort parts list doesn't match, maybe someone has a Bolingbroke parts list ?