40 mm Bofors AA guns made in GB and US

[Richard Suggitt]

I would like to take a moment to introduce myself and tell you why I'm here....
I am a volunteer with The Shuttleworth Collection (in effect, an aircraft museum, but I should not really call it a museum. Just about all the aircraft are regularly flown and the vehciles we have are regualrly driven and displayed).

The collection has a Bofors 40mm AA gun, which we display on flying days and invite the public to sit on and operate (which is a lot of fun if the aircraft are flying at the time).

We need to learn more about this gun, and do some maintenance on it during the winter.

This is the gun in it's weekday static display position in one of the hangars....

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[Richard Suggitt]

There are a few things we are having trouble with. Firstly, this is the barrel elevation mechanism.

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We have a slight oil leak from the bottom of the vertical column. We are not sure if this mecahism is supposed to run in an oil bath or actually be full of grease. It's possible that over time some of the grease has liquified, or that someone put oil in it and then topped off with grease. If anyone has some information about how this is supposed to be lubricated I'll be very happy to receive it.

[Richard Suggitt]

The next problem is the 'accumulator' springs. These are in the two horizontal tubes under the barrel and contain springs that compensate for the weight of the barrel. In our gun the springs seem to be very weak and let the barrel fall under its own weight. We assume that the springs need to be removes and re-tempered. Has anyone done that or know anything about it ?

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[Richard Suggitt]

Then there's the sighting corrector. We've worked out what most of the dials do (though we're puzzled as to why it turns around as the gun itself turns). However, we're not sure of the purpose of the white metal horizontal dial that is situated at the bottom. It has markings of 0 to 40 (which somewhat mirrors the vertical azimuth scale that's in front of the operator and goes from 0 to 400). Any ideas anyone ?

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[Richard Suggitt]

Nor have we worked out what these two controls are. Each knob can turn three times, each has two opposing scales. It feels as if it's some sort of coarse setting for the sights, but we have not been able to set them in such a way that the sights exactly match the barrel.

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Just for completeness, this is a closeup of the actual sights. We know that the items that look like boxes are the night sights.

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As I said earlier, any information will be gratefully received ! Many thanks in anticipation !!

[notenoughtoys]

Richard I have found my copy of a small Finnish manual I have and it is listing that lower dial as a "pysyttimen 7". Google translate is not finding this word so hopefully someone will chime in and translate. I believe the two upper knobs are for zeroing the sights and may not line up exactly with the barrel due to minimum range and bullet drop ??
If you can post your email I will scan in all relevant pages in my manual and send them to you in a zipped file.

[Richard Suggitt]

Originally Posted by notenoughtoys

Richard I have found my copy of a small Finnish manual I have and it is listing that lower dial as a "pysyttimen 7". Google translate is not finding this word so hopefully someone will chime in and translate. I believe the two upper knobs are for zeroing the sights and may not line up exactly with the barrel due to minimum range and bullet drop ??
If you can post your email I will scan in all relevant pages in my manual and send them to you in a zipped file.

Many thanks for responding ! I'll pm you my address.

[Richard Suggitt]

Originally Posted by notenoughtoys

Richard I have found my copy of a small Finnish manual I have and it is listing that lower dial as a "pysyttimen 7". Google translate is not finding this word so hopefully someone will chime in and translate. I believe the two upper knobs are for zeroing the sights and may not line up exactly with the barrel due to minimum range and bullet drop ??
If you can post your email I will scan in all relevant pages in my manual and send them to you in a zipped file.

Like you I cant find a translator that will give me the English for "pysyttimen ", but I've googled the word and it crops up in a number of different contexts.... I suspect it could mean something like 'illustration', 'assembly', 'part number' or suchlike.

[Richard Suggitt]

Originally Posted by Richard Suggitt

Just for completeness, this is a closeup of the actual sights. We know that the items that look like boxes are the night sights.
Attachment 102017

Slight picky update.... the sights are not specifically night sights. They seem to have been made by a company called AGA-BALTIC and are more properly called Reflector Sights or Reflex Sights. They can be used at night but also have drop-down filters so they can be used in the daytime.

[notenoughtoys]

Scans sent - if you need any other details please let me know. Still looking for one more reference book (no luck yet) so I will email you if it ever shows up !