Too stupid to get the link at the moment but GI has a listed 410 under "Army Navy Shotguns" with what looks like a new label on case, no pic of AN on gun and PV proofs?

I have never seen an Army & Navy that was not UK built, could have happened but I do not think so. Looks "spurious" to me.

https://www.gunsinternational.com/g...top-english-quality.cfm?gun_id=101720578


Price: $9,150.00

Shotgun Gauge: .410 Gauge

https://www.shotguns.se/html/belgium.html

If the barrel proof is O then 1936

Did AN ever do anything other than British guns?

They certainly offered imported guns. This 1937-8 catalogue also shows Mauser, Mannlicher-Schoenauer , Remington and Winchester rifles.

The entry for .410 doubles does not specify origins, although the single barrel Ward’s patent gun just below is shown as (British made).

They did not make guns themselves but those made for them in the Birmingham trade were simply branded Army and Navy whereas this .410 is marked as Shot and Regulated for them.

No doubt sold and possibly cased by them, but not an English gun. Also made as a 2 1/2 inch (65mm) gun and apparently never re-proved for 3inch cartridges.

I agree the lettre annale is 'o' for 1936
The gun was proved with 65 mm = 2 1/2" chambers
There are meaningful marks forward of the ejectors that the seller did not include; possibly a maker's mark