Japanese pumper?

[Jirushi]

Sorry for the late reaction, but thank you 19Sheridan57 and 1900colt. I am getting there, resealing wise. Decided to send the valve stem to Lawrie in England to get a good quality, well fitting polyurethane seal. Hopefully that will work. I must also remove some rust from the seat of the o-ring for the brass valve body, in the cylinder. I think this rust prevents the o-ring from sealing well, which might explain why a leak was developing after 4 pumps, with every type of valve seal I tried.

Anyway.

Great news:
this morning I opened my Instagram, and saw a message from Shimizu San in Tokyo.
He searched through his extensive collection of vintage Japanese airgun paperwork, and found my gun.

It's a

Jirushi Sportsman Model 547

Or perhaps 542, if the last number refers to the caliber (as with Benjamin, for instance. My gun is in .22")

[1900colt]

That's great you found out what this is!

The mystery rifle finally has a name😁😁

[Pellet Fun]

Louis your persistence paid off and your Tokyo contact was a great help. It’s a really nice rifle and deserves its place in history.