I have found a Beeman C1.
It's a .22 with safety. Serial no. H777695
Tonight I disassembled the gun.

It was difficult to get the mainspring retaining pin out. I think Loctite was the reason. After quite some heating, I was able to get it out with a pin punch.
Also the end block is a tight fit; I needed a pin and a hammer to get it out of the cylinder. It was a bit scary, with the mainspring pushing on the end block.
The gun was low on power, about 7 ft/lbs. Soft to shoot, with quite a light and nice trigger, but the C1 is capable of much higher power.
Apart from rejuvenating the internals, I also need to fit a new barrel, as unfortunately the rifling of this one has 2 deep scratches - it groups like a shotgun.

I had previously ordered a spring, spring guide and top hot from Maccari.
Might also try a spring, spring guide and top hat from a UK seller on , to experience the difference.
The Maccari spring is about the same length as the old one, but stiffer. (The top hat isn't square onto the spring; the spring end isn't totally flat. Not sure if this is an issue. I think that a flat spring end would be better).
I had also sourced new breech seals, a piston seal and a different trigger from Knibbs.
The red piston seal replaces the original ptfe washer. That one has a few scratches on the sides. I've read that some people have fitted an o-ring as a piston seal, but I think this red Knibbs one will work well.

I am used to working on Meteors (I love Meteors!). This C1 is finished to a much higher standard. All edges are smooth. The inside of the cylinder is very smooth. The piston looks nice. No burrs anywhere. I don't think I'll need to do any work with my diamond files, wet&dry and autosol, except for the trigger mech. What a relief!
As a comparison: a photo of the C1 next to my now best performing Meteor, a Mk5 that is very nice to shoot and accurate (2 cm groups at 35 meters and easy plinking at 50 meters).

Cheers