To continue the story: The power when cleaned up and with a single replacement spring was 160 -190 fps (.22) with some clear air leakage at the swing out breech. Yesterday I had a fiddle and applied a little grease to the breech around the loading port. On firing the power was up to around the 205 mark with grease visibly blowing from around the breech sides. Next up was to apply electricians tape over the breech before firing. Output again up, this time to around 210 (highest was 213 with Accupells).
So... breech renovation time. I was thinking of a delrin one but the breech is approx 7mm thick and my delrin is only 6.5mm. Maybe add O rings around the loading bay? ... not possible because of how close the bay is to the bottom edge of the breech block.
I could have resorted to aluminium or even steel but decided on a trial run with an old faithful of high presion plastic board ... an old kitchen chopping board in a delicate pea green colour. OK, 9.5mm thick but easily worked and I figured that being more flexible than metal or delrin it might be more forgiving and likely to give a good seal, especially as the old breech block was not worn the same all over and I suspect neither was the slot it swung into.
So a couple of hours with saw, drills and files and I had a delicate pea green breech ready to go. Success! Power is up to 230 -240 fps. with Accupells. The new block is a firmer fit as it finally closes into position, the loading bay was drilled at 7/32 (0.218") and provides a nice snug fit for Accupells, Marksman were a tad tight and needed seating in order for the bay to close. I guess a slight chamfer on the bay entrance would sort it.
So, all in all, quite happy with the new Art Deco pistol. and for the purists, I still have the old original breech to put the pistol back in original condition should I need to. I doubt if the plastic unit will last forever ....
I guess I will still look out for a new original breech but do not have much hope of finding one. One day I may set to with a bit of steel; I believe old chisels are a good source.
Cheers, Phil