Thanks again Garvin. I thought the standard bore was .25 ... but clearly other bores were available. I wonder if .20 was for the American market.

Having been thinking about our rifle (dangerous at my age) I pondered on the metal to metal face contact for the breech and wondered if there was a small gap leaking air. A test on a thin shim (aka a bit of coke tin) showed that the barrel would close with no obvious extra resistance so I duly cut a hole to match the transfer port and tried it. Over a range of shots power went down about 40fps. Quite a surprise. Initially I thought my shim must be blocking part of the transfer port but it was OK. So I abandoned that idea.
Next I tried seating the pellets about 1mm into the bore. Previously I had 'finger pushed' them in, making sure that they were seated below the surface. This time there was a distinct 'nudge' as the pellet seated. FPS went up to almost 300! Wow ... almost a heady 4 ft lbs! This was with H&N field Trophy (20.1 grains I believe) ... cheapest I found at £3.99 for 200.

I may well declare a truce with the rifle now.

Cheers, Phil

Cheers, Phil