Made the rivet from a scrap of O1 tool steel turned for a "slip fit" with the HW95 barrel pivot block (about 4.9mm) that was unhardened. Now all I have to do tomorrow is use a couple hardened ball bearings on each end of the rivet and my vice to flare the ends a bit so it stays in place.
"It will be interesting to see if your new "ultra tight" barrel will shoot the JSB 8.44gr loosies"
Yep sure will! I'm out of 8.44 grain Exacts but I'll order a few tins just to see. LOL, if they don't work then I can always sell the unused tins like I did before. When I do order the exacts I think I'll order the 4.50mm size since they were more consistent than the 4.52mm size I ordered previously.
"It would be nice to be able to shoot clean pellets right from the tin, with the same or better accuracy and repeatability as the sized and lubed cpl's"
Agreed, however I do believe that the CPLs have a bit higher BC than the exacts. I've been buying Beeman R9s for decades and I don't remember ever getting one that had such a tight leade the CPL needed to be head sized. Now I get a HW95 and a HW95 barrel and both have tighter leades than my R9s. I wonder if HW is deliberately making their barrels to suit the looser fitting pellets like the 8.44 grain Exacts.
"have you ever tried turning any breech seals in your lathe"
Nope, matter of fact after a few decades I've only NEEDED to replace a couple breech seals. A while back I bought an after market "yellow seal" and found that it was too stiff for my taste. I tried another after market brand and found that it was too soft for my taste and actually crushed due to the barrel lockup.
My solution was to revert back to the HW factory seal which I believe you supplied under a "swap deal". I received 4 .177 cal HW breech seals so if you would like a couple they're yours.