I'm not the first person to have worked on this barrel and after much agro, my first instinct was to blame the crown, I find that the pellets are being damaged passing over the transfer port. Not something I've ever seen before.
It's probably going to be best to take the back inch off the barrel, turn it down to fit the breech and re-drill the transfer port.
What's the best way to re-drill/mill the port into the barrel with out leaving a burr or sharp edge on the inside?
Tools available:- one bench drill and a lathe with a milling head over the bed (Clark Metalworker).
Any help much appreciated.
On Line Camo in the UK
My Website -http://www.ora8i.rivington-riflemen.org