To digest JSB's, First: The stock barrel usually preffer's a pellet with a 5.52 head diameter.
The stocker also likes speed in the 900 range this applies to both cal. If you are hand lapping JB bore paste can do more damage than good, Try some mothers metal polish smeared well into a paper towel use a .177 bronze bore brush to retain the pre-treated strip of towel that's wrapped around the brush sufficiently to be a snug fit in the bore, Stroke slowly not allowing your patch to exit either end. Six or seven passes then unroll from brush push a cleaning pad thru and resume treatment. Usually twenty-five-thirty strokes is sufficient. For those that can: a flat crown can sometimes improve that barrel that shot like crap, Don't reduce the length of the barrel doing this, It must be done in a lathe with an extreme relief tool bit honed as sharp as possible. Work from the center out leaving a seating ring approx. .080 for the air diffuser to rest on thus keeping the barrel at stock length. Use a speed setting in the 400-500 rpm range and take slow,Light cuts, If your tool bit has sufficient relief you should end up with a finish approaching a polished look. Don't stop there!! Now take a small piece of 600 grit wet or dry rolled into a tube and chamfer the edge of the crown, We are looking for just a slight ease here, Run the lathe in forward and reverse allowing your glass paper to just "ride" the edge lightly.
Remove the barrel and move on to the transfer port, Take a round jewelers file and relieve the sides and forward edge of the thru hole into the bore, We are only looking to smooth this edge sufficient to keep the head of the pellet from being shaved as it passes over the transfer port.
When done and under magnification you should see what looks like a bullnosed edge at the forward portion of the transfer ports relief into the bore.
Now take a dremel with a hard felt cone, You can size these for a tight to snug fit by running them on a piece of rough sand paper when the cone fits with a tight to snug fit your ready to apply some jewelers rouge to the felt cone and polish the inleade, Once again stop every so often and clean then re-treat the cone. With a little work you can get a mirror finish here. Let the cone just enter the lands and grooves thus easing the pellets entry, Allowing it to come to rest in the bore with as little abuse or upset as possible when cycling the bolt.
now go to the crown and repeat being careful not to overheat by applying to much pressure, Clean it all up, Reinstall and begin testing again. Most but not all barrels will see a major improvement with some approaching the LW barrel fo accuracy. Good Luck!!! Regards,
The fact that you took the time to do this write up is awesome.You are truly a gentleman and a scholar.I for one appreciate all you do for us airgunners.