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Benji Discovery/Katana POI shifts.. still not what?

May 5 2013 at 10:14 PM
JohnL57  (Login JohnL57)

Ok, so I cleaned up the transfer port and made sure the breech was tight, couldn't slide a thin strip of paper under the breech, tightened the tiny screw. I then tried to mount a barrel band close to the breech, but the band pulled the breech up. I sanded the band with a dowel wrapped in sandpaper till the breech didn't pop up when the band was installed. When I tightened the rear breech screws, the breech tilted enough to open a gap, but I could pull the front of the breech down by tightening the upper set screw. This kind of bent the barrel down, putting some squeeze on the forward barrel band. Things were looking OK for a fill and a half,with around 1/2" groups @ 45 Yds, then the POI shifted left and the groups started spreading way out. I have tried shimming the air tube and action with thin card stock to float the air tube, but that makes things worse. This is of course getting a mite old by now-I'm tempted to part the sucker out, but I know it'll shoot, in between poi shifts, I can do 3/8" groups at 45 Yds, then shoot the push pins that hold the target!
Here's the band in front of the breech:
[linked image]
Here's the action showing the front band:
[linked image]
The front band is tight to the air tube and the barrel is wrapped with a soda can shim all the way around. The upper set screw is just touching the barrel to eliminate play but not all the way tight.
I sure could use some advice on where to go from here, this is getting old!!!

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