The $100 challenge.....

Well I think I've gone as far as I can with this thing.  I was wrong about the offset difference between the port and the barrel.  There was a little difference, ut not enough to be an issue I don't believe.  However that would have been corrected when I eased the breech with a nice sharp flat file.  I set the gun up in the vice with a machinist's level and then took several careful wipes with the file and checked the barrel for level.  It only took about 3 attempts and the barrel was aligned with the cylinder.  I was still having trouble getting the cocking shoe to engage in the piston slot properly so I used an old chisel to spread it open a bit and then cut it back with a carbide burr and then a sanding ring in the Dremel to narrow it down enough to fit in the cylinder slot.

Got it all back together and mounted the Tasco scope, but I'm still not doing very well at 10m.  The gun is nice and tight and straight, but I've tried 12 different pellet types tonight and none is performing much better than the others.  It may be the operator, but I can do pretty good groups with the Cometa Fenix.  I might try adjusting the trigger as I've noted that it seems to have a bit more travel than earlier on and I'm pulling the shots on quite a few occasions.

My barrel appears to be good and straight but it tilts down from the cylinder so there's no point in putting a scope on the dovetail grooves at this stage.  I was the same as you Kruza, I couldn't see the target through the iron sights, that's why I set up the red dot.  I did think of fitting an aftermarket fixed sight but my eyes aren't great either and the red dot is really easy to use with my glasses on.

However, I think I've found a potential cause of my pellet spread.  I looked at the breech this morning and took some measurement on the port position vs the barrel.  They don't match by a long way, I'd say less than 50%.  That probably explains why I can get reasonable groups at 6m but not enough power to do that at 10m.  I'll take some photos and give some measurements later on.  I want to straighten the breech anyway so I'll do that first then match the port to the barrel.