That sounds very odd considering all the things you have tried - especially the new barrel.
6 Steyr's and none of them putting in a good group at 40m?
I have a few questions...
- What pellets have you tried?
- Have you tried cleaning the barrel thoroughly (VFG system or similar)
- What size group are you getting? - I'm sure it can't be as bad as a shotgun pattern - perhaps your expectations are too high?
- Is the group a random spread or is there a pattern to it - high/low etc?