Powder can degrade and I have had the experience of T7 doing that to how ever I have shot old pyrodex with out a problem.
I your situation there are certain things I would start with. ALL the mounting screws for the sight system switch scopes [they do go out more on muzzle loaders than other type guns because of the type of recoil.
The next thing is the breach plug the hole size of the tiny hole where the flame goes through to the powder is eventually enlarged by flame cutting and when it get to a certain point the accuracy goes South.
One other problem you might run into with a Omega is the mechanism is fastened to the barrel besides the trigger and hammer assm. the mechanism for locking the gun up is there and there is a possibility it is loosening ; personal experience on the breach plugs and the mounting screws for both the scope and the trigger assm. have come loose on me they have loctite on them now. Lee