I doubt that it's a stability issue with 240gr bullets. 1:28" twist is sufficient to stabilize a 240gr bullet at well under the velocity that 80gr of T7 will produce. Also, the only effect velocity has on stability is in determining the rate of rotation when the bullet leaves the muzzle. If the bullet has enough spin to be stable at the muzzle, it'll be stable at any range and velocity as it goes down range. The reason is that, while there is a lot of drag acting to slow the bullets linear velocity, there is very little drag acting to slow its rate of rotation (angular velocity). Think about a spinning top (the childs toy) or a gyroscope. When you spin a top it will spin for a relatively long time, more sometimes a minute or more. The total flight time of a bullet is less than one second typically, meaning that the rotational rate has retarded very little.
Also, while there is such a thing as an "over stable" bullet, this is not an issue at the relatively short ranges of muzzleloaders and rifle (except in the case of extreme range shooting...i.e. 1000yards+). The problem with overstability is the tendency of the bullet come down sideways or even base first on the steep long range trajectories because the nose so strongly wants to stay pointed the same direction it was pointing when it left the barrel.
If it was not stablized at all you wouldn't be getting 3" groups at any range, and it you did hit the target you'd see oblong or profile bullet holes because the bullet would be tumbling.
I, personally, think that there is something else wrong. Others have suggested modifying the foreend to "free-float" the barrel (the quotes are because I don't think that it can be truly free floated, which implys NO contact between the stock and barrel). I don't own an Omega, so I don't have any experience with the Omega specific problems.
Another thing you might do is get some real sandbags or a proper shooting rest and bag the gun in properly on the bench.
Attention to detail is critical, especially with your swabbing technique. Since you started with a good group and they got worse from there, I'd think that there was a problem with loading/cleaning technique. Since you are shooting T7 I'd suspect the problem may be "crud ring" related. If you have the crud ring toward the breech end (it usually forms right where the bullet/sabot seats against the powder), and you are not swabbing it out every time, the bullet will seat against the crud ring and not the powder charge, which will cause erratic velocity and poor accuracy. The problem is that, in my experience with other rifles and T7, the crud ring can be so hard as to make you think that you've hit the bottom of the barrel when swabbing, but you have to push through it with short strokes (which is important so you down get the jag stuck in the bore), and then scrub it until you can't feel a change in resistance with each stroke.
Or, as a last resort, you can sell the Omega and the T7 to your least favorite buddy and get yourself a Savage 10ML-II and shoot AA 5744. Excellent accuracy, no swabbing.
[8D]
Mike
got groups
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