I've used the 255 gr. maxi-hunters in my Seneca, but I haven't really ever used them in my Cherokee. I use 70 gr of ffg and it'll keep a pretty good group out at 50 yards plus some. I cast my own with a T/C maxi-hunter mold, but I have several packages of T/C cast maxi-hunters that I can't get to work at all. They do as you say and pretty much spray all over. Thay are also noticably harder to start (very much so), so I believe they are a bit different in diameter. I can shoot 5 of them and get no group, but shoot 5 of mine and the groups tighten right up.
The other thing you might do is start playing around with your charges a bit in say 5 grain or smaller changes. You may find a sweet spot. I stay at 70 grains max even though the T/C manual says 90 grains maximum. I've seen too many Seneca and Cherokee stocks with splits near the lock and wrist and I'd hate to crack mine with too high a load. I've killed 2 mulie bucks at about 40 - 45 yards each with mine and though neither bullet went clear though, they were pretty clean kills.
Don't forget to try round balls too. They seem to shoot really well and kill well too. You do need to keep your shots a bit closer and put the ball right behind the shoulder, but the one mulie doe I've shot with it dropped like a rock using a pretty light load of 50 gr of ffg.
Keep after it, you'll find the right recipe.