If you are useing butter patches between shots that is probably your problem with throwing your 240 sabots.If you are using sabots you don't want to lube the barrel.
Try just licking a patch on one side and running it down the barrel.and back out,turn the patch over and run it down and back out and see if your groups don't get smaller.
You didn't say what bullet you were shooting in the 240 but my muzzleloaders will shoot the 240 or 250 very good with 100 grs of powder.