The velocity problem is directly related to the powder, my recommendation would be Swiss Black, or GOEX FFF or Pyrodex try P if it blows the patch then try RS. 777 will work some times for some people but a lot have ignition problems with #11 caps.
The accuracy problem may well be a separate problem, you need to find and check your patches after you shoot, if they are blown to shreds as I suspect you need to go to a bigger ball or a thicker patch, may be even both, it is usually the most practical to try a thicker well lubed patch as the first step. If you wish to shoot hunting loads and still have excellent accuracy you may find using a 5 thousands larger ball will make a big difference. Lee