You might have to swab between shots. Also I am sure you are, but are the maxiball lubed? I had a neighbor stop over once and said he had a hard time loading maxiball so when I had him show me, I noticed he did not lube the bullet.

If you want to stick with big lead, look at the 460 grain No Excuse Conicals and start them around 80 grains of powder. They might shoot good. Also some Great Plains with a ballistic sub base might be a good combination.

Make sure you swab. Your rifle might be going through a breaking in period. Also the powder you are shooting is known for hard crud rings and they can cause loading problems. It is still one of the best powders out there, crud ring and all.. (besides Goex )