A 1 in 28 barrel is made for saboted bullets and probably won't shoot conicals very well. If he is getting lead out of his barrel from shooting a jacketed bullet, his rifelings must be cutting through the copper jacket. I am not a great fan of the .50 caliber power belt bullets, although others have had success with them. I would suggest to him to get some sabots from MMP and some 250 - 300 grain Hornady .45 caliber bullets, and see if he isn't pleased going that route.
Tell him to sign up to the forum, and he can get all the help he needs.