OK I'm going to assume that your friend is a fair shot and knows how to shoot. That being said and noting that he's using a lead sled which should eliminate human error and the scope is tight it still could be several things. The least of which would be the scope but not uncommon. First thing I would do is get rid of those pellets and get loose powder and a powder measure. I'm suspecting that those pellets are contaminated/old. During loading make sure you apply consistent firm pressure on your ramrod to tightly compress your bullet/sabot over your powder.
Lately I've been playing with Alliant's Black MZ powder with good results in my Accura.