There's little info to go on there, but on the face either your smith may be a competent smith, but not a competent hand loader, or you misunderstood what he said. In any event, like said above, if you seated it to SAAMI OAL, then, I'd look elsewhere for the cause of the problem. Seating deeper in the case can raise pressure. Seating further out, has been shown to have little effect on lowering pressure, but can a little bit. Think of it this way...seating deeper decreases case capacity/increases pressure. Seating further out increases case capacity/decreases pressure. I don't hold to the 15% thing on starting loads. In my opinion, 10% should be plenty off of max to start safe in a case like your loading for. Go back, check all your components, load data, COAL, and restart the load. If you're loading well under max loads, and your measurements are right, then it could be a gun problem, like headspace for instance. Eliminate the loading, and your procedures first.
By the way, what is the load you're using?