If they're shooting apart, barrel time is too long and you need to either increase velocity or decrease bullet weight. However, the limit is (over)pressure and if that happens, you must consider re-regulation of the bbls. (sometimes, changing bullet and powder may help). After I had my FN O/U scoped, I had the same problem and, wanting to stay with the Alaska bullet, I had my rifle re-regulated and fitted with a new (longer) wedge. All is fine now and both bbls. shoot in the same hole at 50 m.