There is very little chance of a bulge like that getting any worse. The Hawken barrel tapers little or not at all, so if it was caused by an excessive charge or an excessive projectile weight (both very unlikely to happen with black powder) it would be right at the rear of the barrel, where pressure is highest. It would also be more elongated than the classic short ring bulge. That is caused by the buildup of gases when the bullet decelerates on hitting an obstruction.That shouldn't get any worse unless you have another obstruction there.