Just say a prayer to the Almighty, and give it a solid whack with a piece of shim stock and a ball peen hammer. If still loose, take a prick punch and get up close near the sight, left and right, fore and aft. If that fails, send it back to those experts and demand a new barrel.
Again, that dovetail need only be deep enough to hold the sight. 1/2 of the contemporary work that I have seen has sights that are cut in way too deeply. Incidentally, look at the base of your next front sight; it is a rough part. Chances are you can do away with a lot of that mass and lower the profile.
Also, these front sights that look like the sail on Teddy Kennedy's yacht are not at all consistent with most originals from Pennsylvania; take a look the real ones. Store bought parts are rough parts, meant to be worked to look real. I often remove up to 90% by weight from a rough part, and we soon learn to make our own. Store bought parts usually end up looking store bought. Conversely, around this general region, those who make their own usually know what they are doing.