Tis nothing like the originals huh G.T.?...........
The dimpling of the flat of the dovetail is one fix. I have tried it a time or two myself with varying results. My own problem there and the fit that I had to start with.
Of course, depends on how loose is loose.
One can use a round piece(polished flat nose) of stock and hammer; to place a hit on each side of the top of the dovetail(round(?) stock covers the whole top half of dovetail). This is intended to displace the relatively soft material of the barrel proper down towards the bore line, ie squeezing the dimensional criteria of the dovetail if you will, the slanting surfaces downward.........hence more grip on said insert sight. Kinda similar to pinging the shoulder of a barrel for timing in some instances.
Use of the hammer is of course subjective, not talking Jethro type blows, common sense should prevail if the result is going to be ok or not(remember barrel steel is pretty soft). I have no place to talk on hammer useage, but to start with lighter blows is more better.