The forend exerts forward pressure on the bbls,,backward force on the frame when it's snapped/locked into position.
It is pushing the bbls away from the frame.

If there is space betw the bbl face and the frame anywhere with the forend in place, then the bbl's are off face at that spot. even though they can exhibit a very tight fit in the action and on the hinge pin. They are just short of reaching the face of the frame.

IF there is space betw the bbl flats and the action flat (water table) yet, the bbl can still rotate downward a little and it may be enough to close the .003 gap at the one point.
You might not have quite enough room to close it up completely, but at least get rid of some of it. You can always put a bit more clearance down there by trimming the bbl flats. It's only a few .000 but watch what you are doing as the bbls are made to only set down so far.
Remember the firing pins must hit the center of the chambers!
Go too far chasing a tight breech fit and then wonder if the sadly off center firing pin hits will work OK.

Spotting and fitting in the forend any more against the forend bbl hanger will jut make the condition worse as it will then allow the bbls to not only be off face,,but also loose on the hinge pin.
Thats where they start to shuck back and forth and the quick fix is to peen the forend iron on the bottom side to stretch it. That puts it tight once again betw the hanger and the nose of the frame.
It still won't cure any gap/off face problem at the breech.

You either have to rotate the bbls a little more in fitting to make up the gap as above or,
you have to move the bbl back from the hinge pin by enlarging the hook (shim, welding, inlay) or a new oversize hinge pin to move the bbl back those few .000 to allow it to reach the breech face.

Then the refitting once again of the breech face of the bbls to the frame face and probably the forend will need to be refit as the bbl hanger has now moved backward with the bbl assembly and will extra tight when putting on the forend. That's a good problem to have.

It's very difficult to read and feel with hand pressure only wether the action and bbls are really tight. Nothing like a heavy spring closing the action or the forend snapped and locked into place.

One pretty good way to tell if it's tight by using you hands and hand pressure to hold it closed and checking is put the bbls in the vise upside down with the action on it. Having the butt stock attached is even better as it gives you some leverage.
With the unit upside down and held by the bbls up close to the breech so you can tighten them securely,,pull down on the action/stock assembly as if to lock it closed.

You have a lot of leverage there and can hold it closed with one hand while checking with the other hand for the slightest movement around the bbl and frame areas.
Wrap your hand right round the breech joint areas and try side to side movements with the action with it pulled tightly closed.
Your hand will pick up even the slightest movement of the frame/bbl joint at any point.