I do two things to check for this condition in top-lever guns. The first is to push the top-lever hard over with the thumb and hold it there, while supporting the barrels in the closed position. The tip of the index finger is then placed on the join of barrel and standing breech, and the barrels moved from side to side. This should probably then be repeated with the forend removed, taking care not to drop the barrels!

The second check is performed with the gun upside-down and horizontal with the forend removed. Holding the gun firmly by the wrist and/or buttstock with both hands, the top-lever is pushed hard-over, and the whole lot given a gentle shake from side to side.

If there is no movement detected during both these tests, IMHO the gun is tight and 'on the face'.

This assumes a visual inspection for shims and/or peening/squeezing first, of course.