ctw,
Like Researcher has said above, and the fellow who responded to your other post, you should only be shooting low pressure, and preferably, 2 1/2 inch loads in this gun. BUT only if the action is tight, the barrels are not dented, bulged, or severely pitted on the interiors, and the tubes are solidly joined at both ribs. Your pictures indicate a cracked and loosely fitting forend. The wood on this gun is old and likely oil soaked at the head. This may not be evident on the exterior. Check it for cracks near the action and wrist (section of buttstock just ahead of the grip before it meets the action). And, as already mentioned, Flues model frames are known to be thin and susceptible to cracking (failure) and today's run of the mill ammunition is too much for these guns. Check for any looseness amongst the barrels and the action when the barrels are on the gun and the forend is off. Krupp is known as good material but doesn't mean loose or 'off face' barrels should be shot.
As for the chamber lenght, you need to have a chamber gauge to measure them accurately.
Hope some of this helps.
-jmc
