Lahti1935A,
Let me complicate your life a bit more.
Merely knowing the chamber length and steel type does not give any indication as to the service load. Certainly proof marks give us a starting point. The condition of the gun also plays a factor. In regard to
Husqvarna in particular, a short example. Some time ago I purchased a
Husqvarna M51 12ga. It was in great shape. I even had it recase colored and reblued. According to the serial number, it was produced circa 1943. Well, I had a special project in mind. So I started looking for a second set of barrels for this gun. I found a donor gun, again a M51 12ga. The serial number corresponded to circa 1946. A 3 year gap, I felt lucky. Until I tried to exchange the barrels. The later gun was not the same at all. They had "beefed up" the frame and the barrels in those 3 years. There is no way to fit the later barrels on the earlier gun. The proof marks were exactly the same by the way.
Another personal story. I found an early pre-Fox in terrible condition. Just the thing for a complete restoration. Sent it to a gunsmith I trust. After he disassembled the gun, he found a crack in the interior of the frame. It has since been welded.
A gun really should be given a good inspection by a gunsmith who knows these guns and can take the proper measurements. Not only chamber length and bore diameter. But also the wall thickness of the entire length of both barrels. If a thin spot is found it should be marked and the thickness noted. Having a thin spot 3 inches from the muzzle is very different than having it just beyond the forearm. One is most likely shootable, the other is cause for concern.
You are asking the right questions. Continue to ask. We are all still learning.
Pete