Some interesting info on Husqvarna Shotguns. Sweden never had proofing laws because they believed in the product of choice Husqvarna.

From research about the Husqvarna shotguns test program the following conclusion can be drawn:
Guns marked on the barrel "Special Steel" or “Niklstal” are intended for smokeless powder. This information came from the Husqvarna museum.
The proof mark on Husqvarna shotguns can be a small or large letter H with a crown. From this it cannot be concluded whether the weapon was proof-fired for nitro- or for black powder, only that the gun WAS proof-fired. Research into this marking continues.
Some facts:
Generally, the guns were fitted with steel barrels, but damascus barrels were delivered on demand as late as 1908.
Translation of the test program and quality control from the 1902 catalogue.
"When a barrel bursts, or the gun, for some other reason is damaged during shooting, the gun manufacturer, in most cases, gets the blame with the argument that the reason for the damage is use of bad quality materials, or manufacturing flaw. That such faults should exist on guns delivered from us, we consider that we have prevented, partly by using only best quality materials, and partly, and above all, by the most accurate inspections, and rigorous tests. I.e. the barrels on guns delivered from us have passed two firing tests. The first test, made when the barrel has been pretreated, is carried out with tripled black powder charge, and fivefold shot load. The second test, made when the gun is ready for delivery, is carried out with double powder charge and double shot load. If the barrels and the action has passed there tests, without in any way having been altered, they will not be damaged when using normal powder charges and shot loads, independent of the charge being black powder or suitable low smoke powder. Additionally, from each new set of barrel raw material, samples for test firing are taken. This test firing takes place in such a way that the barrel, drilled to cal. 16, and the outer diameter turned to a diameter that correspond to that of a typical 16 cal. gun, is charged with 14,25 grams of black powder and, initially, at the first shot, loaded with 85 grams of shots. The shot load i increased in such a way that, at the 24th firing, the shot load is 456 grams. For the 25th firing, the charge is increased to 19 grams. Firing continues, for each three firings, the charge is increased, for each firing the shot load is increased, until the barrel bursts. Generally, our barrels, made of Swedish steel, will hold a charge of 14.25 grams of powder, and a shot load of 400 grams. Barrels made of special steel will hold a charge of 23,75 grams of powder and 860 grams of shot load."

Top Lever shotguns
As concluded before, Husqvarna shotguns made after 1908 are designed for smokeless powder. The serial number at the end of 1908 was 55000.