Question: Were guns a valid weapon in duels?
About the article "Shooting", section "Practical uses".

Candidate passages:
Buying guns.
Changes due to the Schengen treaty.
The rules laid out above were changed on 1 December 2008 as Switzerland joined the Schengen treaty; and all member countries must adapt some of their laws to a common standard.
Following the draft of the Swiss government for the new "Waffengesetz" (weapons law), these points will change: Unlawful possession of guns will be punished.
Gun trade among individuals will require a valid weapon acquisition permit.
Weapons acquired from an individual in the last ten years (which did not require a weapon acquisition permit) have to be registered.
As a central weapons register was politically unfeasible, the authorities hope to get an overview of the market through this registration requirement.
Every gun must be marked with a registered serial number.
Airsoft guns and imitations of real guns will also be governed by the new law.
While the above mentioned "free arms" remain exempt from the weapon acquisition permit, the vendor is required to notify the local arms bureau of the sale.  
57 55 J was accepted for use as training weapon in 1950s because of a lack of suitable training guns and no funds to buy new ones.
The old 57 mm Nordenfelt and Hotchkiss guns were worn-out, and 76 mm guns were kept in reserve, so 57 55 J, among other old guns, was used as training piece.
Some of the guns were converted for sub-caliber training for the 234/50 Be and 305/52 O guns.
The guns were refurbished at beginning of the 1960s and sub-caliber guns were converted back to the normal configuration, but the guns were removed from use and placed into storage in 1965–1966. 
Two prototypes were presented to the CABA, 30 November 1956 for a first prototype, the second was sent May 28, 1957.
It contained only a few detail improvements, made as a result of tests on prototype # 1.
On 27 June 1957, three machine guns were sent to complete the CABA.
Two copies were for the Technical Section of the Army.
The weapon was found valid in its presentation and its operating principle, but it could be mounted on all military vehicles in service because of its shape and organization (no handles rear).
On December 10, 1959, the prototype No.
7 and 8 were given to the Atelier de Construction d'Issy-les-Moulineaux for adaptive trials on a circular troop transport vehicle.
Ultimately, 12 prototypes were ordered in December 1956 made and experienced.
The weapon remained as the prototype for the development was not considered necessary. 
For the remainder of the battle, the Germans did not try to storm the fortress again.
Fighting consisted of aerial bombing of the fortress, duels between the fortress' guns and German field artillery and skirmishes between German and Norwegian ski units doing reconnaissance and bringing in supplies of food, ammunition and fuel.
To counter German guns placed in the positional guns' blind zones, the Norwegian artillerymen positioned their two 8.4 cm field guns to cover areas the fixed guns could not reach.
Over the days, the Norwegian guns targeted machine gun nests, gun positions, command posts and ammunition depots in the surrounding area.
On 23 April, one of the 7.5 cm positional guns was knocked out, one of the fortress' command towers was destroyed and the water line was broken.
The second 7.5 cm gun was destroyed on 24 April.
The fortress was under constant artillery fire and held out chiefly to be in a position to support the allied offensive expected from the north.
On 25 April, the Germans employed a new weapon against the fortress when a seaplane dropped a bomb, annihilating the houses outside the walls with shrapnel ending up in Hegra village several kilometres away.
From 29 April, the artillery bombardment steadily increased in strength, with German guns reinforced by captured Norwegian howitzers from the armoury in Trondheim, and the next day one of the three 10.5 cm guns at the fortress was knocked out.
During the siege, a total of over 2,300 shells rained down on Hegra Fortress. 
Manual mechanism.
Revolver action.
While some early long guns were made using the revolver mechanism popular in hand guns, these did not have longevity in the marketplace.
Although the revolver mechanism was fine for pistols, it posed a problem with long guns: without special sealing details, the cylinder produces a gas discharge close to the face when the weapon is fired from the shoulder, as all long guns were.