Ok, did my own research, now you all will know too! =)
In 1300AD a large castle was built to protect Oslo, Norway. It was a fortress and royal residence to the Norwegian sovereigns for many centuries.
There are quite a few references to them producing guns, gunpowder, swords, etc and even exporting them. Here is one example (Link) from 1808 in a Danish “Announcements from the war archives.” Here it is referred to as the “Christiania Arsenal.”
From that time on there are many references to it being an arsenal, an example being The pocket gazetteer of the world: a dictionary of general geography, from 1888: It said it is an arsenal, citadel and cathedral. (Link)
It was also notably used as a prison, in the Letters on Sweden Norway and Denmark it talks of the arsenal where prisoners were imprisoned to “labour in the castle, or rather arsenal at Christiania” It footnotes that to define the arsenal later on page 178 as: “castle, or rather arsenal: Akershus, the fortress of Oslo” (Link)
Here is an image of the Armory Door
And then finally, the most compelling proof and information of an ammo-producing arsenal in Oslo is that the Christiania arsenal is the precursor to modern-day Raufoss! From Raufoss’s corporation’s webpage, on their history, (Link), it quotes:
Development at Raufoss
It all started with the establishment of a match factory at Raufoss in 1873. After a third fire in 1893, the burned-down factory building was rebuilt, but the owners had lost faith in further operation.
In 1892, a defence commission proposed to move the production of cartridges from Akershus Fortress in Oslo to a safer inland location (this due to conflicts with Sweden). The match-factory lot at Raufoss was chosen because it was considered to be a safe location, on the western side of Lake Mjösa, far from the Swedish border.
In the course of 1895, adaptations to the buildings and transfer of machinery from Christiania (Oslo) were completed. The production of 6.5 million cartridges at Raufoss could start. At the end of 1896 the factory employed about 90 workers, of which the majority followed from Christiania. The conflict with the Swedes increased towards 1905, and more production was moved to Raufoss. For some time the number of employees was up to a total of 500.[/quote]
The A under the crown on that pinfire headstamp makes a lot more sense now if it was referring to “Akershus.”