If this is a contract case - good luck determining the maker. I don’t understand why they would go to the cost and extent of making this huge headstamp identification of the Principle Arsenal of BA when they wasn’t one- Who would care ?
Usually these elaborate headstamps made under contract in Europe in different languages identify the European maker in the local language NOT a ficticious local arsenal which doesn’t exist. These could have been made on contract to be LOADED at the principle arsenal in BA. You are certainly in the best place to answer that question.
Finding ammunition in a country tells you very little to nothing about where it was made or for whom. In addition trying to link projectiles to Navy guns may not be successful as the military at the time had guns for the following missions many of which were different; 1) Navy-large and small boat, 2)Coast defense-large and small caliber,infantry, Artillery units-large and small, cavalry and mountain. In addition there were many local and regional units which could be armed with contract or suplus arms from any country-seldome with first line weapons as used in the standing military. So- determining what projectile goes to which gun is far more difficult than just finding out which guns were of record in use at any one time.
I am trying to get the artillery ammo collectors to come on line more seriously but not too much luck yet. They will come.