Thought I would do a update with the information I have found. The stamping I believe is a 'AO' in a circle. Looking online I have found reference to these being ItalianCaptured M95s (which would make sense, as it is still in its original caliber, but has received some rebuilding which was common due to the amount of M95s captured by Italy). Most the Italian M95s are marked 'AOI' and were used in Italian East Africa (which is what the 'AOI' stands for in Italian), but apparently some weren't used there (I have found reference to some being used in Libya for example), so 'AO' could just be another province that it was sent to.
At least I now know that it was captured by Italy either as post-war respirations or during combat (both are equally likely, as it was manufactured in 1910 it would have been around for the whole war so it could have been captured on the battlefield).