Lone Wulf
If your rifle doesn't bear any Austrian marking (in particular the NPV from the Vienna proof house), you most probably own a Mannlicher-Schoenauer that was assembled in the UK by British rifle smiths and proved in London. The symbol with an arm and scimitar over the letters "NP" has been the London definitive nitro (smokeless) powder proof for all guns since 1904. I also own one MS of the British trade, a M. 1908 with serial number 664; it bears the same marking as yours. I contacted in 2015 the London Proof House but they do not hold any archives for early to mid XXth century and could not therefore provide with any information about proofing year.
I hope this will help.
Louis