Good catch on the >>RM<< pointing towards Römerwerk / Römer & Compagnie / Röhmer und Compagnie. It has the mm stamp as well as a Bullet weight of 7 grammes or similar. And there is some odd stamp just under the mm stamp. But it doesn't wear a Nitro stamp. So with the stamps @ hand, I would hazard a guess for the date being right around WWI. Too, there is a K in a jagged circled, ratchet, whatever that points to the tubes being formed by Kelber or Klett.
Those white additions to the grip cap & buttplate are more than like post WWII additions so more than likely there was some modification post WWII.
Hochachtungsvoll,
Raimey
rse
