[Ron Smith]

Mike,

The unit mark doesn't correlate with any known military unit I have ever seen.

My first guess is that it's a Freikorps unit mark.

4.R.1.Frw could very well be 4th Regiment Company 1 Freiwillige (Free Will Volunteers) Freikorps units formed by Nationalist College Students and Civilian volunteers. Ra would be either the abbreviation for the town they were in, or for the name of the unit. More like the name of the unit. The "1" is the weapon number. This would be a very scarce, if not rare unit marking, if I'm correct. I think I am.

I've enhanced the photo so you can see the "r" between the "F" and "w".

Ron