Need help identifying mark

[alvin]

Regarding R/W, it's not singular. Here is another example, Mauser s/n 920498 Selbstlade, which is also the Mauser with biggest s/n that I've seen so far. I don't have Gun Report at hand.... if I remembered right, this is also not far away from the biggest s/n that has been observed by Schroeder. It's circa 1939.

I would believe it's a subcontractor mark. There are a few types of mark on this position, "M" is common, probably means Mauser made barrel. "S" is also observed on late 1930 barrels. WWI era six-point star, etc.

Please note the R/W on this barrel: