Found beat up German Luger dated 1911

[Patrick Chadwick]

Note the precise style of the marking - the Imperial German Army was very picky about this!

R cursive
.
S
.
2 (slightly smaller font size than the S)
.
186 ( slightly smaller font size than the 2)
.

In which case, the interpretation would be Reserve Sanitäts (= medical and sanitation) -Detachement No.2 Weapon No. 186

As a weapon for a medical detachment - i.e. strictly for self-defence only - it would have hardly been fired at all - hence the condition of the barrel being better than one might expect.