Good set of early German proof marks, eagle (preliminary) crown over U (final) and crown over W (choked barrel). The absence of a date stamp usually indicates a pre-WWI weapon. Starting in 1912 there should have been a 70 next to the 12 if the gun was chambered in 12/70. If it's pre 1912 is should have a stamp with the proof load somewhere which you don't seem to have, so my guess is a 12/65 gun made sometime around 1914.
F 135 - the right choice