I concur, the Gun Tube & Recoil System are almost certainly the Russian Putilov - base designation is M1902. It does look like a high angle mount. Given the 'permanent' looking emplacement I did wonder briefly about a light coast / beach defense gun, but on a second look I doubt that the mount can depress & may not be able to reach level?
... appears to be the standard pedistal mount develoved by the Germans in 1916. Both the French M1897, and Putilov M1902 were fitted to this mount. Numbers were also supplied to Austria-Hungary. It depressed to 45 degrees ( horizontal ).
Perhaps future qun inquires should be on a new tread; this one is quite lengthy.