Chinese bombs 1931 - can someone identify?

[Dreamk]

This is a Italian documentary movie from 1931 (from Istituto nazional Luce - the official documentary/propaganda media of Mussolini's regime) about the civil war in China.
From 00:17 bombs are loaded by Chang Kai Shek partisans under Douglas O-2MC-2 that were delivered to the Chinese central government
The rotation fins of the bombs are very original - the only thing somewhat close to these, that I can remember, is a Spanish bomb produced in the mid 1920s by Talleres de Guernika.

some clips from the movie:


Can someone identify these bombs?

 

[Dreamk]

A much better picture of this bomb on a document dated 1937
I have a strong feeling that the movie and this photograph depict the same event and are both from 1937, not 1931 or 1933 as written in the Luce archives.

The tail seems to be made of 3 fins with a constant angle on their outer edge so they "envelop the bomb and ensure an optimal rotation during the fall.

If correct the date is surprizing as by 1937 the Chinese were mainly using bombs they produced inspired by Italian and Soviet designs or bombs imported from the US.
(Soviet bombs seem to have been used used eclusively by the Soviet "volunteer" fromations in China - TB3 and SB2 bombers)

Are these the elusive bombs produced by Nanking Arsenal in 1934 - either the 40lb (38,5lb) GP or the 35lb Frag ? or the 1931 Jinling Arsenal 18kg bomb?

Judging by the pose of the soldier on teh left, these bombs look a little "lightweight" for 18-20kg - more compatible with 10kg order bombs.