.303 British "star 97-8 7.7"

It has Japanese looks but is it?

Yes, Japanese.

These two were sold in a Japanese auction some time back by auction user ak43j They are his photos. Both dated August 1937, as is your example.

Neat! I’ve never seen one of those with a headstamp over-stamp before!

The Sar with the circle in it is the mark of Tokyo Ammunition Factory, which took over the buildings of the original Koishikawa Arsenal in outer Tokyo, after 1936, when all rifle production had been shifted finally to Kokura ( 4-cannonball mark, both Koishikawa and then Kokura).

The Other stamps and “overstamps” look like IJN Factory marks ( Shipyard ammo factories)., as is the Date layout.

The early History of the IJN T87, T92 .303 ball cartridges ( for Vickers and Lewis MGs) is pretty sketchy, until 1937 dates…but the T87 Vickers was adopted in 1927, so the ammo was either being imported ( ?Kynoch did supply initial Test and Trials ammo) or made at Tokyo ( before 1936)?

Doc AV

The star dot mark(as some collectors call it) on the rounds above is Tokyo Army Arsenal.

The katakana ‘yo’ mark (ヨ) is Yokosuka Naval Arsenal.

The flaming pot mark on this 1928 dated round is Itabashi Gunpowder Manufacturing Plant. (Again the photo was from the sales listing of ak43j)