I have had this round sometime and was told its just an experimental. I have been unfortunate to get the late Tony Edwards collection in 7.92 Besa, and can not see anything which matches this. My feelings is it is made from a old .303 case. Any help would be great, thanks paul.
It looks like a 7.7mm semi-rim Japanese round to me.
Gravebelly is correct, see: viewtopic.php?f=8&t=7536
Many thanks, it was bought as Experimental…! did not pay much so its not the end of the world…yet!