This was developed in June 1928 by Frankford Arsenal with a double taper case under drawing FB-9887. This cartridge was also used in the trials to determine wounding power against flesh. It was part of the trials done by the Ordnance Department to investigate sub .276cal. bullets which were done according to a study by the Medical Corps investigating the wounding and shock effect of small caliber bullets.
Bullet at 200% scale.