This ammunition was loaded during the experiments that led to the adoption of the CETME rifle and the 7,62 x 51 cartridge in Spain. The rifle, along with a reduced power cartridge (known as the CSP-003) were finally adopted in 1958 and mass produced; later, a full Nato version of both rifle and cartridge would be adopted in 1964.
My guess is that by ‘T-65’ the Palencia factory was trying to designate the new 7,62 x 51 round, not that the load resembled the american one. Note that the box mentions “caliber 7,92 mm”… the force of inertia.
This cartridge has a long boattail bullet with a composite core: aluminum front core and iron rear core. It measures 32 mm and weighs 8,5 grams. The bullet jacket is 90/10 brass (gilding metal).
Two headstamps are normally seen for this round: (FNP 7,62-955), no primer seal, and (FNP 7,62-956), red primer seal. Also, samples may be found with the bullet crimped at the case mouth or not.