Testing of the FAT-1 was done at Springfield Armory in 1948 and it was noted that there was a high incidence of rim shear in the T25 rifle. The FAT-1 case was modified by Frankford Arsenal and the rim thickness was increased from 0.049inch. to 0.054 inch. This modified case was designated FAT-1E1.
The FAT-1E1 ball round was given the designation T65E2
Frankford Arsenal had been working on lighter weight, higher velocity bullets since August 1946. The bullet had a flat base and mild steel core and was designated T104. As opposed to the M2 bullet, the T104 was to have a smooth case mouth crimping cannelure. The first specimen below is the M2 GMCS bullet, the second is the M2 with GM Lead core (non-magnetic) and the third is the T104.
This AP bullet was designated T93 during 1945, but was not used on the T65 case, instead it was used in the FAT-1E1 case and designated FAT6. The bullet had a flat base and hardened steel core, with a black tip.
This is the T70E2 designated dummy
T70E2 cadmium plated case done at Springfield Armory
The grenade launching cartridge was designated T116.
The Armor-Piercing Incendiary cartridge was given the designation T101
The designation for tracer was T102 and was the same for the FAT1 loads. The tip colour was orange and gave a dim red trace to about 50 yards and bright up to around 800 yards. The specimen with the red tip was also probably loaded by Frankford Arsenal, but there is no record of why it was done like this, or what the difference was.
The aluminium cases FAT1E1 was a continuation of the contract awarded to Remington in the development of aluminium cased rounds. Cases are coated with a graphite coating apparently to aid in extraction.
From left: AP (T93), Dummy (T70E2), API (T101), Tracer, Orange Tip, Tracer, Red Tip (T102)