There were two major concerns about the T65 cartridge. Firstly Frankford Arsenal was concerned about the neck length being too short which might result in the bullet not being held firmly enough with rough handling. The US also introduced the T25 rifle and Springfield Armory was concerned about the possible extraction problems with the new rifle. The T65 case was redesigned in early 1947 with an increased case length (increased by 0.08inch) and an increase in the extractor groove (increased from 0.033inch to 0.06inch). A star was added to the headstamp for identification purposes. The rim thickness is 0.049inch. and careful measurements must be done to distinguish the FAT1 from the FAT1E1 case which had the rim thickness increased to 0.054inch.

Although not the focus of this website, there is a very good article done on the development of the T25 rifle. This is the LINK

   GMCS Core                            GM Lead core

   The dummy is designated T70E1


The observation round was designated T103. This was originally designated for the T65 case, but these tests were suspended and reassigned to the FAT1 case with testing done at APG in late 1948 and into 1949. The bullet was by Winchester and has a yellow tip and was patterned after the German B-Patrone observation round.

  Observation (T103)