JD Pedersen started the development of his cartridge in 1923 at Springfield Armory. The first rifles were made in 1925, so test barrels were used in the beginning. There were a number of changes to the case as well as many different bullets were tested. The first case type was known as CC-1 with 1,9” case length and had a severe body taper with very little shoulder, which resulted in split cases on firing.
The taper on the case was reduced and in January 1924 the new design was called PD-11, with case production starting during May 1924. It retained the same case length, but had a greater powder capacity as a result of the reduced body taper and more distinct shoulder. The PD-11 also used the small Monel primer. The first specimen has the slightly modified extractor groove that was changed in September 1925, while the second specimen is a pressure test load.
In the beginning of 1926 the case was lengthened by 0.125” and named the PD-42 case. This is what became known as the ‘standard’ length case with the small primer. The brass primer cups were replaced by monel which was a better design.
The first specimen is a tracer load (non-magnetic) and was called the T1. The tip was painted black, which was not appreciated by the top brass because it looked exactly the same as the armor piercing version. The second specimen is a flexibility test to avoid extraction difficulties and ruptures during machine gun firing tests. Last specimen is a dummy load.
In 1928 the primer pocket was modified to the larger noncorrosive brass primer and this modification was called the FB-9892 case. There were initial concerns by Pedersen that the larger primer would weaken the case head, but tests showed that not to be the case. The bottom specimen is an armor piercing round (magnetic) and identified by a black tip.
BRITISH MANUFACTURED SPECIMENS
The A-11 was based on the PD-42 and was loaded in May 1928. The case had a different taper than the PD-42, although the difference is very small and the case wall thickness is also different. The A-11 can be identified by the headstamp ‘F A R’
This case was developed during March 1929 that has a semi-rimmed case with the same diameter as the .30 M1 (30-06) this cartridge with the larger rim diameter was developed for testing in the T2 aircraft machine gun which was then equipped with the Cal. 30 bolt mechanism as well as later tests at Aberdeen Proving Grounds with a .276 Lewis machine gun.