I am particularly interested in the US experimentals of the 60’s and 70’s and have recently picked up a cartridge which I suspect belongs to that era but I am struggling to identify with any certainty. I would describe it as a 4.32mm x 38mm and I have found a very similar cartridge in one of Peter Petrusic’s very old lists in which he describes it as a US experimental formed from a 222 Remington loaded with an 18 grain hollowpoint bullet. The case is blackened from being repeatedly reloaded. This is the only reference I can find to this cartridge. My guess is that this was part of the 4.32mm x 45mm Serial Bullet Rifle project but can anybody come up with a more definitive answer?
I also have a very similar 4.32mm x 40mm cartridge - reformed 5.56mm? - which Bill Woodin identified for me as a 4.32mm Optimized and I would really appreciate any further information on this cartridge.
Pictured are; 4.32 x 38mm, 4.32mm Optimised, 5.56mm for comparison.
Headstamp of the 4.32 x 38mm.
Headstamp of the 4.32mm Optimized