4.32mm US experimentals


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


one of them is listed on ammo-one.com


I have a .17 Javalina Wildcat rd that looks like the round you have and it’s case is 38mm long. Headstamp W-W SUPER 222 REM.



I’m gonna agree with Simon on the 38mm cartridge. Based on the shoulder angle, headstamp, and bullet it is most probably a .17 caliber wildcat.

If Bill Woodin identified the 40mm cartridge as a 4.32 Optimized then that is what it is.

The cartridge link from Yuri is the fairly common 4.32 x 45 which can be found with various headstamps including FA, RA, and LC.



Jim, Here’s a scan of the .17 Javelina.