No headstamp 13.2x99mm Hotchkiss


I’ve had this old, empty .50 BMG lying around for years. I’m sure it’s probably common as dirt, but I am curious as to what country it came from. There is no heastamp, and it is berdan primed (one small off-center hole inside). The firing pin indentation seems odd also. Anyone know? Thank you.


Sure it’s not a Japanese 13mm Hotchkiss?


You know, I just assumed it was a .50 BMG because it looks like one. How close is the Japanese round dimensionally?

Dimensions on this one:
rim: .796"
base: .792"
length: 3.902"
neck OD: .575"
These dimensions are all within a few thousandths of the BMG rounds I have. The shoulder does look slightly forward compared to the USGI brass, but it’s a bit dented so it’s hard to tell. Actually on second look, the neck is definitely about .1" forward.

Japanese would make sense, given the lack of headstamp. I just did a search and found some info on the 13.2x99mm Hotchkiss but otherwise I’m completely unfamiliar with it. I found:

“This weapon used a modified version of the American .50 calibre ammunition, loaded with bullets of slightly larger diameter – 13.2mm as opposed to the original 12.7mm; the cartridge cases were about the same, save for the larger diameter of the neck of the French load.”


“Japan, among others, was so impressed with these weapons that it acquired a manufacturing licence and built 13.2mm machine guns in significant numbers.”

I’m assuming that you are correct. Are these uncommon rounds?


While not exactly scarce, they are not that common. Good find if you don’t have an example. Most I’ve seen have been fired or inerted.


This cartridge was used by the Japanese navy, who also produced Browning machine guns to use it as an aircraft gun. Jack


Thanks guys. It will go in my collection. I’ve had it for years and didn’t have a clue. I think it may have been in with the short belt of fired .50s I got when my grandfather passed away. I think he had told me he brought them back with him from Japan in '45.


Naval 13,2 Hotchkiss (for Shipnoard AA Guns) is headstamped with a Kana symboil for the Naval Arsenal of production, the quadrimester od the year in Roman/ Japanese and the year in Japanese Calendar (two digits) ( Just like Japanese Naval 7,7x56R. very late war production may Not be headstamped.

Army AA ammo is Not headstamped at all ( single and three barrelled Gun arrangements.)

AS to the Naval use of 13,2 in Aircraft Guns of a Browning design, I am unaware that this Occurred…do you have a Japanese designation for the Gun, such as a “Ho” number? ( such guns were considered “Cannon” and not MGs.)

I have a 12,7x81SR Cannon which IS a Browning Copy ( They also made a Browning Copy in 20mm (20x80 RB).

I have one Japanese Naval Hotchkiss case from New Guinea; it was initially mis-identified as a .50 cal, until the Japanese headstamp was cleaned up and decifered. ( “yo” III 99 ( Yokosuka Naval Yard, 3rd Quadrimester, 1939)

With an Un-Headstamped case, the severe Ringed primer is the ID feature ( the US didn’t go over to a ringed .50 Primewr till after the late 1950s, and US cases are headstamped.)

Nice Find, regards,
Doc AV
AV Ballistics.


Doc: I believe the designation of the JNAF aircraft Browning for the 13.2 Hotchkiss round is type 3 (1943); late subtypes of the A6M5 Zero carried three of these weapons in addition to a pair of Oerlikon 20m/m cannon. There was also a JAAF Browning for the 12.7/.5 Vickers-type cartridge. I’m not sure of the designation of this latter weapon, and I believe it was somewhat smaller overall than the naval type 3. Jack