7x20mm Nambu cartridge questions (Japan & Thailand)

A week ago I bought a small bag of assorted cartridges from a local collector and found a few gems (at least to me) among the mix. Among them were a 7.9mm B-Patrone, a pair of P.m.K.-v.-Trop’s, a WW1 dated 8mm Roth Steyr round, a 1913 dated .45 ACP, and most importantly, a 7mm Nambu round.

It is brass cases, with cupro-nickle jacketed bullet, which appears to have been press crimped into the case. The primer is brass. I have a couple of questions about this cartridge. I know that the 7x20mm was manufactured in both Japan and Thailand. I can tell my particular cartridge was made in Japan, but I don’t know what arsenals/companies made the Baby Nambu ammo. Japanese Military Cartridge Handguns 1893-1945 states that 50 round boxes marked both 1st Tokyo Arsenal and Tokyo Army Arsenal. So I have the following two questions:

Does anyone know of any other Japanese pre-war, or war-time producers?

Secondly, I’m curious to know how uncommon these rounds are, as I’ve heard that they’re as rare as the pistols themselves (a claim I find dubious at best), and would really like to know for certain.

I do not know of any other Japanese ammunition factories that made the 7 mm Nambu cartridge in Japan. Information on the subject of Japanese ammo factories is sketchy at best. Much material was destroyed during WWII, perhaps more so than in Germany, because of the structures of buildings and the huge amount of fire bombing that was done. Secondly, the Japanese concept of “a factory” was somewhat different than many of us think of the subject. Many of their factories were spread all over an area - almost “cottage industry” - rather than contained in one building or a single complex of buildings. I would think, though, that by the nature of ammunition manufacturing, that the Japanese ammo factories were perhaps a bit more confined to single buildings or building complexes. Third, of course, is that production of the Baby Nambu pistol itself was fairly low, and of course, that would reduce the need for cartridges and multiple cartridge-producing facilities for this caliber.

As to rarity, I would call the cartridges “scarce” now, rather than rare. Occasionally in not too many years passed, even some full boxes have shown up, bringing very big prices (500.00 up) and often ending up with a gun collector to go with a pistol, rather than with a cartridge collector.
I have a complete Baby Nambu outfit captured in the Philippines by a friend of mine during WWII. He had fired the rounds left in the two magazines, but all 14 of the cartridge in the loops of the holster. were still there. I have them with the pistol, although due to verdigres, I have long since removed them from the shell loops. I did want to obrtain another 14 for the magazines, once I became financially able to buy that many five buck cartridges, about what they brought at the time.
I then had no particular problem finding that many, out side of my actual cartridge collection, within the space of about a year. Obviously, it was a casual effort as well, not exactly an emergency need to find them.

There are variations in the cartridges, as would be expected for a round probably made for about 40 years. Rim thicknesses, shape and size of the extractor groove and bevel, and so on. Also, they are known with and without the stab bullet crimps at the neck. To my knowledge, all of the ball rounds made in Japan have a CN bullet. I forget off-hand what jacket my factory dummy round has.

Boxes are now hoard to find. I was able to find a box with a few rounds in it, perfect for the way I prefer boxes (empty save for one round to show original content of the box, since nothing is learned from the other 49 rounds in most cartridge boxes). I used the couple extra ones in the box for trade years ago, when I acquired it.

Rounds were made in Thailand, many with GM bullets and even nickel primer cups. There is an all-blackened round also, that may be a dummy. I seen a few in collections, but I have never pulled the bullet on mine to see if it has powder or not. Total cartridge weight is inconclusive. They are simply too rare for the rather “dicey” act of pulling bullets out of old pistol rounds (split necks sometimes the result of pulling, or putting it back in) and I would not risk that under any circumstances. Some of the Thai rounds have the look of having been made with totally refurbished .30 Carbine cartridge casings. Of course, Caveat Emptor on those, as it is the case used by those few reloaders of this caliber to form the original caliber. I have a couple of samples of those, one from a good friend who used to shoot his Baby Nambu with some regularity. I wish I had obtained his dies and components left when he passed.

Well, I wish I had some good solid information for you, but that is about all I know about the cartridge. I guess I should add that I have an unfinished aluminum case that could only be intended to have been made into 7 mm Nambu, but I would discount it as anything more than an attempt by a handy reloader to make some cases from scratch. I also have a red wood bullet blank, but unlike the 8 mm nambu version, I found these in a dime box at a gun show and they are, to me anyone, obvious fakes. I kept them only because it interested me that anyone would go to all that trouble to make them.

Hope this has been of some assistance, anyway.

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Just to complete the thought…my 7mm Nambu dummy has what appears to be a hollow brass jacket.

Jon - I think mine does too, but I have been back and forth to the Hospital, where my wife was until a few hours ago, and very preoccupied, and have not been my collection room for a couple of weeks. Everything lately is off the top of my head or it doesn’t get said.
Hey, that rhymes.

Interesting to see what a full original box of this 7x20 Baby-Nambu ammo goes for these days - $1826.00 !! The box does look to be in amazing condition, and the cartridges as well. This same seller also had a full box of 9x25 Export Mauser which went for over $150.




Wow! I would assume someone has a firearm that they wanted a full box of cartridges to accompany

From: https://mobile.twitter.com/Farman12We18WdT/status/1388874438423179265/photo/1

Text and photo posted by: [ け64@Farman12We18WdT ]

Google translation:
"It is said that the 7x22mm Nambu bullet of the Nambu small pistol produced in Thailand has a longer neck and a copper jacket than the Japanese one.

By the way, the Japanese original is a cupronickel jacket."


It is interesting to see another specimen of he weakly-blackened 7 mm Nambu cartridge. I have one in my own collection, and it does have a longer neck than a typical Japanese-made round of the same caliber.

Overall Case Length:

Original Japanese - .769" to .779" (19.55 to 19.80 mm)
Black Case round - .826" (20.98 mm)

My specimen appears identical to the one pictured. I weighed this, and a non-blackened ball round, definitely NOT Japanese, with GM FMJ RN bullet, said to be from Thailand, and came up with a wide range of measurements:

Original Japanese ball cartridge - 6.77 Grams (104.5 Grains)
Non-Blackened possible Thai Cartridge- 7.41 Grams (114.3 Grains)
Blackened possible Thai Cartridge - 9.55 Grams (147.3 Grains)

The lengthened case could account for some difference in the Blackened-case round, but I would not think it could be 33 grains!

Both of the cartridges in my collection believed to be Thai have almost identical shoulders and extractor grooves and bevel. However, the blackened bullet is somewhat more pointed than the other. Both have GM (non-magnetic) bullet jackets. While both have primer cups of brass and not typical in appearance with Japanese primers, and while both cups are flat, the flat portion of the cup in the blackened case round goes right to the edge of the primer pocket, while that of the other presumed Thai cartridge with no blackening of the cartridge has a slightly rounded edge to it.

While Thailand is a very possible source of these rounds (it is known that they had strong economic ties with Japan, and purchase a lot of armaments from the Japanese including Nambu Pistols), I have yet to see any strong documentation of Thai-made Nambu cartridges in either the 7 mm or 8 mm caliber. If anyone has documentation, aside from mention in American books (unless thoroughly documented there), I would like to hear of it.

By the way, I have not even the slightest guess about why the black-case rounds have a longer neck than any other 7 mm Nambu cartridge which I have encountered, regardless of the manufacturing source.

John Moss