Identifying WWII Japanese Bullet Casings: A Field Guide from Saipan

Eighty years after the fall of Saipan, Japanese bullet casings still surface from the island’s red soil every season. Here’s how to identify what you’re looking at — caliber, manufacturer, year, and why each detail matters.

The Soil Still Remembers

It was a short walk off the main trail, maybe twenty meters into the undergrowth near Marpi Point. The rain the night before had loosened the topsoil, and there — sitting in plain view on a bed of coral dust — were three brass casings, oxidized green, arranged almost as if someone had placed them there.

They weren’t placed. They had simply waited. Eighty years, for someone to notice.

Saipan is like that. The 1944 battle left behind tens of thousands of spent rounds, and unlike Peleliu or Guadalcanal, the island’s erosion keeps bringing new finds to the surface. If you know what you’re looking at, a single casing can tell you which side fired it, from what weapon, and when.

Here’s how to read them.

The Four Japanese Calibers You’ll Encounter

The Imperial Japanese Army and Navy fielded multiple small arms at Saipan, but four calibers dominate what you’ll actually find on the ground.

6.5×50mm Arisaka — The Old Guard

The classic Type 38 Arisaka rifle cartridge. Rimless bottleneck case, roughly 50mm long. By 1944, the 6.5×50mm was being phased out in favor of the heavier 7.7mm, but Saipan’s garrison troops still carried significant quantities. If you find a smaller, slimmer casing with a subtle bottleneck — it’s likely 6.5mm.

Field marker: smaller base diameter (around 11.5mm) and a noticeable neck taper distinguish it from its 7.7mm successor.

7.7×58mm Arisaka — The Standard Issue

The Type 99 rifle round. This is the most common Japanese casing you’ll find on Saipan. Rimless bottleneck, about 58mm long, base diameter roughly 12mm. Heavier hitting than the 6.5mm and designed to match Western service calibers.

Field marker: look for the headstamp at the base — Japanese arsenal marks are typically a small symbol (often a stylized star or arsenal initial) rather than full text.

8×22mm Nambu — Sidearm Rounds

Used in the Type 14 Nambu and Type 94 pistols, this bottleneck pistol cartridge is much shorter and narrower than rifle rounds. You’ll find them around command posts, cave entrances, and officer positions — rarely in open battlefield contexts.

Field marker: very short overall length (around 22mm), small diameter, distinct bottleneck shape.

7.7×56mmR — Navy & Machine Gun

A rimmed variant used primarily in Type 92 aircraft machine guns and some naval applications. Less common on land than the 7.7×58, but present around airfield ruins and anti-aircraft positions on Saipan’s northern plateaus.

Field marker: prominent rim at the base distinguishes it from the rimless 7.7×58.

How to Read a Japanese Headstamp

The base of the casing — the “headstamp” — is where the real story lives. Japanese military cartridges typically carry three pieces of information, arranged around the primer:

1. Arsenal mark — A symbol identifying which factory produced the round. The most common on Saipan is the stylized ✴ (star) of the Tokyo Arsenal, and the 矢 of the Nagoya Arsenal.
2. Year of manufacture — Shown in the Japanese Imperial Year system (year 2600 = 1940). A marking of “19” means Showa 19, or 1944. Most Saipan finds date from Showa 16 to 19 (1941–1944).
3. Lot or batch number — Less useful for general identification, but valuable for matching to known production records.

Before you touch or photograph a casing, note its orientation and surroundings. The spatial context — whether you found it in a cave, on a ridge, near a wreck — often tells as much as the round itself.

A Word on Ethics — and the Law

Saipan is part of the Commonwealth of the Northern Mariana Islands (CNMI), and U.S. federal law — combined with CNMI regulations — restricts the removal of historical artifacts from public lands. Many battlefield areas are also under active preservation or are considered sacred sites by local communities.

My rule, and the rule I’d ask any fellow explorer to follow: document, don’t collect. Photograph in situ. Record coordinates. Share what you find. Leave it where the battle left it.

These islands aren’t display cabinets. They’re the largest open-air memorials of the Pacific War, and every relic in place is part of that memorial.

The Casing in Your Hand Is a Timestamp

A single 7.7×58mm casing with a Showa 19 headstamp, found below Marpi Point, tells you: a Type 99 rifle, made in Tokyo in 1944, fired in the final weeks of the Saipan defense. That’s not just an artifact. That’s a fixed point in one of the largest battles of the Pacific War.

Next time you’re walking an old battlefield — here, on Peleliu, on Guadalcanal — slow down. Look at the ground. The island is still speaking. You just have to know how to listen.