6,5mm Japanese Arisaka Ammuntion Dimensional Revelations (Photo Heavy)

[andiarisaka]

I was wondering what the diameter of the head is down there at the bottom of the extractor groove on original ammo. Jmoore, the OP, is going to try to get the measurement for me. I'm having a slight feeding problem with the ammo I form from 30-40. It isn't a problem at all with spitzers, works fine, but I have a cast bullet with a small flat nose that hits the bottom edge of the chamber when the bolt starts forward. It appears to me that if I had a proper depth extractor groove, the round would pop up into the boltface sooner and the bullet would chamber without hassle.

[jmoore]

Will try to get measurements in the next day or so. But if anyone else wants to jump in first, please do!

[andiarisaka]

Hmm, noting that the primer crimp on some of the military ammo you have was smashed in chambering, I'm wondering if the rims were intentionally made thinner to allow for that crimp. Hatcher's Notebook, pgs 438-439, explains how a semi-rimmed cartridge is meant to headspace, and gives a rim thickness of .060" for the Japanese M38 ammo. Could be they didn't always crimp, but it may have been necessary for MG ammo. Incidentally, there was a lower powered load necessary for the MG which was also used by snipers for its lower muzzle flash. I need to get some washers and find out just how much space there is between boltface and the rim seat that Parashooter illustrated so well. A way around the too thin rim for the reloader would be to expand the neck to 7mm, then size in the 6.5 Japanese die just enough to allow the bolt to close. One would then be headspacing on the false shoulder left and the rim would be against the boltface. I think I'll do that with a Type I, which has a tighter chamber than a type 38 so I can use up this Norma brass I been packing around since the 80s. (The Type I doesn't headspace the same way the Type 38 does, but I want be sure the shoulder is out where it needs to be.)

[andiarisaka]

I have a Nogoya series 4 carbine with a matching # bolt and decided to see just how much space there was between boltface and the rim seat. With .074" in shims, the bolt would easily close, with .077" in shims, the bolt stops about half way down. So even if one was using a case with a .060" thick rim, there's still about .015" in play. When a case with a .050" thick rim is used, if it doesn't make contact on the shoulder first, then there's .025" in play fore and aft. Quite a difference from the US standard of .004"-.010". To that could be added (or in some case subtracted) the difference that comes from a mismatched bolt.

[jmoore]

Did some measurements around the groove area. They seem to match published info.

Rim OD: 0.474"
Base OD: 0.448"
Groove OD: 0.414"
Groove width (Full depth): ~0.032"
Groove width (OAL including chamfer): ~0.040"

[andiarisaka]

Thank you Mr. Moore, hopefully cutting an extractor groove that's larger than the itty bitty one the Krag case has will improve the feeding of my over groove diameter cast bullet. You know, the whole idea of the undersized bullet, oversized bore, may have been to keep pressure down so the undersized brass didn't fail. The thousandths shaved off an individual round would add up to a lot of saved material over the course of several million rounds.

I'll keep in mind something I read about a Blake rifle that used a rimless 30-40. The rifle failed because the extractor groove had been cut too large, which is why I didn't start without some kind of data to go by.

[jmoore]

Hmm, noting that the primer crimp on some of the military ammo you have was smashed in chambering, I'm wondering if the rims were intentionally made thinner to allow for that crimp. Hatcher's Notebook, pgs 438-439, explains how a semi-rimmed cartridge is meant to headspace, and gives a rim thickness of .060" for the Japanese M38 ammo. Could be they didn't always crimp, but it may have been necessary for MG ammo.

Most of my Japanese milsurp ammo has been on five round chargers (clips) in fifteen round boxes. All of that has had the three stake crimps. Almost certainly intened for rifle rather than MG use.

[andiarisaka]

This reduced charge 6.5 mm ammunition can be identified by a letter "G" in a circle stamped on the outside of the ammunition packaging which stands for the first letter of genso - the Japanese word for "reduced." This special ammunition was also issued to soldiers carrying the Type 96 light machine gun introduced in 1936 and to snipers issued the Type 97 sniper rifle, introduced in 1937. The advantage of the reduced charge ammunition to the sniper was it aided in his concealment as the reduced charge rounds produced less muzzle flash than standard rounds and thus did not give away the sniper's position.

Some of the MG ammo was fed into a hopper via stripper clips too.

[arado]

This thread piqued my interest. I remembered I have a partial case of Chinese issue 1950 6.5 Arisaka on strippers. Dug it out. I will measure charge, weights and dimensions. I remember it shot very well as Chinese ammo will. gary

[jmoore]

A random 6,5 box top: