Japanese Militaria at Castle-Thunder.com

[Smokey]

I slugged mine, and it measures 0.261 across the flats (lands?) and 0.271 at the corners (grooves).
Is this typical?
At least I know why it shoots terrible with regular 6.5mm bullets.
I plan to try some 0.268 diameter 160gr Hornady bullets to see if it shoots any better.

[riceone]

Tonight I got an email from a friend that had a T38 barrel that was so worn the 264 bullets tumbled on the way to the target. He switched to Hornady .268 bullets and the same rifle shoots in the black. Word of caution - start out with light loads on the .268 bullet. The same guy was using the .268 bullet in a badly worn Carcano and it was locking the bolt. riceone.
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Most people who preach tolerance are very intolerate.

[Smokey]

I forgot to mention, the barrel has SIX lands and grooves, not four! Is this at all common?

[gwsiii]

I think there is official documentation that the Japanese began phasing out the 6 groove bores around 1918, unfortunately, not completely so they pop up occasionally after that. Frank has a pretty specific serial range though. I'll see what he says. Trey
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I didn't pay to much for that old Arisaka, I just bought it a little bit too soon!

[Smokey]

I suspect the "oversize" bore is the result of gas bypassing the bullet in the grooves. Gas erosion in that case will increase the groove diameter, while the lands stay relatively constant. I got a batch of 160gr 0.268 bullets. Tried one each over 32.5gr IMR4320, 35gr WW760 and 38gr IMR4831. No pressure signs with any of them. I loaded a batch with the IMR4831, I'll try them at the range for accuracy.

[Smokey]

T-38 with 160gr 0.268 bullets:
I loaded them over 38gr IMR4831. They gave about a 4 inch group at 100 yards, about 16 inches high. Looking at the primers, pressure was well below maximum. This is a huge improvement since the rifle didn't even stay within a 3-foot group with 0.264 bullets before.

[gwsiii]

Thanks for the update, from what I've read, (...updated, this is for the Type 99 Rifle) rear sight down setting is 100 meter, rear sight flipped up with slide up off of base setting, the notch is for 200 meters, with sight flipped up, and slide down to base setting 300 meters. I don't shoot enough to know how the difference in meters and yards (3"+ per yard/meter difference) would work out on the final impact on the target, but I have seen a training sight picture for Italian rifles with the blade of the front sight set at the bottom of the 'V' with point of impact in the 'V' opening resting on top of the blade sort of like this:
. Trey
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I didn't pay to much for that old Arisaka, I just bought it a little bit too soon!

[Smokey]

This T-38 apparently is set for 300 yards with the rear sight set down.
Standing the sight up, the lowest setting is 400 yards.

[gwsiii]

I checked my notes and the above is from a translation of the 99 rifle manual, so I'll go back and 'fix' it. I've got to see what I have on the 38, Frank may have a translation of the manual. Sorry for the confusion. Trey
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[Smokey]

What are the bore dimensions for a Type-38 barrel in good condition?
I'm considering getting a replacement barrel from SARCO for my other T-38 but need to be able to verify it's condition.

[Francis C. Allan]

My notes for the T-38 book covering rifling indicate that the groove diameter maximum is .267 inches (6.78mm). Keep in mind that the rifling is of th epolygonal (Metford) type.

The "battele sight" (ladder folded down) is indeed set for 300 meters and the lowest setting on the ladder is 400 meters, but it requires the slide to be raised to use ithe ladder's V-notch.

I did not note where the groove diameter came from but I have seen it is several publications.

I hope that this helps the discussion.

Frank
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Francis C. Allan
20Courtney Place
Palm Coast, FL 32137

(386) 445-4225

[Smokey]

Frank,
Thanks for the info on groove diameter. I guess I'll just stay with the 0.268 Hornady bullets and the original barrel. I expect I can tighten up the group size (to something smaller than 4" at 100 yd) by playing with the powder charge.

[Smokey]

What was the bullet diameter for the Japanese military ammo?

[Francis C. Allan]

The Type 30 round (Cupro-Nickel, FMJ, RN) had a diameter of 6.7mm +/- .3 in some examples I measured some years ago; bullet length was 33.2mm and a weight of 161.5 grains +/- .2 grains.

The Type 38 Modified/Reduced Charage round (Cupro-Nickel or Gilded- Metal, FMJ, Pointed) in a fairly large group that were recovered from the Aleutian Islands that I measured, had average diameters of 6.7mm +/- .2mm; bullet length was 32.2mm, and a bullet weight of 138 grains (+/- .5 gr.).

The original Type 38 cartridge (without the thickened forward wall in the front only) had a bullet weight of 139 grains (+/- .3 gr.), but this is based upon a very small sample.

I hope that this helps to answer your question.

Frank
_________________
Francis C. Allan
20Courtney Place
Palm Coast, FL 32137

(386) 445-4225

[Smokey]

Francis, really appreciate the info. 6.7mm works out to be 0.264 inch.
I wonder what makes the bore become so oversize that 0.271 bullets become the proper fit all the way out to the muzzle?
Typically erosion makes the rifiling disappear near the chamber, but the bore is less affected as you go towards the muzzle.