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

[Patrick Chadwick]

My CIP-derived information gives bore 6.33 mm = 0.249" and "groove" diameter 6.63mm = 0.261. Twist is given as 200 mm = 8"

But since the Norma cases I have appear to be CIP-compliant, but are clearly too small for the chamber, I would not trust these specs overmuch!

Patrick

Information

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[vintage hunter]

Ok, have the book. Specs for type 30 and type 38 rifles and carbines: Bore diameter-.256''. Groove diameter-.262''-.269''** Twist rate:** 1-7.88''(early) to 1-9''(late). Number of grooves: 6(early) or 4(late) Cartridge specs, 6.5mm, type 38: O.A.L.-3.00'' bullet dia.:.262'' Weight: 139gr, Length: 1.28'' Powder type: Nitrocellulose, Charge: Approx. 33gr, MV: 2400 fps, Pressure: 38,000 psi, Case lenght: 2.00'' oal, Length of shoulder: 1.53'', Dia. at rim:.4761'', Dia. at neck: .291'' Length head to shoulder: .20'', Length of neck: .27'', Diameter at base: .449'', Diameter at shoulder: .414''. ** Notes...Groove depths and rates of twist have varied considerably with time and place of manufacture** JMHO but the variation in groove depth/diameter without an increase in bullet diameter is the likely cause of some rifles lacking in the accuracy department. Regarding Norma brass, is it truely undersized or were the rifles specs not adhered to during manufacture?? Do they stretch? Don't think so, never had a head seperation with Norma but I have with Graf/Hornady brass. (not PRVI/HORNADY)

[Patrick Chadwick]

Regarding Norma brass, is it truely undersized or were the rifles specs not adhered to during manufacture??

As I have already mentioned, it seems from my measurements that Norma = CIP but CIP not= real-world Arisaka.

And as for some other types, most noticeably the Carl Gustav (Swedish Mauser), the rifles were made first, and CIP (or SAAMI) came later. I have a suspicion that the people who derived the specs took original values and then knocked off a not inconsiderable margin to be on the "safe" side. With the result that in the modern world, where every manufacturer lives in fear of liability claims, the manufacturers take the spec values, knock off another margin to cover worst-case manufacturing tolerances, and so we end up with noticeably undersized cases!

Patrick


---------- Post added at 11:01 PM ---------- Previous post was at 10:57 PM ----------

Twist rate:** 1-7.88''(early)

This wierd value is, of course, nothing other than 200 mm converted to inches (rounded up)

[riceone]

I've been sorting through my amm in the last day or so and I found 40 or so rounds of 6.5x50 ammo that was loaded in cases made from 7.62 x 51 Nato brass. When I made this brass I used a swadge die (that I made) and recuced the base of the case down to .456" (if my memory is right) and then run the cases through and old Herter full lenth die doing it in steps till the bolt closed on the case with no resistance. This produced a case that did not swell at the base and it fit the chamber so there was no stretching later. This is the only way I know to have a case that fits the chamber as it should. I was making and selling the swadge die and I think there is someone on this board that has a copy. With the variance in Japanese chambers you are going to have to fit each rifle seperately IF you want a perfect fit.

[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