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

[arado]

I inspected my Chinese 6.5 Arisaka cartridges. This is the findings. OAL 3.006" weight, 324grains. base diameter .451". bullet weight, 136.6 grains. bullet diameter, .262". Powder type, flake. charge 28.9 grains. Case weight, 155.8 gr. checked 5 rounds. Very consistent. gary.

[ireload2]

It has been a while since I looked at this thread. I remembered that the current CIP standards have this round listed - not that I have a lot of faith in CIP matching the real world for this round.
The area of the bore is given as 33.69 mm squared which by my calculations gives a radius of 6.5495mm = .25785 inches.
The CIP drawing is lousy as usual so it is not clear what dim is the land dia but it appears to be 6.33 mm =.2492 and the bullet is given as .261.

[jmoore]

it is not clear what dim is the land dia but it appears to be 6.33 mm =.2492 and the bullet is given as .261.

Which would make the usual .264" bullet a very tight squeeze! Haven't focused on these rifles in a while, but I think my next step is to pull some military bullets and load them in some once fired cases. Probably ought to spend a few hours trying to zero the scope in some more, but having those tiny grub screws out at the range is more than a little scary. Might try the optical bore sighter instead, but I tend to reverse the corrections, and it has a 4 MOA grid (which isn't all that easy to read with the low powered scope.)

[Patrick Chadwick]

CIP dimensions:

Land diameter 6.33 mm
Groove ,, 6.63 mm
Groove width 3.50 mm - which, if correct, only leaves about 1.6 mm for each of the 4 lands.


Cartridge base (max) 11.45 mm
Chamber width at base (Mini) 11.48 mm

The basic form of Metford rifing is outward-bulging segments opposite the lands. This rifling was invented by Metford in the days of BP shooting with lead bullets, and the form means that if you imagine a line crossing through the center of the barrel, and rotate this, the lead is alternately shifted left and right of the center axis, rather than being cut by the edges of any grooves. With the Lee-Metfords, the rifles showed excessive bore wear with smokeless powder, but this must have had something to do with the propellant, as the rifling worked OK for the Japanese for a long time.

The dimensions above should, I think, be understood as the "inner circle" and "outer circles" of this shifting line, and the average is therefore something close to the mean of these two values, i.e. 6.48 mm. However, the outer (curved) segments are wider than the inner (land) segments, in the ratio of 3.5 to 1.6 mm. So if you made an exact calculation, I expect it would come out near enough to 6.50 mm for our purposes.

[ireload2]

I have one of these barrels that is partly ruined. I should get it on a mill and cut away half fo the bore.

[Patrick Chadwick]

I have one of these barrels that is partly ruined.

Are you sure? A perfectly good Metford profile can be mistaken for a conventional "square-edge" profile that is badly worn. Driving a slug right through the well-lubricated bore from the chamber to the muzzle is the best test. If the slug stays tight all the way, and does not suddenly fall free (indicating bell-mouthing, bad wear or bulging) the bore is usable.

[ireload2]

Patrick,
We have a wasp in the US called the mud dauber that loves to build its mud nest in holes of any sort. In this case someone had shortened the barrel to sported length and left it exposed to the mud daubers. It has huge rust craters about midway between muzzle and chamber. The bore between the mud and the chamber is like new.