Twist Rate on Japanese Arisaka Type 38 6.5x50
I've been trying to find the twist rate of a Type 38 Japanese Arisaka.
It is a 6.5x50mm rifle I had re chambered for 6.5x55mm Swedish.
I know I can probably do the old cleaning rod/count the turns trick, but I typically get erroneous results. Does anyone actually have documented data?
How do you figure
Originally Posted by rattletrap1970
You get erroneous results? An inch is an inch and a trun is a turn. Often twist rates in barrels are not precise. That is to say they were not made with exact twist rates in the beginning.
Do a series of measurements and average them is you don't trust your repeatability but the simple measure the length on one turn will tell you the ball park you are in.
Bores of the Jap 6.5 apparently do vary greatly in diameter. I've seen information on these that some had bores closer to .270 than 6.5, but these may have been rebarreled in China using the Chinese 6.8 barrel blanks left over from the aborted attempt by the Chinese to produce a distinctively Chinese infantry cartridge.
Probably best to give measuring your bores twist and diameter a try, published information may or may not help with individual rifles.
Similar situations arise when studying the Enfield barrel types, Early production savage No.4 barrels were rifled on machinery set up to produce barrels for France, and these have a twist a bit faster than that specified for the Enfield. Enfield bores can be found with two grooves, three grooves (very rare) four or five grooves and even Six grooves from Savage.
If your rifle has the barrel it left the factory with it still may not match the published specs.
Yes, erroneous results. It happens when the tight patch you are running down the barrel slides instead of gripping the rifling, due in part by the bearings in the cleaning rod handle sucking.
Anyway, I have found (through no small amount of effort) that it is 1 in 8.375. So.. I guess I'm all set.
Seems like mine was close to that, though what I have is a Type 44 instead of a T-38. I'd never heard anything about variation in bore diameter among Arisaka rifles, but oversize chambers were quite common. But that was to keep the reamers in production longer, as they got smaller with each sharpening.
The Arisaka in 7.7 is supposed to have Metford patern rifling, but every last ditch 7.7 I've examined so far has had rifling more like that of the 93 Mauser, flat bottomed grooves and slightly rounded lands.
Originally Posted by Vibe
No telling what sorts of substitutions were made during wartime.
Did the Japs use gain twist? Seems like I read that in a reference somewhere.
Regarding gain twist -
I believe that you're thinking of a Carcano.
twist rate for type 38 6.5
My old Sierra manual said 1 /9 twist . standard jap carbine.
There are Italian manufactured Carcano rifles in 6.5 Jap, called the Type I (I standing for Italian) these use a mauser type staggered row magazine and Japanese style dovetailed stock.
Originally Posted by davejones
I believe these are rifled according to Japanese specs rather than using the Italian 6.5 bore (.268) and don't have progressive twist like the early carcano.
Later Carcano rifles used a non gain twist as well.
I've read that the Type I is the most accurate Japanese issued rifle, but few were used in combat, many were found still warehoused at the end of the war, probably due to lack of replacement parts or armorers trained in working on non Japanese designs.
National pride has been given as a reason, but I sort of doubt that.
Thinking on what I'd read about oversized Jap 6.5 bores best I can remember the examples cited were calvary carbines used in China. Not sure what model these may have been, possibly WW1 era rifles, perhaps something along the lines of the type 30.
In sources on Jap trainers they mention some fully functional rifles originally relegated to trainer use which were later issued for use in China when arms became in short supply.
There are some oddbal rifles built on a rare rejected action design that been shelved in favor of the 38 and 99 rifles, I think it was the Type 35 rifle, an improvement over the type 30 but with problems of its own which made the Type 38 a better choice. I think the rebuilt 35 was called a Type 45 and very few were made.
Many Jap rifles were rebored or rebarreled and otherwise altered by the Chinese and other once occupied nations. Chinese Arisakas can be found in 8mm and 7.62X39 and there are full military .30/06 conversions from some other country besides the conversions done by American owners. Mexico bought Arisakas in 7mm Mauser caliber.
It pays to be certain before trying Jap ammo since the rifles may no longer be in the original caliber.
I have a few clips of Jap 6.5 ammo and the bullets all measure .260" diameter. I thought they'd be .264".