Type 38 pressure issue

[HIGHRPM]

I need some help. I finally got around to reloading some light rounds for my type 38 carbine and went to the range. While the gun shot very well and printed on paper instantly, when I took the rounds out to inspect I found the case had really stretched out just above the head which I likened to a military loose chamber, but the primer flattened and looked like it was trying to push out. I tried two different powder charges and got the same results on both and they were the lightest charges, so I dare not shoot the other rounds. Since I find that nobody makes a headspace gauge for this caliper, what does a guy do ? The gun shops in my area are retailers not gunsmiths so they are useless. Do I buy and try different bolts, reload even lighter rounds ? I have never had this so I am not sure which way to go, so again, I need some help !

Information

Warning: This is a relatively older thread This discussion is older than 360 days. Some information contained in it may no longer be current.

[vintage hunter]

Case swelling is normal with Arisaka's so unless you start experiencing case head seperations don't worry about it. Protruding primers can be a sign of haedspace issues but in this case the light loads are,IMO, the likely cause of it. Headspace gages are available from PPG in White City, Oregan. Ph. 541-826-5808 Ask for David Kiff.

[Patrick Chadwick]

I've been there and done that!

I, too, have an Arisaka T38. And when I first tried it out with some ferociously expensive Norma ammo the cases and primers looked just like yours.

Don't panic!
Don't go crazy looking for a headspace gauge!

Stay calm and read what follows right through before switching off in disgust, as I may be about to tread on a few toes. For which I apologize in advance, but it is all my considered opinion, based on not inconsiderable experience.

First, dear brethren across the pond, I have a couple of secrets to impart.
Many of our beloved old service rifles were designed and manufactured long before WWI. Long before CIP and SAAMI were thought up. The published specifications for several chamberings were, I suspect, derived long after said rifles were produced. A case of being wise after the event, but of course intended to provide help for commercial manufacturers. No imperial Japanese/Russian/British arsenal would have cared a hoot about international standards bodies.

Another secret: rifles, when you remove the military aura, are machines. Machines subjected to heavy loading and thus wear. So those chambers, which were never built according to CIP anyway, are now even bigger than when they were new. And when they were new, they were often built generously, so that the average Poilu or Tommy could drop his rounds in the mud, pick them up, wipe them on his grubby battledress, stick them in the chamber - and the rifle would still function properly. If you take some time to study the history of the Ross rifle, you will find that its lack of “muck tolerance” was a major cause of its failure on the battlefield – although it acquired a good reputation as a target rifle.

So “real world” imperial rifles were designed primarily to work reliably in conditions that would make a collector cringe. It is illuminating to read the descriptions of the trials that lead to the selection of the Martin-Henry as the British standard rifle in the 1860s, which involved soaking the rifles, burying them for weeks in the mud, digging them up, scraping out the muck, and firing them again. What passed such tests was a tough design - the M-H. Maybe not the target-shooter’s choice, or a watchmaker's showpiece. But very, very tough.

And, of course, it was not a typical military objective to reload cartridge cases. Except. of course, in the special case of Lettow-Vorbeck’s askaris in Tanganika. But that is another story…

Returning to our mutual problem: The T38 (I cannot speak for all, just mine, and maybe yours) has a chamber that is, particularly on a worn example, so much longer than the CIP figure, that when you load a case that has been fully sized to CIP specification the following occurs:

Note—I am indebted to jmoore for the first comprehensible description I ever read of this complex chain of events. Jmoore, if you are reading this, please chip in as I know you have done a lot of “T38”-thinking.

When the rifle is fired, the firing pin pushes the cartridge as far forwards as it can. If you remove the extractor, this could be so far forwards until the shoulder stops in the chamber that the firing pin is unable to detonate the primer. However, in most cases the extractor will hold the case well enough for the pin to detonate the primer. In your case, it looks as if the firing pin only just managed to cause detonation.

The case expands, and being thinner at the neck end, will grip the wall of the chamber there and start to push the rest of the case backwards, stretching it in the process. While this happens, the already ignited primer is pushed back out of the primer pocket much faster than the base of the case can move - the primer backs out and is forced flat onto the bolt face. The pressure causes the backed out portion of the primer cup to expand.

Now the base moves back as the case stretches. The primer cup, now slightly oversized, has the cartridge base forced down around it, flattening the cup, and this causes the cup to appear as in your photos.

I also had this effect, and thought "OMG, hazardous overpressure!" Not so, the cause is the enormous end play created by a modern cartridge made to CIP or SAAMI dimensions being fired in a chamber that is considerably longer to the shoulder. And the answer to this problem is to get the case to stretch at the neck and not at the base.
One solution has been thought out and described by jmoore, so at this point I defer to him. (You should be able to find it on this forum).

Since I already had a stock of the Norma ammo, I tried another solution. I simply used a bullet puller to pull the bullets out so far that when the cartridges were loaded the bullets touched the lands. When fired, the primers looked somewhat healthier, but still doubtful - probably because the neck tension was weakened by the partial pulling of the bullets.

So my next test will involve pulling the bullet completely, resizing the neck, and seating the bullet almost on the lands again, but with a slight crimp. I will report back when I have tried this out. In the meantime, the jmoore solution is best.


Patrick

[HIGHRPM]

Thank you very much for the info, it all makes real good sence. This situation caught me off gaurd as all of my other milsurps run smoothly. I understand that the action is rated to have been very strong, it just confused me when I fired off light loads to test and saw the case and primer issue. So I will reload these rounds, with a hotter load and stretch out my col to see if I can get the case to stretch differently. And we will see what happens. And Patrick, I don't think you stepped on any toes, experience speaks loudly in my mind, thanks.

[vintage hunter]

The only set headspace gages I've ever owned just happen to be 6.5 Japanese. The reason I own them is because I once built up a sporter on a T 38 action with a commercial barrel in the original chambering to get away from the case bulging issues, among others. I'd often heard the gages were built to SAAMI/CIP spec and the rifles not story and pretty much went along with it until I happened to try the gages in my one all matching T38 carbine. No surprise when it closed on the GO gage but big surprise when it would'nt close on the NO-GO gage. To make a long story short I have 4 T38's that will close on the GO but not the NO-GO. What do you make of that Patrick ?

[jmoore]

Patrick's post covers the situation rather better than my usual short answers! But one other thing to consider: Like P14s and M1917s, the locking lugs are of "interrupted thread" form, i.e. they are on a slight angle- Usually! (Whole different subject there.) So if there is any bolt lift during the striker fall, the breech face may be backed off a few more thousandths. Also plays tricks on many folk who love to obsess over headspace. As long as there's no case head separations (annoying but not very dangerous- except in combat!) I'm more concerned if there is enough room to properly chamber a round without mechanical binding or possible crushing the case mouth tight against the bullet driving up pressures to insane levels. Too short headspace is potentially more dangerous than too much! But fortunately very rare in military arms.

[Patrick Chadwick]

To make a long story short I have 4 T38's that will close on the GO but not the NO-GO. What do you make of that Patrick ?

The oversize (by comparison with CIP/SAAMI) chambers on T38s have certainly come up several times on this forum. So maybe you have a statistical freak? Maybe there were differences from arsenal to arsenal or batch to batch. Are those T38s all from the same series?

[jmoore]

Here's a thread for reference. Click on link below:

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

Note that the first Post has an additional link.

Maybe that mess will clear up some questions, but it's a work in progress. VERY slow progress! Too much going on to get much range time lately.

Note in Post #3 that the Norma rims were about 0.010" thinner (and case shoulders similarly short from a later post) than the others. Instant increase in headspace, with the attendant extra case abuse and primer dramas.

[HIGHRPM]

WOW !!! Talk about great work on the T38 ammo. Jmoore, thanks for all the previous work you have done, trying to figure out the ammo for this rifle. A lot more complex than I imagined. I am going to try and fireform some cases and up my powder charge to eliminate the light load issue. Now a question, I have a good supply of reloader,15,17,19,22 and IRC 4350, 4895. What would be a good powder to use to fireform and how much of a charge ? Would you recommend the cow method , or ??? Again, thanks for your time and efforts, I have learned a bunch !

[vintage hunter]

Patrick, I have 1 carbine made at Tokyo Arsenal around 1910, 1 Kokura rifle made about 1934, and 2 Kokura carbines from the same series. Will have to look and see what series the series is on those. The Grafs brass has thin rims also but I'll have to measure it again to see just how much. Have'nt played with Arisaka's larely and this stuff has faded from memory. Another note on the Grafs brass, the only time I've ever experienced case head seperation was with handloads that utilized it.