Type 99 Arisaka challenge.

[Mauser fan]

I bought a complete bolt this past weekend for one of my type 99 Arisaka receivers and it fits well. Then I re-installed the original barrel back onto the receiver and checked the headspace and it is .051 inches over the max.I also slugged the barrel and it is a rock solid .312 with sharp rifling and the barrel is Crome lined. It would be a shame to scrap it.
I have a set of RCBS 7.7 Jap dies and have made 20 cases from 30-06 cases all chamber just fine just too much headspace. So I have barrel issue. I know that the 7.7 chambering was designed to be sloppy and be fired with a relatively dirty chamber. But .051 over?
The trim to length for the 7.7 case is 2.270 inches, max case length is 2.280 inches. The chamber measurement is 2.331 inches which is .051 over the max. A 30-06 case has a maximum overall length of 2.494 inches.
So as far as I can tell I have 2 options. Set the barrel back or re-chamber it to a different cartridge. Setting it back has a very unique set of challenges mainly dealing with the channel cut for the extractor. Not impossible but a great deal more work to do so.
I have read that 7.7 Arisaka's were re-chambered for use with 30-06 in the original barrels during the Korean war by the US govt. for the South Korean Army. It seems to be a simple straight forward task to do so.All that I would need to get is the reamers a rougher and finisher and I would have to change the de-capping pin in a sizing 30-06 die from a .308 to a .312 de-capping pin.
Has anyone else done this?

 

[Blue68f100]

The decapping pins should all be the same in the sizing dies. has nothing to do with the bore size. You should have been setting your sizing die to match your chamber specs, long as it is. Provided your not expanding the base.

I would cut the barrel back if it was me. Determine your thread pitch. you will have to use that in increments to index the barrel. If the barrel screws directly to the receiver allow for torque, normally around 0.001"-0.0015".

If your going to rechamber, it's already roughed out, a finish reamer should be all you need.

 

[Mauser fan]

I have time to think about how to best approach this project and I'm in no hurry to get it done. This is definitely making me use my brain and keeping me busy. Since I have 2 receivers and barrels and 1 bolt only that matches up to 1 barreled action I have to be conscientious not to make any mistakes otherwise I'm scraping the whole project. This is definitely challenging.

The thought behind all of this is to bring some of these old Milsurps back to life even if they aren't # matching original. I have a couple of direct sources for parts and actions. What is troubling about these sources is that they are parting out complete rifles to sell the parts because it is more profitable for them to do so. That is why one of the sources has so many barrels actions and nothing else left.

 

[Mauser fan]

I have done my homework and I have concluded that my best approach to this project is to just re-chamber it to 30-06. A 7.7-06 for all intents and purposes. I'll just buy a finish reamer with some headspace gauges and get to work.

 

[Mauser fan]

Here is the project in its infancy.

 

[PapaG]

Thousands were converted to 30-06 commercially during the fifties and sixties. Ads run in the back of F&S, OL, and Sports Afield stated, "Japs, convert your 7.7 to 30-06, 6.5 to .257 or something like that." Slightly larger cartridge base on the 7.7 but I've been told, very emphatically by keyboard commandos, that is isn't "that much".
Go for it. It is a terribly strong action according to Ackley and others.

 

[Jim Watson]

I have read that Arisakas were rechambered to .30-06 as secondary standard for ROK.
Likewise there have been 7.65 Mausers rechambered that way.

Of course a handloader can use .312" bullets and have a .31-06.

 

[Jerry M]

What kind of accuracy would you expect from a .308 projectile (from a 30-06) tired down a.312 inch bore? My vote is it would suck.

 

[Mauser fan]

I have read that Arisakas were rechambered to .30-06 as secondary standard for ROK.
Likewise there have been 7.65 Mausers rechambered that way.

Of course a handloader can use .312" bullets and have a .31-06.

I am a hand loader and plan on doing exactly that.

 

[Slamfire]

Seem to have created a double post

 

[Slamfire]

I am a hand loader and plan on doing exactly that.

Let me say that "headspace" is not as safety critical as cartridge case protrusion and case head support. Our in print experts only understand headspace to the extent that they can sell reloading equipment. It surprised me just how few of them understand anything about cartridge case head protrusion. Even Hatcher understood headspace only from a reloading perspective, based on his lack of discussion on it, he did not appreciate the criticality of supporting the cartridge case head by steel. The cartridge is a gas seal, it is not strong at 50,000 psia pressures, and if it is not supported, it will rupture.

To understand what I am talking about, read the blowback section in Chinn's Machine Gun book.

Chinn’s series at Hyper books:

Volume IV, Design Analysis of Automatic Firing Mechanism, by LTC George Chinn.

http://www.ibiblio.org/hyperwar/USN/ref/MG/

https://www.ibiblio.org/hyperwar/USN/ref/MG/IV/MG-V4.pdf

Read chapter 1 on Blowback in Vol IV. This picture came from that section, it is a 20mm case.



The thing is, headspace is important for reliable ignition, that shoulder needs to rest on something hard or the primer won't be struck hard, or struck at all. A large bolt face to chamber shoulder issue can easily be fixed as long as the cartridge case head protrusion is OK. I don't know how it is set, but generally the numbers I have seen are around 0.10 to 0.110 inches. It seems to me designers are trying to keep the top of the primer pocket inside the chamber. Someone with a finite element model could run sensitivity measurements and find out just when the sidewall ruptures. I am not sure how they did it in the sliderule days.




Chamber headspace is easy to measure, and generally if the headspace is off on a factory rifle, the lugs have set back or the receiver seats have set back. Why this is important, is because if too much of the case head sticks out of the chamber, the case sidewall will rupture.

I have seen in an old NRA book how a gunsmith determined the case head protrusion was correct. The smith removed the barrel, measured distances from the receiver ring face to the bolt face, and them measured the shank, did some more measurements and figured out how much of the case head was sticking out of the chamber. It took a lot of work and thinking about which measurements to take.

If the cartridge case protrusion is safe, then simply lube your 7.7 cases and fire them. Greasing the cases will prevent the case from gripping the chamber walls, the case will slide back to the bolt face, the shoulders will fold out in the chamber. And after firing you will have a stress free, perfectly fireformed case. Make sure the shoulder and side walls are lubed. Sizing lube works great, I have used automotive greases, Johnson paste wax, and hair gel. Hair gel is non toxic, unlike industrial greases, and has a pleasing smell. After fireforming, bump the shoulder about 0.003" when you reload, and shoot some more. I regularly fireform greased cases,





300 H&H new cases being fireformed






This is the Oerlikon 20mm cannon mechanism. It was an advanced primer ignition system, and it was retarded/delayed blowback action. The mechanism was never locked. As you can see, the case moved a long ways before chamber pressure dropped enough that the sidewall would not rupture. This mechanism used greased cases in WW2, then oilers were added after the war. Grease is a mess, gets all over everything, floats in the air, smells awful when it is burnt. Grease attracts dirt, which will score a chamber. And the stuff has to be pre greased, and it was. You can understand the military wanted to get the grease out. But the fact of the matter is, as long as that case head is enclosed by steel, the whole case can be moved inches, as long as the case does not grip the chamber.



This Nambu light machine gun used an oiler. That cap on the right is on top of the oil tank





I think it is in Chinn, but pre WW2 machining technology was not repeatable enough to produce perfectly toleranced replacement machine gun barrels. So headspace variance was large enough, that case separations would happen, jamming the gun. So there were machine guns with oilers on top, not because the mechanism needed it to due case friction, but because without a lubricated case, cases would separate in the chamber if the headspace was too much.

There were mechanisms that needed case lubrication



Since the Arisaka has a claw extractor, the case will be held close to the bolt face (most of the time) regardless of the clearance of case shoulder to chamber shoulder. For the "not most of the time" situations you want the shoulder within 0.003" of the chamber shoulder. I have had case rims slip off Mauser type extractors.

By the way, military M14's have huge headspace dimensions. A gunsmith bud of mine was requested by some buds deploying to Iraq to mechanically check out their issue M14's. These were M14's that were either new, or rebuilt to Government spec. Bud said the things swallowed his field gauges. They still went bang in the theater and feed and extracted. The units had these M14's to shoot mines. Cartridge case head protrusion was OK though or they would have gone kaboom!

 

[Mauser fan]

By the way, military M14's have huge headspace dimensions. A gunsmith bud of mine was requested by some buds deploying to Iraq to mechanically check out their issue M14's. These were M14's that were either new, or rebuilt to Government spec. Bud said the things swallowed his field gauges. They still went bang in the theater and feed and extracted. The units had these M14's to shoot mines. Cartridge case head protrusion was OK though or they would have gone kaboom!

When I was in charge of a group of small arms repairers before and while deployed to Iraq it was and still is common practice to inspect all of the small arms for case head protrusion, firing pin protrusion, throat erosion and head space etc... That is a direct support function. The units that I and my troops supported had whole host of different weapon systems to provide maintenance for. From pistols, rifles, shotguns, grenade launchers, machine guns and some foreign weapons AK's etc... This included the famous M14 and M1As. Our maintenance support wasn't just limited to small arms it included artillery and tanks.

We had the same experience that your friend was describing to you that he had with the M14's when they were fielded to our units for various roles.

Our biggest head aches were more often than not the operators of the Ma Deuce. Too often they would not install the barrel in correctly therefore creating a headspace and timing issue. At the very least there would be a ruptured cartridge if they were able together it to fire and not have shrapnel from the case in one of their extremities. Hell I still have a set of gauges and a ruptured cartridge extractor. Here is a picture of them on my bench.


Let me get back on topic here and say thanks for sharing the links with us all. I will read them later on this week in more depth.

Jeremy Mclean
SFC US ARMY Retired

 

[Jim Watson]

And the next time you make some 7.7 out of .30, just set the die so they will just chamber freely.

Less work than rechambering.

 

[Mauser fan]

Precisely.

 

[PapaG]

What kind of accuracy would you expect from a .308 projectile (from a 30-06) tired down a.312 inch bore? My vote is it would suck.

It sucked when I did it. Shotgun patterns of keyholed bullets.
Found a box of .312 dia bullets and presto, 3 moa with issue sights.

 

[Slamfire]

When I was in charge of a group of small arms repairers before and while deployed to Iraq it was and still is common practice to inspect all of the small arms for case head protrusion, firing pin protrusion, throat erosion and head space etc... That is a direct support function. The units that I and my troops supported had whole host of different weapon systems to provide maintenance for. From pistols, rifles, shotguns, grenade launchers, machine guns and some foreign weapons AK's etc... This included the famous M14 and M1As. Our maintenance support wasn't just limited to small arms it included artillery and tanks.

We had the same experience that your friend was describing to you that he had with the M14's when they were fielded to our units for various roles.

Very interesting!

Let me add another comment, it is better to keep a military rifle in its original cartridge for function reliability. The cartridge timing, that is when it rises from the magazine, and when it releases, was carefully examined and the feed lips machined accordingly. Bingo for the follower. Change cartridge length, cartridge OAL, cartridge diameter, even bullet diameter, and the feed system may puke. I have seen this with pre 64 M70's. A NM pre 64 M70 in the 30-06 did not feed 308 Win reliably till I purchased all the short magazine conversion parts. A USFA 243 Win did not feed reliably when converted to 308 Win. I have no idea how a short Arisaka action will feed and extract with a longer cartridge. I don't know how you get a 30-06 in the magazine. I could not feed 30-06 rounds into the magazine of my 7.7 Arisaka, the magazine was too short.

There are those who convert old Mauser actions to belted magnums, and they sure have difficultly getting the things to feed reliably.

This is also true for semi autos. A shooting bud was running a 6.5 Grendel in his AR15. He spent a lot of time trying to get those Grendel magazines to feed reliably. Look at all the fun the 450 Bushmaster guys are going through, trying to run 450 Bushmaster rounds in the AR15 action.




I was told five rounds are the magic number for a 450 Bushmaster magazines. They won't function reliably with more rounds.


So, unless you want to experience new forms of malfunctions and chase novel approaches to fixing them, stick with the original cartridge in a military rifle. And I am going to say, there is nothing wrong with the ballistics of a 7.7 Arisaka round.

I believe had the 50 caliber guys been oiling their ammunition, I believe they would not have been experiencing case separations due to over length chambers. The case would have simply slide to the bolt face and the shoulders folded out to the front. Instead, when the front of the case adheres to the chamber, and the middle has to stretch, because there is clearance between the base and bolt face, at some level of stretch, something has to give.

 

[Mauser fan]

I have just about everything I need to make a usable rifle again. I still need the magazine spring, follower and the trigger guard screws. Once I have the entire action together I can make a better determination to the best approach and make the old girl go bang again. Either way she will be a scoped sporter when I'm done.

I haven't pulled the trigger to buy a 30-06 finish reamer yet. I'm still floating the idea to keep it chambered in 7.7x58mm. We'll see what happens. Stay tuned.