Headspacing with spent primers ...

It's not uncommon for mil surps to swallow no go gauges, hence the field gauge to evaluate if or when to set back the barrel or re-barrel.
The primer thing sounds sketchy to me, the cartridge being the wildcard.
I also wonder about the resolution of a depth gauge, especially if it's the male end of a caliper.

If like a 30-30 that headspaces on the rim, the primer method may be of use.

But it looks like the 7.7 headspaces on the shoulder. A head to datum measurement. Brass that is new, would not be a good test, using the primer method.

What if the extractor is stopping the new brass from fully entering the chamber?

243winxb said:

But it looks like the 7.7 headspaces on the shoulder. A head to datum measurement. Brass that is new, would not be a good test, using the primer method.

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^^^^ What 243winxb said. There's no way to accurately measure headspace of a cartridge that headspaces on the shoulder without a headspace gauge. You could use shims cut from shim stock or feeler gauges in conjunction with a No Go gauge.

243winxb said:

What if the extractor is stopping the new brass from fully entering the chamber?

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I always remove the extractor and spring loaded ejectors when checking headspace. Fixed ejectors can stay in place.

I cannot see how I would get any better data with gauges.

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Let's see - you don't know what is the actual safe headspace tolerance for 7.7×58mm chambers, you don't know what are the actual headspace specific measurements of the cases you are using -there is no way you could accurately measure head to datum point distance, you are using SAAMI data for a different cartridge... So yea, sure, no need for gauges...

A lot of cartridges head space from a datum on the shoulder. Not sure about the 7.7 jap.
If you were using a cartridge that was fired in the chamber of the rifle in question and if it fit a case gauge, "in a pinch"........................maybe.

M100C said:

I know the case shoulder is touching, and I know with the bolt closed, the primer is seated to within 0.005" flush to the case head.

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With the shoulder touching, i say, load and shoot them. Good Luck.

Just because you don't know something does not make it insignificant, or non-existent... Have fun and safe shooting.

Edit:
M100C, you were talking about headspace, so I commented on it and your method of measuring it. Headspace is a known dimension, that has a min and max allowable tolerance. With your method you are only measuring the difference between the case length (unknown) and chamber length (unknown). That's it. Nothing more, this measurement is not "headspace". A field gauge has the maximum allowable (for whatever reason) dimension for a said cartridge - maximum headspace. So, a field gauge tells you if you are bellow that dimension, or exceeding it. Said gauge may not give you the exact numbers up to thousand of an inch, but it gives you a known reference point. Something that an unmeasured brass case cannot give you. I hope I made myself clear.

BTW, I suppose that with .005 difference the rifle will shoot just fine...

http://stevespages.com/page8d.htm Make sure this is the correct one. I think there is another one that very close to this one. ??? And another one.

A skilled reloader using knowledge, reference material, the right tools, a large measure of common sense, and a larger measure of caution can do things that the books will tell you not to do. The trick is knowing if you are that person. Only you can know that.

M100C said:

I will load down with H4895

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To light and the head to datum measurement will become shorter. Case body expands outward, pulling shoulder back. Trim length will also get shorter.

Spent primers work just fine for any cartridge type, if you 1) use a comparator bushing to record the length of the test case and that of your resized cases, 2) have cases shorter than the chamber, and 3) remove the extractor (and ejector for plunger types) from your bolt. I've used the same spent primer method in the past. Item 1 ensures accuracy in the process. Item 2 here is kind of a "gimme," since the bolt has to be able to close. Item 3 is a requirement for any and all headspace checks, whether you use a gauge set or not, to prevent false reads based on extractor or ejector interference.

All we're really trying to do is determine the fit of factory or reloaded ammunition between the boltface to the datum line of the chamber shoulder. Knowing the actual length isn't critical, so reference points work just fine (meaning the diameter of headspace comparator bushings don't actually have to perfectly match the angle and diameter of the datum line at the contact point in the chamber.

More commonly, I simply slide shim stock against the base of the case, or even use tape as shimstock, instead of using the spent primer as a depth gauge. The end result is the same no matter what method you use.

"...he has headspaced using primers..." No, he hasn't. The primer depth has nothing whatever to do with headspace.
"...Not sure about the 7.7 Jap..." Rimless case just like a .30-06.
"...no SAAMI maximum for 7.7 Japanese..." No 7.7 Jap SAAMI specs listed at all. Isn't listed by CIP either.
"...even use tape as shim stock..." Tape is totally useless for anything headspace related. Tape is just paper with one side sticky. And it compresses.

This thread has me thinking I could just use plastigauge, layed on the head of a used case from the rifle in question. I use them for measuring bearing clearances on engine builds. http://www.plastigaugeusa.com/how.html

One way, use Cerrosafe, molten sulfur, or Woods metal (generic Cerrosafe) and take a chamber casting. Obviously need to know how to do it but instructions on Cerrosafe can be found at Brownells and they do answer their phones. Molten sulfur has been used but takes a delicate touch and the generic Woods metal might or might not have the same thermal properties of expansion and contraction depending on the alloy--my advice is to go with Cerrosafe. One thing that casting does relative to other methods is that it will also tell you throat condition and whether the chamber has been altered by comparing the cast with the chamber drawings and dimensions above. Use the shoulder reference and calipers and should get a good reading of headspace.

A second way is to use Hornady's case headspacing tools in conjunction with a accurate caliper. Need to take accurate measurements before and after firing of the case with it. However, the trick is that you have to testfire it--I advise remotely using a hydraulic trigger release with firearm in a recoil absorbing cradle.

A third way, some add layers of scotch tape (the 3m brand name stuff and not generic) to a no go gauge until it reaches resistance or use shim stock. Have to have the right touch not to compress the tape or shim stock.

Fourth way, there is a universal headspace gage that comes from Germany I believe,from my remembrance, if you have to ask for the price, you probably don't want to buy it.

Fifth way, contact PTG or Manson to make a custom Arisaka Field headspace gage and pay the toll for the special job.

My Arisakas are from 1942 and earlier so not much affected by wartime expedient production but late 1944 and 45 production quality might warrant having a gunsmith check it if you are not sure how to check a firearm for overall safety. Headspace is an issue but simply one of many on some of these old rifles. For example, one invisible problem if you have not taken the action out of the stock is pitting below the wood line of the stock or an altered safety.

While OK for a rough guess, any headspace checking "system" that uses ammunition or cartridges is not going to give good results, for the simple reason that cartridges vary too much and, after all, one of the purposes of a headspace check is to make sure out-of-spec cartridges won't be accepted.

Jim

Jim K said:

While OK for a rough guess, any headspace checking "system" that uses ammunition or cartridges is not going to give good results, for the simple reason that cartridges vary too much and, after all, one of the purposes of a headspace check is to make sure out-of-spec cartridges won't be accepted.

Jim

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Jim,
Actually, you can get pretty exact headspace compared with gauges using the Hornady system (formerly Stony Point). The typical gage set is too long (nogo), too short (go), and way too long (field) plus a tolerance factor. For .223/5.56 and .308/7.62 there are expensive ten gauge headspace sets to get very close to the actual headspace that I believe Brownells and a few mfgs sell direct. The key to the Hornady set is to accurately measure the case before and after firing (one caveat is that you must use "normal" loads so you get case expansion and not powder puff ones). Just like fireforming, the case expansion gives you the overall headspace. The rub is that if you do not know whether you have grossly excessive headspace, you still have to fire a cartridge in the rifle to find it. Some actions don't have good gas handling especially antiques so you possibly could destroy the action by firing it to test for excessive headspace.

Live or Dummy Cartridges do okay as a sub for bolt action go gages but given that bolt actions have enough leverage and brass is springy enough that your headspace may be a bit short SAAMI wise. Definitely not recommended for semi-autos as a practice.

I have heard somewhere of doing it with spent primers and cases but never done it nor plan to.

Quite a few people use tape and shims for rimmed case headspacing using coin type gages.

The problem using a fired case it that it takes 3 firings to get a accurate representation of you chamber due to spring back. This is one of the reason brass is the preferred material for cartridge brass. Also letting a bolt slam close on a auto can bump the shoulder back 0.002". Now the Hornady tool is just a compairator unless you check it with know standard. They very from tool to tool so it's mainly used as a reference.

tie it to a old tire and shoot it, i don,t think i ever saw a 7.7 japanese rifle with the correct (reciever-bolt matching numbers) bolt that had headspace. and i played with dozens of them in the late 50,s as i collected them. the japanese rifles(model 38-99,s) were very strong.eastbank.

Blue68f100 said:

The problem using a fired case it that it takes 3 firings to get a accurate representation of you chamber due to spring back. This is one of the reason brass is the preferred material for cartridge brass. Also letting a bolt slam close on a auto can bump the shoulder back 0.002". Now the Hornady tool is just a compairator unless you check it with know standard. They very from tool to tool so it's mainly used as a reference.

Click to expand...

First, we are talking about an Arisaka which is a bolt gun. One has to use headspace gages for semi-autos generally and you NEVER let the bolt slam home on them period even in a bolt gun. Even steel can compress and you'll ruin your headspace gage. Second, you have to compare every measurement to some std.--even headspace gages-for example there are two different shoulder angles for the Mauser 98 in 8mm depending on when it was produced--the gages will produce different results because the known standards for the chamber are different. You should not even mix brands among headspace gages if you want accuracy. What will pass a Forster, may not pass a Manson, etc. Then you have rimmed cases where the shoulder is not involved at all and the semi-rimmed such as the Japanese Arisaka where it is and isn't. Sometimes the gages themselves are made to a standard that is not what the issuing military used because SAAMI differs from the original--e.g. Swedish Mausers or for the .303 Enfield or they use CIP instead.

The O/P's question here is what alternative methods can be used to check headspace when gages are absent or expensive. If you have oddball cartridges then you have to use some method. Using before and after fired brass, give you clear indications of excessive headspace and btw, you get better and more representative results if you wish using about ten cartridges. I generally use a box of twenty (and yeah, I know ideally even more gives more accurate results) but I normally use them when headspace gages are not available and some old milsurps are a PITA to get a chamber casting out of if the throat is rough. On a few of my rifles, I use them to craft more accurate handloads which was the original purpose. If you want exact headspace for a rebated rim cartridge, then you have to take a chamber cast (or perhaps use that universal tool made in France I believe). Chamber gauges (apart from the expensive ten gauge sets) generally give you three options--headspace too short (go), too long (no go), and excessively long (field).

The chief risk of headspace in bolt guns being excessive (other than grossly excessive such as firing the wrong cartridge or defective double charges etc. in a rifle) is hot gas from case separations which is ill handled by some rifles including Mausers before the 98 Model and Springfields (especially those early ones that don't have the Hatcher hole which you really should not be firing anyway by some accounts). Ironically, rimmed cartridges that were considered "obsolete" such as the 7.62x54r, the .303, and the Lebel, and the .30-40 Krag, are easier to check for excessive headspace and the cartridge rim acts to some degree to seal and deflect gases from case separations caused by an imperfect chamber.

It can be alleviated to some degree by fireforming cartridges and only using them in that particular rifle or by using powder puff type loads that don't stretch the brass very much. However, depending on the chamber, brass life may still be significantly less and you do have to do case inspection after each firing. Lee Enfields have a just reputation for having usually overly large chambers and short lived brass.

Semi-autos are are a different case due to the need to full length resize cartridges to avoid out of battery firing, the need for a certain cartridge pressure and or generated recoil to operate the action, and accuracy/feeding issues. There, headspace is more of an issue than just cartridge separations.

BTW, I also have an experienced three generation family of gunsmiths familiar with milsurps check my firearms before going whole hog in developing loads for them to find anything problematic that I have missed. It is cheaper than the copays on my medical insurance.