Using a rimmed cartridge headspace gauge

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MrMagumba

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Hello all. Forum newbie here so please excuse any breach of etiquette. I'm considering rechambering my modern rifle to a somewhat obsolete cartridge. I am trying to understand how a gunsmith would cut the new chamber. I have done some homework-You tube videos, reading forums, emailing tool companies, calling gunsmiths- but some of these sources don't have time to educate me for free. The thing I'm stuck on is "how can a chamber be reamed to the proper depth when the headspace gauges for rimmed cartridges in the catalogs claim to be usable for multiple length cartridges?" (30-30 gauge claims to be usable for 375 Win, or in the case of belted cartridges 300 Win Mag is also used for 7 MM Rem Mag- which are different lengths. The 375 Win also has no shoulder.)

So I assume these gauges are used to get the headspace correct for a given rim thickness or belt dimension, but the question again is "how do we cut the proper chamber depth?" For rimless cartridges, all the videos I've watched show the gunsmith using a headspace gauge to cut the proper depth. This makes sense since the headspacing uses the shoulder as a reference, and there are no claims that this style of gauge can be used for different length cartridges.

Ok thanks. I'll probably post more about my particular project, but trying to understand this first. I chose the reloading forum for this, because I'll probably follow up with discussion of how to get my brass to fit the chamber.
 
This makes sense since the headspacing uses the shoulder as a reference,
Click to expand...

No ... Not headspacing for a rimmed cartridge ... it is the thickness of the rim that controls headspace ....

What you are searching for is a "Go/No Go" Chamber gauge set ... not really a headspace gauge.

Here is a link for .303 Rimmed head space ... it says it is a no go for headspace ... but you should get the ideaa from the photo...

http://ads.midwayusa.com/product/113654/ptg-headspace-no-go-gage-303-british


This is just like the .375 H&H based cartridges ... belted type ... a headspace gauge is just the semi rim, the belt and a short section of the chamber(for alignment only) ....

http://www.brownells.com/gunsmith-t...inks-_-Landing+Page-_-CF_Measuring_Tools_Main
 
Last edited:
"...30-30 gauge claims to be usable for 375 Win..." Same headspace gauge due to both headspacing on the same rim dimensions. The .375 is just a .30-30 necked up. Belted cases headspace on the belt.
We cut the proper chamber depth the same way it's done for any cartridge.
"...a "Go/No Go" gauge set..." Um, those are headspace gauges. Headspace gauges do not measure anything. They only tell you if the headspace is within tolerance. They come in 'Go', 'No-Go' and 'Field'. The latter has nothing to do with the or 'rejecting' anything.
 
I've moved this to gunsmithing, since it's a gunsmithing question rather than a handloading question.
 
Sunray ... I tried to explain the difference by using photos ...

Why don't you take the time to explain what you are saying instead of being so condescending ???
 
Thanks for the quick replies. I tried to be careful using the word headspace. I have read many forum posts where the "H" word causes misunderstanding. Obviously it has a lot to do with my question and I think I have a fairly good understanding of it now. What I'm reading from JimKirk is that there is a "headspace gauge" for setting headspace on a rimmed cartridge and a "chamber gauge" for cutting the depth of the chamber. If that's true then it explains a lot. If that is not what was meant, then I think I'm back at square one-"how does a gunsmith cut the chamber depth of a rimmed cartridge?" For a rimless cartridge, one gauge would serve both functions-headspacing and chamber cutting since the headspace is controlled by the length of the chamber. So is the consensus that I have my answer?
 
Mag ... as you can see there are gauges just to "check" the actual headspace on a "rimmed" cartridge ... they have nothing to do with the chamber itself ... that is why they only have the "rim and a short section of body" ... they really only check to see if "it" in in specs or out...

Yes there is a lot terms that thrown towards the word headspace ... makes it confusing to many ... I'll admit it is confusing to me at times...

What cartridge are you considering?
 
I'll tender this as a gross over simplification.

Rimless cartridges are held in position by their shoulder on the front and the base/rim on the back. Rimmed cartridges are held in place by the rim alone. So headspace is responsible for positioning the cartridge in the correct spot for firing, some by the shoulder/rim and some by the rim alone. There's a lot more to it than that, but the concept should clear up the issue.
A chamber can have all kinds of nasty problems other than those which can be measured by a headspace gauge. the Gauge alone is no guarantee of safety or proper function.
 
Well since you asked, and since I think I have the answer to my original question, I'll tell you what my project is, and at best gather more info so I can have an intelligent conversation with whoever I ask to do the action work. At worst I'll open a can of worms, but that might teach me something as well. I have a 700 short action that I want to make into a 6.5 Jap. I am trying to learn and forecast how a gunsmith would cut the chamber, to head off problems. I'm wondering what kind of tools (reamers, headspace gauges, etc.) would be ordered or be laying around gunsmith shops. I wondered if I just ordered a reamer or gauge from Clymer or Pacific Tool, what would I get? Clymer did not respond, but Pacific sent me a drawing of their reamer which satisfied me, so I then asked if they could supply a matching headspace gauge, and haven't gotten a response. Obviously, since I'm using a 700 action, I'll be headspacing on the shoulder, but my Arisaka relies on the rim to headspace. The 6.5 Jap is a "semi-rimmed" case. That is what raised my curiosity as to how the different gauges are used in practice, and what I might get if I ordered one in the blind. If I was building a SAAMI spec gun I could just order it and it would be fine. Since it is an old cartridge that has only a CIP spec that has been revised a few times I need to verify that the tools will give me something I can shoot and reload for. Building ammo for it will be another engineering "wonder of the world". I'm not a glutton for punishment, I just think this stuff is really interesting to work with.
 
Thanks ... Mag...

I am sure that your project will be interesting .... I am sure someone somewhere has done or thought about doing something very similar ...
 
Before you get all wrapped up in chamber reamers and headspace gauges, might want to figure out how to get a 700 bolt face to work with a semi-rimmed case. The two are quite different.
 

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Well for starters, the 6.5 Jap is not a rimmed round.

It measures .447" at the rear of the case, and .466" at the rim.
So semi-rimmed, which isn't the same thing as a rimmed cartridge.

So, it head-spaces of the case shoulder just like all modern bottle-neck rounds.

The .466". Case rim is usually compatible with the common .308 / .30-06 case head when it comes to bolt face and extractor compatibility.

Thousands of them were converted to .257 Roberts after WWII when 6.5 Jap ammo was unattainable.

All that was done to them was run a .257 Roberts chamber finish reamer in them.
No bolt face mods necessary.

Again, it head-spaces on the case shoulder, not the rim.

Next question??

Why in the world would you want to convert a Rem Model 700 in ANY caliber to 6.5 Jap?????

rc
 
Thanks for thinking about my project and bringing up the bolt face issue. That is actually one thing I thought about. I was able to cycle 6.5 Jap ammo through my 260 Rem 700 action (that's not the gun I'm converting). Otherwise the project would be even less feasible.

As to why... Well that's a long story. but it is mostly for nostalgia. I have managed to come up with practical reasons (excuses) for this, but it is just for fun. I still need to figure out the ammo issue before ordering the gun, so perhaps I'll see you over in the reloading forum. Thanks all.
 
I think I would locate an old fashioned gunsmith, buy a case of ammo or brass, and have him chamber the barrel to accept the actual round to be shot.

Save the worry and expense of trying to find gauges for an obsolete foreign caliber.
 
Hi, Rcmodel,

Your comment that the 6.5x50 was not supposed to get its support (headspace) on the rim is interesting, as that is usually the reason for having the rim at all. I have not done extensive measurements or a chamber cast, but the breeching in a Type 38 certainly looks like it is intended to support the rim. I have not read anything on the reason for choosing the semi-rim (and I doubt any information still exists), but it seems to have been a compromise between having a full rim for better extraction and having no rim to interfere with feeding. (At least that is why Browning chose semi-rimmed cartridges for his early pistols; later he learned about Luger's use of the case mouth and the light dawned.)

Jim
 
I was wondering how well rcmodel's straight .257 Roberts rechambering works.
I have long read of the 6.5 - .257 wildcat (practically identical to 6.5x57 Mauser) but that is not what he describes.
 
SAAMI is the source of most of the confusion about "headspace". SAAMI has a definition for headspace that is based only on the bolt and chamber:

http://www.saami.org/glossary/display.cfm?letter=H

HEADSPACE The distance from the face of the closed breech of a firearm to the surface in the chamber on which the cartridge case seats.

SAAMI does not have a "headspace" definition based on the cartridge. This omission is deliberate and is, I believe, based on the fact SAAMI is the society of Ammunition and Arms manufacturer's. This group is not interested in reloading or reloaders. SAAMI wants to sell you loaded ammunition or unfired cases. If you decide to reload those cases, you are costing SAAMI members profit.

Reloaders should recognize that SAAMI definitions intentionally do not support critical issues with reloading cartridges. There needs to be a definition establishing the base to seating shoulder distance on cartridges. With respect to rimmed cartridges, this distance is just as important for a reloader, as the base to shoulder distance is for rimless cartridges. Regardless of the clearance between rim and chamber before firing, after firing, the shoulder will have moved. If during resizing, if the clearance between the shoulder of a sized rimmed case and the rimmed cartridge chamber is too great, the case will separate.
 
Following WWII there were thousands of captured Jap rifles brought home, and no ammo for them.

Enterprising gunsmiths rechambered them to .257 Roberts, even though the .264" bore was too large for the .257 bullets.

It must have worked well enough to pop a deer every fall, or make some noise on the 4th. Of July!!

Regardless they could buy .257 Roberts ammo at Western Auto and Bee Happy!!

As for why it is semi-rimmed?
I have no idea?
Other then it followed the 8x53R Murata rimmed round of 1889.
The 6.5x50SR was introduced in 1897, in a failed bolt-action design.
Then adopted in 1905 in the Type 38 Arisaka rifle.

(Belt and suspenders approch to a rimless design?)

The 7.7 came along in 1939 in both a semi-rimmed type 92 version for machine guns, and the rimless version for the Type 99 Arisaka rifle.

My comment on chambering a new barrel to headspace on the shoulder is only my personal belief.

No 50,000 PSI bottle- neck rifle cartridge should depend on a semi-rim to headspace it if you have a shoulder to do it perfectly, better.


Rc
 
rcmodel said:
...My comment on chambering a new barrel to headspace on the shoulder is only my personal belief.

No 50,000 PSI bottle- neck rifle cartridge should depend on a semi-rim to headspace it if you have a shoulder to do it perfectly, better.
Click to expand...

^^^^ That right there! If you actually think about what happens in the chamber when the round is fired it makes perfect sense. Why work you brass to death when you can chamber the barrel and/or size the round to headspace off the shoulder vs the tiny vestigial rim, or any rim for that matter. I think the same about belted magnums and their (variable dimension) belt. Along with better case life you potentially gain accuracy benefits.

As a side note the reason GC Nonte (I served in the Army with Nonte's daughter, a fine Intel officer) came up with the idea of headspacing the 38 Super pistol round off the mouth vs the rim was more about accuracy than case life, but it proved critical in saving that round from an inglorious demise. I've built some very accurate 38 Supers using case mouth defined headspace since my first factory stock spray-em-all-over-the-place 38S Commander.
 
True, SAAMI defines bottleneck rifle "headspace" only in terms of the gun's dimension from bolt face to stop surface, whether rim recess/belt recess, or datum circle on the shoulder.

But they also show corresponding dimensions for the cartridge, including:
Cartridge casehead to front of rim/front of belt, or datum circle on the shoulder.

Interestingly enough, it's not "or", it's "and."
They show both those dimensions for rimmed or belted cartridges and their chambers.
The official headspace control for a rimmed round is the rim seated in its relief in barrel breech or bolt face. But there is also a specification for the boltface to datum circle on the shoulder. It isn't called "headspace" but it is measured the same way.
Likewise the cartridge.

Which brings us around to the frequent recommendation in reloading, that the rim be ignored and the case sized to just allow free chambering with the cartridge shoulder up to the chamber shoulder just as you would a rimless caliber. Longer brass life, don'cha know.
 
I like to buy a lifetime supply of rimmed cases, measure the range of rim thickness, cull some thick ones, and make up my own headspace. With 303 there is a huge range.

Then make the headspace gauge on the lathe.

Because of interference with the extractor and extractor relief cut when rotating to fit a feeler gauge between barrel and receiver , with Mosin Nagants I made up a headspace + one barrel thread turn ...gauge.

Likewise with belted magnums, I get the lifetime supply of brass, and survey the distance to the belts on the cases. SAAMI is 0.220", but I am 0.215".
 
FWIW, I have several 7.7 Type 99 Arisakas and the same in Type 38 in varying barrel lengths. The 6.5x50 is a nice sedate round that kinda pokes along without much noise or fuss. The 7.7 feels and acts like a .303 which is not surprising.

There is considerable debate in milsurp groups regarding how to determine when a 6.5 has excessive headspace because of that semi-rimmed characteristic.

You can look around and find some sporterized Arisakas for pretty reasonable if you can overlook the safety which I find personally easier to use than the Mosin but that is not saying much. Using the heel of your hand is key.

That being said, why not adopt the the 7.7 Japanese for your conversion rather than the 6.5. The 7.7 closely resembles the .303 cartridge in power which is pretty versatile and is a rimless case. The brass is easier to case reform if you want from 8mm Mauser brass. .311 Bullets are available to handload.

4D Reamer rentals also has reamers and headspace gauges for rent in 6.5 and 7.7 Japanese http://www.4-dproducts.com/displayitem.php?rowid=459&tname=rental http://www.4-dproducts.com/displayitem.php?rowid=107&tname=rental
 
Remmber that SAAMI is an industry standards group; its job is to provide the manufacturers with specifications for cartridges and chambers so that X company's cartridges will fit and fire safely in Y company's rifles. Headspace is only one of those specs. Even if a case is rimmed and headspace is based on the rim area, the base to shoulder measurement is critical. If it is too long, the round won't chamber, no matter what the headspace is.

Jim
 
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