Headspace gauges

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Potashminer

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Had a conversation today - am now wondering if I had been misled in the past.

I know there is a GO gauge - ground to represent minimum (shortest) headspace for a chamber - dimension is referenced on SAAMI drawings.

I know there is a FIELD gauge - ground to represent the maximum (longest) headspace for a chamber - dimension is also referenced on SAAMI drawings.

I was told (maybe I misunderstood) that a Military Armourer had ONE gauge - a FIELD gauge - if chamber was too short, the rifle would not have got out in the field - the fact that the soldier had fired it with service ammo proved it was not too short. The Armourer's job was to decide if the arm was safe for continued service - if would not close on FIELD, it was good to go, in-so-far as headspace went.

Then barrel makers, or commercial, invented the NOGO gauge - is not referenced in SAAMI dimensions that I could find - so often .004" longer than GO gauge - simply to be used when installing a NEW barrel - so installation is to be more than GO length, but less than NOGO length. Which is a LOT shorter than FIELD length.

Do I have this correct - can any former military armourers confirm what they had or used for gauges in the field, in service?? No doubt is not the same as for maximum precision, bench rest, etc. - application is for "in use" or "used" service rifles.

The 30-06 gauge set I have contains three gauges - GO, NOGO and FIELD - which one or ones would you use to evaluate a WWI military 30-06 rifle for head-space??
 
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I would say you are correct. If it closed on a field guage would mean it was over the max spec for war time and taken out of service.

If your 30-06 DOSENTclose on the field guage. Its safe enought to use in war time

303br field guage is i think 0.010 more head space then sammi allows for max headspace.

I see a field guage as the max allowed head space before it may be dangerous.

Go and no go set a safe standard that is easy on on the brass and rifle and makes sure all inspec ammo will chamber
 
tiriaq - I just looked at SAAMI 2015 - calls out .064" as minimum and .071" as maximum for the rim recess "head space" in a 303 British chamber - so your .074" must be a military FIELD (maximum) size. I had read somewhere, that at differing times the British, Canadian and Australian militaries called out differing sizes - but none of them were / are required to abide by SAAMI.
 
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If you're doing a build, use the GO gauge. You're not going into battle and maybe using dirty or out of spec ammo.

Keep your headspace as tight as possible.

I've assembled P17s in the past, using just the GO gauge with the bolt just closing without force, other than overcoming the spring tension.

Yes, I use the fully assembled bolt to check headspace. No surprises that way.
 
I picked up a M17 barrelled action that closes on a No-Go gauge. So other than setting the barrel back I guess the action is kaput ? As well Bubba welded then ground the rt inside bottom feed rail so I think it's pretty much parts now? Shame the sporter barrel is VG
 
I just looked in the SAAMI 2015 standard for 30-06 Springfield - they call out headspace dimension as Minimum 2.0487" and Maximum as 2.0587" - so 0.010" difference - allowance for "wear", I presume. I have no clue what length various gauge makers actually grind their gauges to - the Clymer brand gauges that I have are not marked for their dimension - the label says "SAAMI Spec", which is curious, because I do not see a NOGO length called out anywhere on the SAAMI drawings, unless elsewhere is described, by SAAMI, as a certain amount greater than the minimum dimension.

I believe it is a thing for precision builders to want to set headspace within a .001" or .002" of minimum - that would be GO gauge. I think commercial guys want headspace within .004" of minimum for a NEW installation - so close on GO; not close on NOGO. But for evaluating a used chamber / bolt seats, etc. SAAMI seems to say so long as headspace dimension is less than Maximum (FIELD gauge), then a SAAMI compliant cartridge will not be dangerous - will not burst.

A home hand loader can mostly ignore all that, I think, by making his brass fit to his chamber, whatever the actual head space length might be - within reason. Sort of like "chasing the lands" for bullet seating depth. For sure, the military concern was different than perhaps a modern reloader - military, that I know of, was to fire a standard military round - once - extract and eject and fire a "new" round - were never, ever concerned about reloading the previously fired case - like we are. I do not think the military designers even considered whether the fired case was suitable to be re-sized and re-loaded - simply not what they did...

And it would not be a surprise, at all, to learn that WWI US Army, or 1950's BSA used different length GO and FIELD gauge than what SAAMI calls out for commercial use as of 2015? I do know at times there were different dimensions called out by each of British, Canadian and Australian military for the 303 British cartridge, so no doubt similar was done with the 30-06 Springfield.
 
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Potashminer said:
I just looked in the SAAMI 2015 standard for 30-06 Springfield - they call out headspace dimension as Minimum 2.0487" and Maximum as 2.0587" - so 0.010" difference - allowance for "wear", I presume. I have no clue what length various gauge makers actually grind their gauges to - the Clymer brand gauges that I have are not marked for their dimension - the label says "SAAMI Spec", which is curious, because I do not see a NOGO length called out anywhere on the SAAMI drawings, unless elsewhere is described, by SAAMI, as a certain amount greater than the minimum dimension.

I believe it is a thing for precision builders to want to set headspace within a .001" or .002" of minimum - that would be GO gauge. I think commercial guys want headspace within .004" of minimum for a NEW installation - so close on GO; not close on NOGO. But for evaluating a used chamber / bolt seats, etc. SAAMI seems to say so long as headspace dimension is less than Maximum (FIELD gauge), then a SAAMI compliant cartridge will not be dangerous - will not burst.

A home hand loader can mostly ignore all that, I think, by making his brass fit to his chamber, whatever the actual head space length might be - within reason. Sort of like "chasing the lands" for bullet seating depth.

And it would not be a surprise, at all, to learn that WWI US Army, or 1950's BSA used different length GO and FIELD gauge than what SAAMI calls out for commercial use as of 2015? I do know at times there were different dimensions called out by British, Canadian and Australian military for the 303 British cartridge, so no doubt similar was done with the 30-06 Springfield.
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Military specs take into consideration such things as dirt/mud/blood/snow and even water, when they set their specs. Wear has little to do with it.
 
Potashminer said:
SAAMI is not a military spec, that I know of. SAAMI calls out .010" difference between Minimum and Maximum for the 30-06 Springfield.
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Sorry, I thought you were referring to the differences between SAAMI and Milspec. My bad.

Still, I would set up any build to SAAMI minimum spec, if the chamber will allow it and still index properly.

When putting a rifle, such as the P17 together, it's often neccessary to to live with what you have, if you want to the barrel to index properly. Once in a while, some metal can be removed from the shoulder, to get it into position, which will often only be a few thou and headspace will still be acceptable.

The ones that make you cringe are the barrels that go way past the proper index point.

I've gone so far as to set back the shoulder and make up a shim to achieve the proper index point.

I find that a shim, at least .065 thick will give enough tension when tightened not to deform or be visible.

If the headspace is to tight, after fitting the shim, it's an easy fix.
 
I have done the same - I think British called it a "breeching washer". Would be so much easier to do if I had chamber reamers, but I don't, so usually multiple shenanigans to make old stuff work. P14 and M1917 are important to hit that index, I found - just for that slot cut in barrel for the extractor. Is added "spice" compared to making flat rear end of a Mauser work.

And, as you say - hitting the index marks usually important to get iron sights to top dead centre - I have learned sometimes have to live with "close", not perfect, in order to use the original chamber. I have a Remington 788 action that does that - I tried 3 different factory take off barrels - I had to settle for "closest", to achieve headspace with their original chambers and at same time to get sight holes to top dead centre. Achieve correct headspace first. Then try to deal with sight holes and scroll marks.
 
I know you have the tools/skill, so why haven't you attempted to make your own "D" reamers from Drill Rod????

It's all part of the fun in keeping these old girls going.
 
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bearhunter said:
I know you have the tools, so why haven't you attempted to make your own "D" reamers from Drill Rod????

It's all part of the fun in keeping these old girls going.
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Sorry to the OP on the tread hi-jack but Interesting timing on mentioning D reamers, I am just putting to paper a design on a build that will require a one-off reamer (45-90,50-70 or 50-90). I am starting to build a 'bucket list" project, a 1/8th size 155 or 105 WW11 artillery piece with an "interrupted thread" breach-block and the one of the above calibers will be the chosen "rimmed replica" artillery rounds.

Bear, do you have any tips for making a usable reamer. I have read about them years ago but never got around to building one.
 
fingers284 said:
Sorry to the OP on the tread hi-jack but Interesting timing on mentioning D reamers, I am just putting to paper a design on a build that will require a one-off reamer (45-90,50-70 or 50-90). I am starting to build a 'bucket list" project, a 1/8th size 155 or 105 WW11 artillery piece with an "interrupted thread" breach-block and the one of the above calibers will be the chosen "rimmed replica" artillery rounds.

Bear, do you have any tips for making a usable reamer. I have read about them years ago but never got around to building one.
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Rather than going into depth on it here, there are some excellent videos available on the net.

It's not difficult to turn the original diameter of the Drill Rod, but you should soften it up first, before turning/milling/grinding. Then harden it again and do your final grind to the cutting edges.

"D" reamers only have one cutting edge, so you're much more dependent on the pilot to keep it cutting straight.

Another thing, you really need a lathe that is able to turn VERY SLOWLY, while appling lots of lube and making shallow cuts.

Because they only have ONE cutting edge, pay attention to how sharp that edge is. I usually check it after every pass.

USE LOTS OF LUBE.

If you don't use lots of lube and keep the edge sharp as well as spin it to fast, you will get chatter, which could prove disastrous to the job.
 
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