Checking headspace LR308 build

[Bart B.]

Years ago, a neighbor showed me his adjustable headspace gauge for 30-06 barrels. Its front half had a set screw to lock it in place when indexed on its scale. The scale went from -5 to +10 with zero being a GO gauge spec of 2.0487". Set it to where the bolt barely closed on it then the chamber headspace could easily and precisely be determined. I don't see any such gauges available now.

A simpler and almost as precise way is to compare a fired max load case headspace to that of a GO gauge. Such fired cases are about .001" less than chamber headspace. Case headspace gauges are available from Hornady and RCBS. Use one to measure your resized case headspace and set the die such that they're .002" less than after firing And before sizing. Best accuracy and case life happens doing this.

 

[fguffey]

A headspace gauge is made to dimensions specifically established for the particular cartridge. It is the length that will replicate a cartridge manufactured to the minimum length the will fit in a chamber cut to minimum or maximum length and still have acceptable headspace.

The case length from the shoulder of the case to the case head from the factory is called minimum length/full length sized. The go-gage is .004" longer from the shoulder of the gage to the gage head than a minimum length/full length sized case.

F. Guffey

 

[1stmarine]

The go is an estimate and it changes between brands and purpose. It is often used as a safety measure but it is also used to tune up the chamber for accuracy like match shooting.
The go gauges I have for the 308 are 1.632, 1.636 and then a few no go and field gauges.
My redding dies will resize brass snug to the 1.632 gauge (Forster) and a tad loose for the 1.636 so for a tight match chamber I will work with the shorter gauge.
I head-space using the resized brass and ends up 2-3 thousands larger than saami minimum that is 1.630 for the 308W and its siblings.
Still one can play with different shell-holders but I barely use them because like many of you might neck size after fire forming.
Either way still considered good chambers on the GO assessment and federal gold match likes the tight chamber.

 

[fguffey]

New

The go is an estimate and it changes between brands and purpose

If that happened with my gages I would want my money back. When I close my micrometers they 'ZERO', when I measure a gage I verify.

F. Guffey

 

[1stmarine]

New


If that happened with my gages I would want my money back. When I close my micrometers they 'ZERO', when I measure a gage I verify.

F. Guffey

The go gauges are different sizes for a reason. Lets say forster vs. ptg std.
How do you measure them with the micrometer and zero to what measure exactly?
I am not trying to question your methods but to understand how and why.

 

[fguffey]

The go gauges are different sizes for a reason.

The go gauges

The go is an estimate and it changes between brands and purpose.

you have "go gauges", before that you have "The go gage"; for me there is only one length for the go-gage, there is one length for the no go-gage and then there is the field reject length gage. I have never had the same problems reloaders had/have with the Hornady comparator because I understand they use a radius on their datum. If I am going to use the Hornady comparator for comparing SAAMI specifications I am going to determine how far off the Hornady tool is. The Hornady tool is a comparator as in greater than or less than; shorter than or longer than.

F. Guffey

 

[1stmarine]

Sorry for asking again but I am still trying to understand.
What is the right length for the go gauge?
How do you measure your go gauge with the micrometer?

 

[Bart B.]

For gauge dimensions, start on page 212 in

http://www.saami.org/specifications_and_information/publications/download/Z299-4_ANSI-SAAMI_CFR.pdf

then study the gauge drawing. Letters in boxes have an arrow to a point in the gauge which are listed on the following pages.

Look at page 214 to see 308 Win headspace gauge minimum (GO, 1.630") and maximum (NO GO, 1.640") dimensions in column F.

To find these dimensions on a gauge or case, you measure from from its head to the .400" diameter on its shoulder as stated in column M for the 308. A good tool is the RCBS precision mic. It's set to read zero on a 308 Win GO gauge. If it reads +.003" on a case, that case has a headspace of 1.633" to the .400" diameter on the case shoulder. If a GO gauge is in it and it reads -001", that gauge is 1.629" from head to that .400" reference diameter in the gauge shoulder.

 

[fguffey]

How do you measure your go gauge with the micrometer?

I ask if the field reject length gage could be used to determine the length of the chamber from the shoulder of the chamber to the bolt face. I do not know how to say I do it all the time without upsetting someone. I measure the length of a 30/06 chamber with a 280 Remington case; I know, the 280 Remington case is .051" longer from the datum to the case head than the 30/06 case from the datum (same datum diameter of .375") to the case head. The fact the bolt will not close does not bother me; the difficult part is convincing someone it can be done.

The only way to measure the length of a case from the datum to the case head is with a round hole, to work the hole diameter must be exact and the hole can not have a radius. The round hole/datum of .375" is the only possible way to find a place on the shoulder of a 30/06 case because of the taper/cone. The hole is not the datum as in measured from, the hole locates the 'measure from' when the hole is drilled through a plate. The plate is a plane flat surface if the hole is drilled straight.

There are two improvements/modification that can improve accuracy and there are ways to modify tools like the go-gage, problem, convincing someone it can be done.

The LR308 has a barrel with an extension and then there is the bolt assemble. The OP said the bolt closes on the go-gage but was snug on the no go-gage. If there was something on a reloading forum that was called 'relax' we would be finished. Had he used a go-gage when checking the length of the chamber he could have determined the protrusion of the bolt from the extension and then chambered the go-gage. after chambering the go-gage he could have pushed the bolt into the extension: forgive:

I have something I have something that needs my attention...

 

[1stmarine]

For gauge dimensions, start on page 212 in

http://www.saami.org/specifications_and_information/publications/download/Z299-4_ANSI-SAAMI_CFR.pdf

then study the gauge drawing. Letters in boxes have an arrow to a point in the gauge which are listed on the following pages.

Look at page 214 to see 308 Win headspace gauge minimum (GO, 1.630") and maximum (NO GO, 1.640") dimensions in column F.

To find these dimensions on a gauge or case, you measure from from its head to the .400" diameter on its shoulder as stated in column M for the 308. A good tool is the RCBS precision mic. It's set to read zero on a 308 Win GO gauge. If it reads +.003" on a case, that case has a headspace of 1.633" to the .400" diameter on the case shoulder. If a GO gauge is in it and it reads -001", that gauge is 1.629" from head to that .400" reference diameter in the gauge shoulder.

Hi, I am familiar with the 308 dimensions.
I don' have the RCBS precission mic for 308 and only the typical set of micrometers, dials and gauges the average machinist and/or gunsmith has.
But if you have used this RCBS mic, have you ever found a gauge not measuring what the manufactured of that gauge specified?

New

If that happened with my gages I would want my money back. When I close my micrometers they 'ZERO', when I measure a gage I verify.

F. Guffey

When you do this what is the precise right measure for the gauge?

Thanks.

 

[Bart B.]

But if you have used this RCBS mic, have you ever found a gauge not measuring what the manufactured of that gauge specified?

Yes, because a .001" spread across the Mic's and gauges happens. But that's not important. Only the difference between your chamber and cases is what matters

 

[1stmarine]

Yes, because a .001" spread across the Mic's and gauges happens. But that's not important. Only the difference between your chamber and cases is what matters

Makes sense. what is the precise measure of the RCBS gauge? I understand the +/- 1 thou.

 

[Bart B.]

I don't know what gauge RCBS used to zero in place their Precision MIc thimble to zero with, but that's how they're calibrated.

You can do well using a nylon bushing with a 3/8ths inch inner hole as shown in this picture set:


Zero your caliper on the nylon bushing, then measure a fired case headspace, resize it again, remeasure. Reset your die in the press until fired cases resizes have their shoulder set back .002". These pictures show it being set back only .001" which might be a bit tight. There'll be a couple thousandths spread across several fired cases being resized. This is for the .30-06 case and GO gauge which have a .375" reference diameter on their shoulders.

If you can find a bushing with a 10mm diameter inner hole, you can use it on .308 cases as their shoulder reference, as well as their headspace gauge reference is .400".

A 10mm hole is .3937" diameter and that's at 1.642" length on the .308 gauge shoulder from its head.

A 3/8ths inch hole is .3750" diameter and that's at 1.667" on the 308 gauge shoulder from its head.

Hope I've got those right; I usually do trig correctly.

 

[1stmarine]

I actually fabricated a bushing machined and reamed from 416SS and I use a micrometer vs. the calipers.
But thanks for posting the pictures as this might be helpful to others reading the thread.
I guess there are two discussions happening here, both important but with different objectives.

A) someone has a rifle chambered and is looking how to measure the chamber to be safe for use.
Additionally one might adjust the brass during resizing so the brass is as close as possible to the actual
chamber and this way improving accuracy and brass life. Neck sizing only is the obvious choice for many too.

B) Someone is chambering a rifle or might have a chambered rifle but also a method to adjust headspace in
that rifle (ie: savage action with barrel nut or finding a bolt with different dimensions) so they are looking to
adjust the chamber dimensions to the optimal size for intended commercial ammunition and/or brass produced
by the reloading dies one is using.

People with a rifle chambered and w/o the possibility of adjusting headspace with a barrel nut might
still have the option to increase or reduce the chamber length by using bolts with different dimensions between
the face of the bolt in contact with the base of the case and the back of the lugs in contact with the action lugs,
of course, if different makes of the bolts they are available. This is what we concluded with the original post
as the no-go gauge indicated an
unusually large chamber with the bolt originally used to check headspace. Instead the op opted to return the barrel vs
trying other bolts but that is a different story.

I understand the methods you described for the goals in mind. I think I am coming more from the this second
approach (B) as the original differences would call for a reduction of the chamber length in the first place and
then one could resort to approach (A) for fine tuning and managing the remaining difference.

l am also hoping @fguffey can chime in to see if he can specify what is the precise measure for the gauge to
be valid and why. I am still confused about why anyone would discard one gauge vs. another.

I hope this is clear. I know this might not be easy w/o more pictures specially for the average reader and shooter but
at the same time is not rocket science.

 

[Bart B.]

Full length sizing dies also have headspace. It's the distance from the bottom of a standard shell holder that's against the die bottom to the cartridge reference diameter on the die shoulder. It's typically about .005" less than a standard GO gauge headspace for rimless bottleneck rounds or SAAMI chamber shoulder spec for belted rounds.

A standard rimless bottleneck chamber GO headspace gauge in the die and a shell holder on its rim will have about .005" clearance from die bottom to shell holder when the two are pushed hard together.

Setting a die in the press so it stops on the shoulder of a GO gauge in the shell holder is a raised ram puts the die near perfect for correct sizing. Then adjust the die for correct fired case shoulder setback.

 

[1stmarine]

I understand the dies provide tolerances. You can even play with different shell-holders that give you +/1 thou increments.
Redding sells those sets for people in competition or simply seeking a tighter or looser fit.
We are in the same page here.
I was hoping @fguffey could chime in to understand the logic behind discarding one gauge vs. another.

 

[fguffey]

Had he used a go-gage when checking the length of the chamber he could have determined the protrusion of the bolt from the extension and then chambered the go-gage. after chambering the go-gage he could have pushed the bolt into the extension: forgive:

I am back, a term that does not exist in reloading is end-play, I use end play to determine the length of the chamber in an 03 Springfield; the nice thing about end play is the measurement determines the length of the chamber in thousands or the difference in length between the chamber and chambered round or clearance. And then there is the gage that is too long and will not allow the bolt to close, It is obvious when the bolt will not close, determining 'by how much?' seems to be the problem for most smiths and reloaders.

Back to the LR308: Does the bolt in the extension have end play? Meaning does the bolt move forward in the extension when installed and rotated. If it does a gage is not necessary if the reloader use a depth micrometer. The reloader can determine clearance between a minimum length/full length sized case and the chamber by measuring bolt protruding from the extension in thousandths. But if the reloader has one gage and it is a field reject length we all know the bolt will not close; not a problem. The reloader can install the bolt and rotate to close, then pull the bolt back to seat. Once the bolt is seated the reloader can measure bolt protrusion from the extension, After measuring bolt protrusion the reloader can remove the bolt from the extension and then chamber a field reject length gage and then attempt to close the bolt; but we all know the bolt will not close because the gage is too long (back to 'how much' too long). All the reloader is required to do is measure the bolt protrusion and then compare the two bolt protrusion measurement; I understand there are three gages, none of the three gages indicates the length of the chamber in thousandths. The go, no-go and filed reject length gages are 3 lengths out of 14 for the 30/06 length chamber from minimum length to field reject length. I want to know the length of the chamber in thousandths, there are at least three different ways to measure the length of the chamber in thousandths form the shoulder of the chamber to the bolt face.

F. Guffey

 

[fguffey]

I was hoping @fguffey could chime in to understand the logic behind discarding one gauge vs. another.

Logic behind discarding one gage vs. another? With end play I can determine the length of the chamber with a go-gage, I can also determine the length of a chamber with a no go-gage and I can determine the length of a chamber in thousandths with a field reject length gage. If a reloaded has the ability to measure the length of a case from the shoulder of the case to the case head he should be able to determine the length of the chamber in thousandths.

Years ago I purchased fired cases from firing ranges, one range allowed me to measure the length of the cases from the shoulder/datum to the case head. I had no use for cases that were minimum length or shorter than a go-gage in length from the shoulder/datum to the case head, I wanted cases that were fired in worn and stretched chambers. For me it was easier to sized cases to fit the chamber than it was to go to the range, fire to form then return and then size the cases. Manufacturers do not sell cases that are too long to chamber so I purchased once fired cases for as little as 5¢ each with 10 extras incase there was something wrong with the 100 cases.

F. Guffey

 

[1stmarine]

Hi,
I understand the clambering process. I have done this for a long time.
I am still confused about the criteria for rejection so I was hoping you could give me me the measure because when you said you measure the gauge
and verify what is the measurement you are working with? It has to be 1.6 something right? What is it?
If you don't have it is fine but then why reject something based on unknown measures?

New

If that happened with my gages I would want my money back. When I close my micrometers they 'ZERO', when I measure a gage I verify.

F. Guffey

Thanks.

 

[1stmarine]

Sorry I replied at the same time as you. Again, I understand the chambering process. I know we all have situations with brass and different chambers
but that is not my point. The issue is what would make you reject one gauge vs. another? I have no reason to doubt the printed lengths in the gauges I
have are wrong even if they are different.
Forster, PTG, mason, etc.. work with zero tolerances so I see not point in scrutinizing their gauges.
If you don't have the measure that is fine but then I don't understand the reason for sending a gauge back and what would be the measure you
would keep and why?
Maybe I am not explaining this the right way? All I would like to know is what you consider the right gauge. Is it 1.636" if not what is it?

 

[fguffey]

i,
I understand the clambering process. I have done this for a long time.

I will assume you meant 'chambering' and I do not know what you mean by "I have done this for a long time". What have you been doing for a long time? I can find no mention of any smith or reloader that that measures a chamber with any gage except the go, no and beyond gage with one exception. And then there is the modifying of gages as in one gage does it all from go-gage length to infinity or a more practice length that would be .016" longer than a minimum length/full length sized case for the 30/06 chamber.

If you do not believe it can be done as in measuring the length of a gage from the datum to the head of the gage please save my time and just say you do not believe it can be done. A recourse person on another forum was building a period correct Rock Island 03 for the year 1911. He was a member of a very dysfunctional forum called CSP. He asked for help and as expected his question turned into pages upon pages of responses by members seeking attention. I got involved when I purchased a mill from him, after loading the parts and pieces he as me about head space and then told me about his effort on the CSP forum. (Long story) But I did explain to him "this is your luck day". I explained to him I would help him determine the length of the chamber in thousandths without a head space gage. The first thing he handed me was a box of 20 head space gages for the 30/06 chamber. Two were from the time before SAAMI, the difference between the SAAMI specification and the time before SAAMI was the 'measured from'. Before SAAMI the length of the chamber was measured from the case body/shoulder juncture to the bolt face; that did not change anything having to do with the length of the chamber, all SAAMI did was move the measurement from the shoulder/case body juncture to a datum on the shoulder.

I checked the length of his chamber and I verified the length with ever gage he had in the box but I explained to him I thought it was nice to know the bolt will close on the go-gage and not close on the no go-gage but I wanted to know the length of the chamber from the shoulder to the bolt face. And that was the point; no one on the forum could tell me how to determine the length of the chamber in thousandths, he thought as long as he was building the rifle he would build the chamber go-gage length.

His chamber was .0025" longer than a go-gage and .0075" longer than t minimum length/full length sized case. After that he wanted to know how to reduce the length of the chamber by .0025", I informed him if bolts for the 03 were built to fit he could order another bolt; problem, he had no fewer than 100 Springfield bolts, I offered to check his bolts and the effect each one had on head space but I assured him he would not find one that would change the length .0025". I informed him I had no fewer than 25 03 replacement bolt and I assured him none of my bolts would change the length of the chamber .0025" plus he was building a Rock Island 03, at the time the 03 Rock Island had a straight handle meaning the rifle would not be period correct. He contacted John Beard; John came up with 4 bolts with straight handles bolts, I was not given the opportunity to check the bolts or the length of the chamber on his Rock Island build.

And then I showed him two more methods/techniques for measuring the length of a chamber without a head space gage. And I will tell you that was more than he wanted to know.

F. Guffey

 

[fguffey]

I do not verify with 'their' gage, I verify with my gage. I want to know the length of the chamber in thousandths. I want to know the length of the case from the datum/shoulder to the case head; I understand that makes no sense but I do not size cases for SAAMI chambers, I size cases for my chambers. I do not get involved in all the things reloaders claim can not be done.

F. Guffey

 

[Bart B.]

a term that does not exist in reloading is end-play,

There is a term for that, if you mean at the case shoulder, but seldom used.

It's called "shoulder clearance" and applies to rimmed and belted cases. When these cases are full forward in the chamber against their headspace stop, the space between case shoulder and chamber shoulder is shoulder clearance. At the back end of the case, that space between case head and bolt face is "head clearance;" a long time term is SAAMI's glossary.

Shoulder clearance is zero on rimless bottleneck cases as well as rimmed and belted bottleneck cases sized to headspace on their shoulders. I suppose then, rim and belt clearance to their normal chamber stop could be added to the list of names, terms and conventions. If there's shoulder clearance on a rimless bottleneck case when fired, its rim is against the extractor claw stopping the case from head spacing on its shoulder. Chamber headspace is too long or case headspace is too short.

"Mouth clearance;" the space between a chambered case mouth in firing position and the front end of the chamber neck. That space is where case necks go into from firing pin force driving the case forward setting its shoulder back. That clearance prevents case mouths "crimping" into bullets by the angled chamber mouth that would act like a stardard seater dies crimping shoulder at the die's neck. There's about .010" mouth clearance in most chambers with cases at spec dimensions. It's controlled by case headspace point to case mouth

 

[1stmarine]

I will assume you meant 'chambering' and I do not know what you mean by "I have done this for a long time". What have you been doing for a long time? I can find no mention of any smith or reloader that that measures a chamber with any gage except the go, no and beyond gage with one exception. And then there is the modifying of gages as in one gage does it all from go-gage length to infinity or a more practice length that would be .016" longer than a minimum length/full length sized case for the 30/06 chamber.

F. Guffey

ok. I am referring to the chambering process of making rifles and pistols and wilcats too. Sorry bout the typo. My auto-correct perhaps.

I am not trying to get into long arguments that do not go anywhere and often too long and even boring but really tried to understand the logic here.

You might not find any mention of any smith that chambers with any gauges other than a go, no-go and beyond but you also said
that you would measure and possibly return gauges of different sizes.

Instead of continuing in circles let me provide a couple of examples with actual measures:

A) The simpliest scenario. Lets even forget we are chambering a rifle. Lets say we buy a 308 rifle off the rack.
We give it a good cleaning and then we decide to check the headspace just to make sure is safe that is the most common reason.
We put the no-go gauge and it closes, ok. At this point we take another no-go gauge that is 2 thousands longer than the
the first one (lets say PTG 1.636 vs. Forster 1.634) and then it doesn't close. We use forster go gauge of 1.630" to verify and it closes.
Factory ammo and reloads chamber w/o problems. Everything is good and safe.

B) One is chambering a caliber. When checking headspace the chamber will not close on the largest no-go gauge.
I want this chamber to be most accurate it can be for my match ammo and reloads. I have to shorten the shoulder
in the tenon and thefore adjust the headspace. I will use the cutting tool to do 1 or 1/2 thousand increments and can
use a micrometer but at this point my gauges are the best way to verify. I will have to verify anyway after installing and
torquing the barrel to the action. Additionally I have a couple of dummy rounds FL sized from my set of dies. I will be using
these for tuning the headspace. At this point I cut, clean and test and get to the point where the case is snug yet the bolt
drops into battery. At this point I use a go gauge and it closes but it is sticky. So I decide to put a forster 1.631" that will give
me almost the same feedback. we are talking the bolt is closing but with friction. So now I take a forster go gauge that is
1.630 precisely and the bolt will close. Of course I also take the shortest no-go gauge that is the forster too and verify
the chamber doesn't close with that gauge. I torque the barrel and repeat the same process again with same results.
Everything is good and safe too. In addition I have the best possible chamber I can have with the rounds I have used
for head-spacing all fully supported as confirmed by the 2.631 gauge. My chamber is 2.631".

If I didn't have more than one gauge with different dimensions I would have to use alternative methods in both situations.
In the case of chambering having the brass is paramount as the rifle is headspaced with the rounds and not the gauges.
As I said several posts above the gauges are just a verification. The chamber is matched to the rounds and the rounds
to the chamber. The math adds up and fall within the expected tolerances.

These are the reasons people buy different brands of gauges with different measures or gunsmith sets.

This is a full set other member posted in a related thread a while back.
Similar subjects seem to repeat from time to time.

https://www.thehighroad.org/index.php?threads/making-dummy-rounds.711585/




Alternative measures for measuring the chamber and gauges will not provide more precision that the specified and often printed value in
the forster, PTG, mason, etc.. gauges. They use machines and processes most of us cannot compete with so IMO it doesn't make any sense
to verify them.

I also wonder what kind of explanation one can give to the manufacturer for the return.

 

[fguffey]

A) The simpliest scenario. Lets even forget we are chambering a rifle.

That is a good start because If I was cutting a chamber I would start with cutting it short; there is nothing like knowing the length of the chamber from the shoulder to the bolt face. As you know all reloaders size fired cases that are .002" shorter from the shoulder of the case to the case head than the chamber length from the shoulder to the bolt face.

I have tools, I do not covet tools, a box of head space gages is nice, if I found it necessary I would make them. I have at least two grinders that are used to make pilots, tapered gages, the old no/not go gages and the grinder grinds to length and grinds a shoulder, I can make one gage that measure the minimum length to infinity; I can make a gage that is too long, both gages can be used to measure the length of a chamber. I understand there is a big chance there is no cool factor.

Alternative measures for measuring the chamber and gauges will not provide more precision that the specified and often printed value in
the forster, PTG, mason, etc.. gauges. They use machines and processes most of us cannot compete with so IMO it doesn't make any sense
to verify them.

I ask if you do not believe it can be done tell me; that would save me time. No sense to verify? I have read on every forum members claiming the manufacturer must match when using shell holders and dies. Not for me; the shell holder deck height is .125", I measure the deck height of my shell holders, on occasions I get lucky when I find a shell holder with a different deck height, manufacturers charge more for shell holders with a different deck height.

it doesn't make any sense to verify them

The shell holder and die is designed to return the case to minimum length/full length. Meaning when the ram is raised and the case is sized there will not be a gap between the top of the shell holder and bottom of the die. A reloader can verify the die with a go-gage, it is a simple task; place the go gage into the die with the primer punch/sizer ball assemble removed. After placing the go gage into the die place the shell holder over the go gage and then measure the gap between the bottom of the die and top of the shell holder with a feeler gage. In the perfect world the gap will be .005" for the 30/06 family of cases. A reloader that can not verify the head space gage will have to assume the sizing die is cut correctly. I can not imagine a reloader not being capable of measuring the deck eight of a shell holder, I believe a reloader should have the ability to measure the length of a go-gage and I can not believe a reloader would allow someone to tell them it was not a necessary skill.

And then there are those that do not have the gages but have problems sizing a case that will not chamber. It is possible to have cases with more resistance to sizing than the press can overcome. Again, when the case is sized and returned to minimum length but when that does not happen and there is a gap between the top of the shell holder and bottom of the die the reloader can measure the gap with a feeler gage. I have made shop calls when smiths/reloaders have equipment that failed to return a case to minimum length. One smith had a gap of .017" between the top of the shell holder and bottom of the die and the ram could not move up any further. He has his A2 RCBS press in such a bind the top of the press had flexed .017",

They use machines and processes most of us cannot compete with so IMO

They have to start at the same place with a micrometer; they start measuring from zero.

F. Guffey