Head space on a barrel switch

If you look at the SAAMI drawings for rifle cartridges, you'll see all rimless cases that headspace on the shoulder have a specific diameter designated for the measurement. As described in my previous image, this number is 0.400" for .308 Win. For .30-06 it is 0.375". For the .223" it's 0.330", etc. The Stoney Point design (bought out by Hornady and sold now as the LNL gauge) has 0.330", 0.350", 0.375", 0.400", and 0.420" available as standard inserts, those being the most common sizes specified by SAAMI. Some, like 0.365" specified for the 6.5×55 Swede, are not among those, and you can buy a blank from Hornady with a 3/16" hole through it and bore that out and ream it to your desired diameter.

If you want to get an accurate absolute measurement from the LNL gauge, you have to calibrate to allow for the radius on the mouth of the hole. The way you do that is to measure a good quality headspace gauge of known length. Then just add the difference from your reading and the gauge length to all case measurements you make.

The trick with the above is to know the headspace gauge is good. I don't know what Forster's QC is like today. It may be improved over what it used to be, as modern CNC machining has done that for a lot of manufacturing. My only experience with their headspace guages is with an armorer's set for .308 Win that I bought back around 1990. This is a set of 8 gauges from 1.630" to 1.638" in 0.001" steps. The gauge in the kit marked 1.638" measures 0.001" shorter than the one marked 1.637" in either my Stoney Point gauge or in my .308 RCBS Precision Mic. The ones marked 1.633" and 1.634" measure to be the same length. In other words, there is at least 0.002" of error in some of them. The .308 Winchester GO gauge I have that Dave Manson made, on the other hand, I have been able to check with a height gauge and surface plate and precision bored sharp hole and found to be within half a thousandth. That's the limit of resolution on the two height gauges I own, so it could be closer or even dead on.

Since you already have the Forster GO gauge, I would find a gunsmith with any other brand and use your LNL gauge to compare the two. If your's is different, you may want to buy one from Manson. I'd also expect Pacific, JGS, or Clymer to be good. But if there's no significant difference between yours and his, the probability of both having the same exact error is small, so they are then likely both pretty close to their marked length.
 
Headspace on a barrel switch

Thanks again Unclenick! I appreciate your kindness to share your experience. There are no gunsmiths that advertise locally but we do have a Gander Mountain in town. I will see if their gunsmith will let me measure his gauge.
I just got off the phone with Jim Briggs at Northland Shooters Supply concerning a Criterion Bull barrel in 260 Rem. so I might get to see how this all works out soon.
Thanks again!
Bill Daniel
 
Criterion Bull barrel in 260 Rem.
Click to expand...

Dayum good choice...

I'm getting my (new to me) 7mm-.08 Savage to the range for the first time Sunday. Gonna see how the factory barrel shoots first, but if it doesn't get me sub-minute that's my choice... Criterion (Krieger) has a great rep for the price.

I'd like to re-barrel both our Savages to .260, to keep costs down I've been looking for barrels "in the white", since I paint them anyway and don't need blued, much less stainless. Can't find them unfinished, tho...

Good luck with it, let us know how it turns out.
 
Headspace on a barrel switch

Will do tobnpr! Of course I will have to see what's available after distribution of income to the grandchild fund, the refinnish the up stairs fund, the childrens perpetual education fund and apply the "you want to buy what" factor. But hopefully soon.
Thanks,
Bill Daniel
 
I do not use go, no or or beyond gages, If a chamber gage was necessary, I would make one, everyone else gets their gages from Mars, because they are so precision it is beyond the ability of humans to make one.

No one wonders how it is possible to avoid ‘the head space gage’ long ago I made tools that measured the length of a case from the head of the case to it’s shoulder, then I coheres-ed the press to size cases that would not chamber, then used a feeler gage to adjust the press to form cases in varying length, then went back to the home made tool to verify adjustments. I do not use Sinclair/Hornady’s tool, I do not find it necessary, nice but not necessary.

Then there is head space and what a reloader can do about it? There is nothing I can not do with head space, for me the easiest task is determining ‘how much’ or, determine the length of the chamber first, then size cases that will off set the head space, and I know all the old hands are tired of hearing about it, but, I have one rifle with .016 thousands head space, I shoot it with .002 thousands head space, I use 280 Remington cases to form 30/06 cases that have an added .014 thousands to the length of the case from the head of the case to it’s shoulder.

Again, there are M1917s with long chambers, some claim/blame a smith in Utah because of his methods and techniques, I can check head space on a M1917 with a field reject gage, that includes go-gage length, no-go gage length and the field reject gage length (in thousands), no way to get a free cup of coffee but I can also check head space on a 30/06 chamber with a 280 Remington Minimum length/full length sized case after I have checked the length with my home made tool.

F. Guffey
 
Headspace on a barrel switch

F. Guffey thanks. I appreciate your response. I don't understand it but I do appreciate it none the less.
Bill Daniel
 
“Why do you not set the head space on the go gauge only? AGI recommends using tape to give the head space 0.002 to 0.004 inch excess over the go gauge.
Thanks,

Bill Daniel”

“I appreciate your response. I don't understand it but I do appreciate it none the less”

No one has a responsibility and or is obligated to make an attempt to try to understand.

http://www.americangunsmith.com/

You mentioned AGI, on the outside chance there are some reading through this form that have no clue what AGI stands for and again (on the outside chance you are talking about American Gunsmithing Institute), I posted a link.

As to their recommendation to add tape to the rear of the gage to lengthen the gage, .002 to .004, makes no sense, the go-gage is longer from the head of the gage to the shoulder of the gage than the minimum length case, meaning if we are talking about a 30/06 a go-gage length chamber presents a head space of .005 to the minimum length/full length sized case. If we are talking about (for example) the 30/06, adding .004 thousands to the length of the gage when reaming the chamber, the added .004 would results in a chamber, when measured. would be a no go-gage length chamber.

Again, I do not use head space gages, I do not shoot head space gages. Wilson Barrel Co. provides instruction, what happens when a AGI educated smith receives a barrel and instruction from Wilson and finds Wilson gives two choices, neither agrees with the institute of gunsmithing.

The AGI also says check often, no one knows where the are or how far they have to go to finish the chamber, it is possible to know, in thousands, the length of the chamber even if it is a short chamber (and we all? know a go-gage will not chamber/allow the bolt to close in a short chamber unless it is the same length as a minimum length case), and I say there is no excuse for not knowing the length of the chamber from start to finish, they give the smith an excuse with their ‘qualifying statement “NO ONE KNOWS”, that makes me want to break into “WHO KNOWS WHAT EVIL LURKS IN THE MIND etc..), we all know the answer, the shadow do.

Thanks for asking?

F. Guffey
 
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forgive,

should be “neither agrees with with the institute of gunsmithing”

not: "neither aggregating with the institute of gunsmithing"

F. Guffey
 
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I really don't know what AGI is up to with the tape, either. I've never heard of doing that. My first speculation, mentioned earlier, is that they are aiming for the middle of the headspace range for feed reliability. The only other thought I had was regarding the caution Hatcher had about closing bolts on headspace gauges. He points out that many bolts are perfectly capable of camming hard enough to stretch the chamber several thousandths with a headspace gauge inside, rather than refusing to close. So perhaps AGI is also trying to make an allowance for somewhat ham fisted new practitioners. A little practice measuring with a micrometer gives you appreciation of the need for feather light contact in accurate measuring. You simply have to develop a feel for it. But I like my first speculation on AGI's purposes better.

BTW, the light touch is why one is normally advised to strip a bolt before trying to use a headspace gauge. Even if you have an ejector notch in the gauge, spring pressure from the cocking mechanism can interfere with how sensitively you can detect first contact between the gauge and chamber.

Mr. Guffey is correct that you can either get other chamber dimensions to deduce effective headspace from or you can ignore exact headspace if you are going to load only cases fireformed to your chamber and set back only as needed to function reliably. Just don't fire commercial or military loads in an undersized chamber, as that increases pressure. If in doubt, put a squib load together and fire it to see how the case length comes out.

Hatcher reported on some experiments where .30-06 headspace was intentionally extended 0.050" long with a special reamer, and it didn't damage the brass or fail to shoot well enough for military purposes. The standard new rounds going into the long chamber just headspaced on the extractor hook and blew their shoulders forward when they fired. Lots of wildcats have been made that way. The Ackley Improved approach is probably best known among those that will allow you to shoot the parent cartridges directly without first knocking the charge down or using some kind of blank load to form the cases. The only thing is, you then want to resize for your cases for that big chamber or the brass will thin out at the pressure ring and start giving you head separations in relatively few reloads. Also, accuracy won't be best if the case rattles too loosely in the chamber.

There are lots of ways to work out there. Ultimately, the main thing is to keep in mind what your objectives are and to work out how to get yourself there and prove to yourself that you've gotten there. Headspace gauges are a conventional approach and are also used in manufacturing to meet SAAMI specs, but it's worth noting that SAAMI is oriented toward manufacturing and that an individual with time and different tools and a bit of ingenuity can find lots of workarounds for conventional methods.
 
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Headspace on a barrel switch

Mr. Guffey, Unclenick and any others. This particular American Gunsmithing Institute video was for the Savage 110/10 rifle. Could the tape issue be related to the "floating" lugs on a Savage bolt. I noticed the same tape on the Go gauge advice on the Savage Shooters forum that was credited to Savage Inc. Whether it actually was or some one else who watched the same video as I did gave credit to the folks at Savage themselves.

Mr. Guffey on re-reading my post response to you I sounded like an ungreatfull smart a--. In reality I just don't know enough to keep up with your posts. I perceive that you are either a machinist by trade or have been working on guns for a long time. On the otherhand I only know- what I think I overheard from "some guy" who sounded like he knew about which he was talking, i.e. not much . In any event I appologize for the tone of my response.
Bill Daniel
 
Unclenick,Hatcher did not start out with his test to test extractors, he started out to determine a preconceived notion a case would come apart with excessive head space, his experiment was about deterring the amount of head space the case would tolerate. he was correct, a case fired in a chamber with .050 to .080 thousandths will suffer case head separation, Hatcher’s experiment failed because of the process of selection.

Hatcher was unaware the case shortened when fired in his new creation, the 30/06 Hatcher Modified, had he measured the length before and after and found the case did not shorten he would have know his experiment was working and all he had to do was advance the reamer to increase the length of the chamber, fire and then look for the bright ring around the case ahead of the case head.

F. Guffey
 
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Bill Daniel, forgive, I have short lists, my short list of people I will loan a book to has two names, Norm Hitzges and a former minister.

On the Internet, my short list of members on different forums that are world class is not that short, but, at the top is Unclenick, in your last post you showed more class than I have seen in a while, so I will add you to my list of members with class. That puts you in good company, never want to forget to tell William T. Watts how much he is appreciated.

F. Guffey
 
Thank you Mr. Guffey. May I return the compliment.


Bill,

I can still only speculate on what the tape objective is. If the GO gauge fits, so will an in-spec cartridge, and that's the goal. Increasing that headspace by two thousandths puts you in the middle of the SAAMI new chamber spec range for .308 Win (1.630"-1.634"), and that's probably not a bad strategy for a manufacturer of new guns, as it gives employees a couple of thousandths of error wiggle room either way. Thus, the gal who sets the barrels up could be a little heavy handed one day when she's mad at her husband and or a little light another day when she's thinking ahead to her sister's wedding, and the guns still come out within spec. Sometimes it's worth remembering that SAAMI is a manufacturer's association and not a custom gunsmithing association, and that the problems manufacturers have are often special to the manufacturing environment.
 
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