Have you ever measured more than one GO gauge for the same caliber?

[BoydAllen]

This came up recently. A friend did a barrel job, and then the fellow that it was done for could not close the bolt on his GO gauge. It turned out that the difference was probably under a thousandth, but steel does not compress well. The customer was just sure that gauges are all exactly the same. I assured him that anything that can be bought that inexpensively is probably not. What have you observed?

 

[shortgrass]

Everything has a working tolerance. No 2 items are exactly the same. If you can work to within 4 places to the right of the decimal point, repeatedly, you're doing something.

 

[DaveTooley]

I have several, like 4, 300 PRC gages dating back to 2007. None are the same. I think there was a thou and a half difference between them. Other than something to talk about it means nothing in practical terms.
Go +.001" eliminates a lot of phone calls.

 

[Cigarcop]

I’ve got two WSM gages that for the life of me I can’t measure any difference but I can tell you they don’t work well together!

 

[memilanuk]

There was a fair amount of discussion about this leading up to the last (2017) F-class World Championship. The fine folks at ICFRA didn't want to settle for just gauging fired cases to make sure that competitors (FTR) weren't using illegal chambers; they insisted on checking chambers with gauges. Oddly enough, they were as much (or more) concerned about people using *undersized* chambers - some freak-azoid paranoia about if some (international level competitor) were to 'accidentally' pick up a random piece of ammo off the ground and stick it in the chamber of their custom match rifle, it had to still be 'safe'

They ended up having a special run of gauges made to a specific set of dimensions, and all the various teams scrambled to get a set. Because they were a limited run, made to exacting tolerances, they were about 4-5x more expensive than normal.

I got my hands on one of the 'go' gauges for a limited time, and compared to my Forster .308 'National Match' set of gauges (every 0.001") they ended up being closer to somewhere between 1.631" and 1.632", vs. 1.630", IIRC.

 

[Roeder]

A friend of mine worked as a machinist at the Rock Island Arsenal for many years. They ground headspace gages for use at all the arsenals. They frequently did "first article" inspections on gages submitted for government contracts and almost never were able to accept the sample gages. Hence they ground gages at the arsenal. The standard was comparable to a gage block, something like 50 millionths or less. Most commercial gage drawings specify a tolerance of +.0005. I have had the experience of having another guy check a barrel I had fitted and found it tight on his gage whereas the bolt handle flopped on mine.

 

[Dusty Stevens]

None are the same even from the same mfr

 

[DaveTooley]

They can be but at what cost and what is the gain? Factory ammo goes boom and you adjust the FL die to match the chamber. Done deal.

 

[hoz53]

They can be but at what cost and what is the gain? Factory ammo goes boom and you adjust the FL die to match the chamber. Done deal.

I agree with that and wonder how long over spec the chamber can be before reduction of brass life from stretching on first firing. I think back to some chambers I’ve cut and had to Fix because I overdid it and they closed on a NO- GO. Prob only 001 or 002 over and wouldn’t have hurt anything since I’m using them for myself? Sorry if I hijacked your thread Boyd

 

[tobnpr]

Prob only 001 or 002 over and wouldn’t have hurt anything since I’m using them for myself?

I wouldn't worry about it based on one or two over "no go" provided you're doing minimal shoulder bump when resizing.

I do believe there's a limit to this...got into a "spirited" discussion on another forum recently where the OP said he was closing on a field gauge with room to spare still, and I told him it was unsafe. Quite a few jumped in and said it didn't matter based on minimal resizing as I just mentioned, but I didn't agree. When you reach the point of failing a field gauge there's a risk of the thinner brass above the casehead being unsupported and separating.

JMO, YMMV.

 

[Dgd6mm]

I wouldn't worry about it based on one or two over "no go" provided you're doing minimal shoulder bump when resizing.

I do believe there's a limit to this...got into a "spirited" discussion on another forum recently where the OP said he was closing on a field gauge with room to spare still, and I told him it was unsafe. Quite a few jumped in and said it didn't matter based on minimal resizing as I just mentioned, but I didn't agree. When you reach the point of failing a field gauge there's a risk of the thinner brass above the casehead being unsupported and separating.

JMO, YMMV.

This is definitely a fact. People that argue have never sectioned a piece of brass. How do they say it? Ignorance is bliss, or in our cass catastrophic.

 

[Dusty Stevens]

I wouldn't worry about it based on one or two over "no go" provided you're doing minimal shoulder bump when resizing.

I do believe there's a limit to this...got into a "spirited" discussion on another forum recently where the OP said he was closing on a field gauge with room to spare still, and I told him it was unsafe. Quite a few jumped in and said it didn't matter based on minimal resizing as I just mentioned, but I didn't agree. When you reach the point of failing a field gauge there's a risk of the thinner brass above the casehead being unsupported and separating.

JMO, YMMV.

Im not arguing with you for sure because im a very staunch advocate of using gages to make a chamber per design, but you said a longer chamber leaves more casehead being unsupported but wouldnt the clearance between the bolt and counterbore remain the same no matter how deep you run the reamer in?

 

[Ksracer]

Im not arguing with you for sure because im a very staunch advocate of using gages to make a chamber per design, but you said a longer chamber leaves more casehead being unsupported but wouldnt the clearance between the bolt and counterbore remain the same no matter how deep you run the reamer in?

Depends on if it's a shoulder barrel that simply had the reamer run in to deep but has the rest of the features in the correct location. Or if it's a nut type barrel that wasn't screwed in deep enough, leaving a gap between the bolt and counter bore also.

 

[DaveTooley]

Im not arguing with you for sure because im a very staunch advocate of using gages to make a chamber per design, but you said a longer chamber leaves more casehead being unsupported but wouldnt the clearance between the bolt and counterbore remain the same no matter how deep you run the reamer in?

Exactly.
I can't list all the wildcats I've made that required fire forming. To include moving the shoulder forward.

 

[hoz53]

Im not arguing with you for sure because im a very staunch advocate of using gages to make a chamber per design, but you said a longer chamber leaves more casehead being unsupported but wouldnt the clearance between the bolt and counterbore remain the same no matter how deep you run the reamer in?

yes what youre describing is true but tob said " the brass in front of the casehead" (not the casehead stretching ) to much which does happen if the chamber is to long right?

 

[Dusty Stevens]

yes what youre describing is true but tob said " the brass in front of the casehead" (not the casehead stretching ) to much which does happen if the chamber is to long right?

No he said the thinner brass in front of the casehead being unsupported. If he meant stretching then yes

 

[BoydAllen]

Another variable that comes into play, when dealing with installed, torqued barrels is the amount that headspace is changed from hand tight, to fully torqued. I have heard that the difference can run somewhere around .001 to .0015 depending on how much the barrel is tightened. Comments? Experiences?

 

[Dusty Stevens]

Another variable that comes into play, when dealing with installed, torqued barrels is the amount that headspace is changed from hand tight, to fully torqued. I have heard that the difference can run somewhere around .001 to .0015 depending on how much the barrel is tightened. Comments? Experiences?

Exactly true and gets worse according to action/tenon face quality and torque. If you take a barrel off that a gunsmith installed and its not gorilla tight but you put it back on that way, dont bother the gunsmith.

 

[memilanuk]

Another variable that comes into play, when dealing with installed, torqued barrels is the amount that headspace is changed from hand tight, to fully torqued. I have heard that the difference can run somewhere around .001 to .0015 depending on how much the barrel is tightened. Comments? Experiences?

Pretty common in the Savage world to spin the (pre-fit) barrel down hand tight on a GO gauge, then snug it up with the barrel nut wrench to take up any slack in the threads. I've tested/checked this a number of times - with a stripped bolt, if I snug the barrel by hand against the headspace gauge, I can't easily open the bolt. Put the wrench on it and tighten the barrel nut, and the same bolt will open easily, and the gauge will pop right out. Later, playing with a set of Forster National Match gauges for .308 Win (0.001 increments from 1.630" on up), confirmed it to be somewhere between 1-2 thou.

 

[DaveTooley]

Another variable that comes into play, when dealing with installed, torqued barrels is the amount that headspace is changed from hand tight, to fully torqued. I have heard that the difference can run somewhere around .001 to .0015 depending on how much the barrel is tightened. Comments? Experiences?

I probably saw that early on in my career but I don't see that any more. If the shoulders on the barrel and action are clean, the threads fit properly and both have a good finish I don't see how anything can change more than a few tenths. I don't see here.