This is why I have trust issues

[6Creed73]

SAAMI is not a spec, it is a tolerance. Are both within that tolerance? If so, ok. We all should be adjusting our dies to match our chambers and not the gauge anyway.

Yes, I know SAAMI is a tolerance. This is a go gauge which is supposed to represent the absolute minium of that tolerance. There is also a gauge that represents the maximum of that tolerance...everything in between is the tolerance range.

 

[gunsandgunsmithing]

In case I wasn't clear think about this...the hs guage can't have exactly the same shoulder angle as what the cartridge nominally calls for. I looked at a couple of reamer prints and they both show a +/- 1/4° tolerance for the shoulder angle of the reamer itself. Think about that for a minute and how it relates to this subject.

 

[jds holler]

We need to get ahold of Guffey to settle this. jd

 

[6Creed73]

In case I wasn't clear think about this...the hs guage can't have exactly the same shoulder angle as what the cartridge nominally calls for. I looked at a couple of reamer prints and they both show a +/- 1/4° tolerance for the shoulder angle of the reamer itself. Think about that for a minute and how it relates to this subject.

I think this is exactly the reason for the difference.

 

[hogpatrol]

Perfection is the enemy of good enough. YMMV.

 

[Walt Krafft]

It has been standard practice for years to always use headspace gages from the same manufacturer for the reason you are finding. There are tolerances and allowable differences.

 

[DShortt]

It is an interesting situation that the datum line creates. On one hand it's very consistent. On the other hand the very nature of a datum line on an angle or cone if you prefer is going to be difficult at best to match perfectly.

I think if we just remember that a headspace gauge, no matter a GO or NO GO is simply a reference tool and not get obsessed with perfection it's clear that there isn't a big problem here. It's a system that works fine if there's a clear understanding of just what the measurement is.

 

[One Eye Pete]

The final arbiter is your rifle chamber. Assuming you are shooting a bolt action, remove the firing pin assembly and ejector. Then size a case down 0.001 at a time until the bolt just barely falls freely. Measure this case with both gauges. Even if the measurements still differ by .002 they will give you the correct headspace measurement for your rifle. If you want a slightly looser headspace just add .001 to either measurement. When loading for accuracy headspace gauges are relative, you can’t always translate a measurement taken on one gauge to another. If you think this is bad trying to measure bullet seating depth with two different gauges can be even worse, and even your rifle chamber will change as the throat wears.

 

[Ledd Slinger]

Assuming you have a lathe, make your own HS gauges matched to reamers and it won't be an issue. But honestly, I don't really see an issue when considering SAAMI. Those specs are all over the place with different manufacturers rifles and ammo so who cares.

 

[Will Henry]

I would be curious to know if the gauge being used to measure the HS gauge was the correct diameter for the datum line specified by SAAMI. If not, given that there is an acceptable tolerance for shoulder angle, there could be some difference showing up from that. Since there is always going to be some tolerance in all measurements, one can only do his best with what is at hand.
If, for instance, the datum diameter for a given cartridge is .375", then you need a gauge which measures at precisely .375" in order to get a valid measurement. Otherwise, you will get a comparative measurement, but not in the right place.
If I want to make a gauge to a precise datum measurement, I will bore a hole which is as close to perfect as I can make it to gauge the gauge (let's call it .375"). Then I will make the gauge with a slightly shallower shoulder angle behind my datum point and slightly sharper ahead of it. Contact ahead of and behind the datum line will be minimal. In fact, it's not a bad idea to radius the contact line. Then, using the datum gauge, I will establish a front surface .125 ahead of the datum line on the HS gauge. Then I face off the back of the HS gauge to the specified HS measurement (to the datum line), plus .125", and Bob's your uncle. With a larger contact surface on the shoulder, any variation in shoulder on the gauge or in the chamber, will give an erroneous reading.
In the scheme of things, it doesn't matter a whole bunch because everything we are doing is comparative rather than definite. By the way, a case which measures .005 longer than minimum should be almost impossible to chamber in a strong, front locking action. WH

 

[Ledd Slinger]

I can't count how many barrels I've had made up by only using 3 pieces of brass with shimmed shoulders as a headpsace gauge. Never an issue. I've maybe owned 1 hs gauge in my life when i first started in but quickly discovered they aren't needed at all. Better to set it up on the brass being used in the rifle than some rough SAAMI spec gauge if you ask me.

 

[jds holler]

I think Guffey was an old codger, who knew his way around old rifles, and had developed his own methods for figuring out head space in ways that worked for him.

He wasn't always right, but he wasn't always wrong either. I've known guys pretty much like him who were tough as a badger, stubborn as a mule, and didn't care if you liked him or not. I'll bet a few of us miss his posts -- drama and all. jd

 

[6Creed73]

The final arbiter is your rifle chamber. Assuming you are shooting a bolt action, remove the firing pin assembly and ejector. Then size a case down 0.001 at a time until the bolt just barely falls freely. Measure this case with both gauges. Even if the measurements still differ by .002 they will give you the correct headspace measurement for your rifle. If you want a slightly looser headspace just add .001 to either measurement. When loading for accuracy headspace gauges are relative, you can’t always translate a measurement taken on one gauge to another. If you think this is bad trying to measure bullet seating depth with two different gauges can be even worse, and even your rifle chamber will change as the throat wears.

I already know at what point my rifle will start to get a heavy bolt. And that's what I use the indicator for, it's way faster. I've already done the work to determine the exact measurement in comparison to the headspace gauge. So I "zero" the indicator to the headspace gauge, and I know if I put a fired case in and it's .005 more than the headspace gauge then it's time to bump the shoulder .002. It's fast and repeatable.

 

[Ledd Slinger]

I think Guffey was an old codger, who knew his way around old rifles, and had developed his own methods for figuring out head space in ways that worked for him.

He wasn't always right, but he wasn't always wrong either. I've known guys pretty much like him who were tough as a badger, stubborn as a mule, and didn't care if you liked him or not. I'll bet a few of us miss his posts -- drama and all. jd

To me, the way Guffey did things was the equivalent of common core math. There's the fast, efficient, and correct way of doing things, then there was Guffey. He'd get there eventually, but he always took the longest and roughest road. Lol!

 

[6Creed73]

I can't count how many barrels I've had made up by only using 3 pieces of brass with shimmed shoulders as a headpsace gauge. Never an issue. I've maybe owned 1 hs gauge in my life when i first started in but quickly discovered they aren't needed at all. Better to set it up on the brass being used in the rifle than some rough SAAMI spec gauge if you ask me.

I don't use it to verify a chamber, I only use it as a comparator, basically a consistent starting point for sorting brass.

 

[gambleone]

I miss ole Guff & liked to read his posts, or try to.

 

[Fast14riot]

I think Guffey was an old codger, who knew his way around old rifles, and had developed his own methods for figuring out head space in ways that worked for him.

He wasn't always right, but he wasn't always wrong either. I've known guys pretty much like him who were tough as a badger, stubborn as a mule, and didn't care if you liked him or not. I'll bet a few of us miss his posts -- drama and all. jd

Guffey was the self proclaimed only person who knew what was and how to measure with a datum. Dont get him started on "bumping shoulders" because even advanced theoretical physicists didn't understand that it couldn't be done with brass cartridges.

He wasn't always wrong, and had some novel ideas, but boy he sure knew how to make 2+2=5, lol!

HS Guage is simply to make sure your chamber is within SAAMI tolerance and safe to shoot factory ammo. Personally I couldn't care less, last I checked my dies are adjustable. Minimum spec vs .004" (or whatever less than 0.010") longer than minimum is fine and I'm going to make sure my brass is sized appropriately.

 

[dellet]

Just a thought

The Forster is not off by .002”.

Both are off +/- .001” or less.

 

[ebb]

With the news media, government, BOTH political parties and social justice warriors taking such liberties with the truth, how could this tiny problem with headspace gauges even be a blip on your radar?

 

[JSH]

SAMMI spec, what parameters are they working with as far as + and -?
The tolerances have to be so much.
I mean one guys golden load for said caliber, may well not work in another’s rigs even if everything was the same. Scale variances could be off enough, even if they both read zero.