setting headspace during prefit barrel installation

a1b3rt

a1b3rt

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I have a small project going on recently.
I am building a blot action 308 based on Cadex R7 action. The barrel I'll use is a "remage" style prefit with custom thread to match the R7.
with all the necessary homework I've done I am still a little curious about if it is possible to set up the headspace WITHOUT removing both ejector and extractor from the bolt.
I know removing both when setting up the headspace is a well accepted "good practice", however, I still want to dig more about how to set up the headspace without removing them.
The go gauge and nogo gauge I got from Brownells both have a "cut" at the rim I think that means if I hand-guide them onto the bolt there should be no contact with the extractor at least. Yes the ejector will generate a little pressure to the gauge but will this pressure cause inaccurate headspace measurement?

Thanks!
Albert
 
A plunger ejector will affect the feel of the gauge as the bolt closes.
Generally speaking, a light touch is desired when using headspace gauges.

If the bolt closes on the GO with the ejector in lace, obviously the bolt will close on a cartridge.
When you use the NO GO gauge with the ejector in place, be careful. Compressing the ejector spring requires more effort than when the ejector has been removed. With the ejector in place the feel is different. Is the force you are applying compressing the spring or is the camming advantage built into the action forcing the bolt closed on a hardened steel gauge? If the bolt won't close on a NO GO with the ejector installed, obviously the headspace is not excessive. But it is a ham handed approach.

When I am breeching up a precision rifle, I like to just feel the GO gauge as the bolt closes. I then know I have minimum headspace. With the ejector in place, that delicate feel is gone.
 
I have done as you describe - had fed a rimmed gauge behind the extractor and then tested for headspace - but I have not tried that with a bolt with a plunger ejector - just on Mausers, Lee Enfields, M1917 and P14. If it were me, I would go as tiriaq and others recommend - using the gauges is not about forcing your bolt closed or not - is about feeling when or whether the gauge front touches - you feel that through the bolt handle - delicate - very light finger tip pressure.
 
Thank you BOTH! There is a video on youtube "**How to Install a Prefit Barrel** Preferred Barrel Blanks Headspace and Torque Barrel Nut Prefits" In that video, and also in many other prefit installation videos found online, people always screw the barrel in until it touches the gauge and stops, and then they would slightly back off the barrel a bit, so I guess IF I want to leave the ejector on the bolt when using go and nogo, I don't turn the barrel back but need to feel a solid-ish touch?
 
I'd back off the barrel slightly after bottoming out the ejector on the GO. Then be careful with the NO GO, making sure you are getting an accurate feel.
The camming on closing has a lot of power.
 
How difficult is it to remove the ejector on that Cadex? If it's like a Remington, its not that difficult. As a beginner, I would err on the side of caution, and remove the ejector to get the best possible feel.
 
Maybe helps to know that typically there is .004" difference between GO gauge and NOGO gauge - so is generally assumed that for new barrel installation, you want the headspace to be between those dimensions - as per above, is a thought that dead minimum might be more "precise", or have other advantages. So, screwing the barrel in until the chamber touches the GO gauge, then backing off "a bit", is so that you end up between GO and NOGO lengths. NOGO is not maximum length - can see on most SAAMI drawings that Maximum chamber is often .010" longer than Minimum - I believe to allow for wear, etc. But that GO / NOGO thing sets that "target" length for a new installation, usually. A "full" set of normal gauges is three - GO, NOGO and FIELD. If a bolt closes on FIELD gauge, it is longer than SAAMI standard. I can not find where SAAMI defines a NOGO gauge length - I suspect it might be a commercial construct to aid in new barrel installation. GO = minimum; FIELD= maximum. Or just get only a GO gauge - and cut discs from leaves of a feeler gauge set - can determine your exact headspace that way, as well, by placing a disc between the bolt face and the gauge.

Gauges are, well, "gauges", to measure against a standard. For example, I have not read why SAAMI decided to set shorter standards for 6.5x55 than did Sweden military. Sweden were making 6.5x55 ammo and rifles at least 40 years before SAAMI existed. So, was not uncommon for a brand new Swede rifle from Carl Gustaf armoury to close on a SAAMI FIELD gauge - was properly gauged for the gauges used by Sweden, but not for USA SAAMI. You will go pretty much nuts trying to make sense, if you have a Sweden GO gauge and a SAAMI FIELD gauge. The Regimental Swedish GO is longer than a SAAMI FIELD.

For the 308 Winchester in particular, from the 2015 SAAMI drawings, it calls out the headspace dimension for a chamber between 1.630" and 1.640" That will be the GO and the FIELD gauge. On the same page, for SAAMI compliant cartridges, shows case can be 1.634 -.007, so shortest SAAMI compliant cartridge could be 1.627" - so .003" shorter than a Minimum SAAMI chamber. These measurements are from that theoretical circle on the shoulder slope, where it measures .400".
 
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Potashminer said:
Maybe helps to know that typically there is .004" difference between GO gauge and NOGO gauge - so is generally assumed that for new barrel installation, you want the headspace to be between those dimensions - as per above, is a thought that dead minimum might be more "precise", or have other advantages. So, screwing the barrel in until the chamber touches the GO gauge, then backing off "a bit", is so that you end up between GO and NOGO lengths. NOGO is not maximum length - can see on most SAAMI drawings that Maximum chamber is often .010" longer than Minimum - I believe to allow for wear, etc. But that GO / NOGO thing sets that "target" length for a new installation, usually. A "full" set of normal gauges is three - GO, NOGO and FIELD. If a bolt closes on FIELD gauge, it is longer than SAAMI standard. I can not find where SAAMI defines a NOGO gauge length - I suspect it might be a commercial construct to aid in new barrel installation. GO = minimum; FIELD= maximum. Or just get only a GO gauge - and cut discs from leaves of a feeler gauge set - can determine your exact headspace that way, as well, by placing a disc between the bolt face and the gauge.

Gauges are, well, "gauges", to measure against a standard. For example, I have not read why SAAMI decided to set shorter standards for 6.5x55 than did Sweden military. Sweden were making 6.5x55 ammo and rifles at least 40 years before SAAMI existed. So, was not uncommon for a brand new Swede rifle from Carl Gustaf armoury to close on a SAAMI FIELD gauge - was properly gauged for the gauges used by Sweden, but not for USA SAAMI. You will go pretty much nuts trying to make sense, if you have a Sweden GO gauge and a SAAMI FIELD gauge. The Regimental Swedish GO is longer than a SAAMI FIELD.

For the 308 Winchester in particular, from the 2015 SAAMI drawings, it calls out the headspace dimension for a chamber between 1.630" and 1.640" That will be the GO and the FIELD gauge. On the same page, for SAAMI compliant cartridges, shows case can be 1.634 -.007, so shortest SAAMI compliant cartridge could be 1.627" - so .003" shorter than a Minimum SAAMI chamber. These measurements are from that theoretical circle on the shoulder slope, where it measures .400".
Click to expand...

this explains my questions so well! Thank you so much!
 
For years I have read warnings about being careful on closing the bolt on steel gauges... my experience has been that isn't worth a warning...

As Tiriag posted in #2 ... Ideally ones removes the plunger style ejector... then if you have the headspace set to absolute minimum you will barely feel the bolt close on the go gauge... right at the bottom of the bolt closing you will feel a little resistance... that resistance disappears if the gauge is removed... then you will find the bolt stops hard on the no go gauge... and really there is no way you can force it closed and no reason to attempt that.

As long as the bolt closes on a go gauge and not on a no go you are within accepted tolerances... but if you set it to minimum your brass will fire form with less stretching and longer life. Sometimes headspace set to minimum can be a problem with reloading and your sizing die may need an adjustment if it doesn't size a fired case enough.

If one is able to force the bolt closed over a steel go gauge you wont harm anything but the bolt and locking lugs will be under pressure and the headspace is set too tight. When you open the bolt the compressed bolt/lugs/etc will just spring back to where they should be. No damage done, the steel was not moved beyond it's elastic abilities.
 
Grizzlypeg said:
How difficult is it to remove the ejector on that Cadex? If it's like a Remington, its not that difficult. As a beginner, I would err on the side of caution, and remove the ejector to get the best possible feel.
Click to expand...

Exactly, even if you need to incur the cost of a special punch or jig. What are your eyes worth?
 
To continue about gauges and standards - so most gauges that are sold, at least that I see in North America, make reference that they meet SAAMI criteria. Nobody says that any military has to follow SAAMI standards - often many existed long before SAAMI did - 303 British, 30-06, etc. And, it is not SAAMI that sets any standard for 7.62 NATO or 5.56 NATO - I believe it is NATO that does so - it might or might not match up with SAAMI - maybe has the same or different minimum or maximum dimensions. And for sure, during wartime, militaries had "relaxed" standards, so that what Canada had for FIELD length in their 303 British in 1944, may not be the same dimension that they had in 1931. Sometimes, Britain, Canada and Australia had different military standards for the same 303 British cartridge. Again looking at the 2015 SAAMI document, they call out .064 as minimum and .071 as maximum headspace for 303 British - people will quote alternate numbers - which were likely correct at one time or other, and or at one country or other, especially in their military.

Much of Europe complies with C.I.P., which is similar to SAAMI - they set standards for their countries. For some cartridges, the two are not at all the same - a good example would be the European 8x57JS versus USA 8mm Mauser - many hundreds feet per second difference in velocity for the same weight bullet, due to the two different pressure standards that were set - both call out .323" diameter bullets. Unlike USA, however, when a country, like Germany, adopted C.I.P., that had the force of German law - there is no option, there, of producing a product that is not in compliance, and then selling that product to a consumer. In USA, there is no penalty for not complying with SAAMI - it is a voluntary standard. Some countries, like Sweden, adopted their own standards - often similar to C.I.P., but they control the details and specifications within the standard that they use, not C.I.P.
 
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