Headspace Gauges

Don Myers · October 20, 2001, 03:34 PM

I have a few questions about the headspace gauges. I would appreciate any help any of you can give me.

I understand that a 30-06 gauge will work on all 30-06 calibers. Whether or not one gun is an M1 Garand and another one is a 1903 A3 or a Remington sporting rifle doesn't matter. Is that correct?

How do you know whether or not the bolt is actually closed on an M1 Garand or other semi-auto rifle when you use the gauge? On a bolt action, the bolt has to turn all the way down. That I understand.

Do I need a Go Gauge, a No Go Gauge, and also a field gauge?

I am quessing that I will need about 4 or 5 different sets at the moment. I want to make sure that I am getting what I need. I have Lee Enfields 303 and .308, FN .308, SKSs and MAK 90s in 7.62 X 39MM, M1 Garands in 30-06 and other 30-06s, Ruger .223s and even a MAK 90 .223. My rifle collection is building up. I have not checked the headspacing on any of them.

Thanks for any help you can give me.

George Stringer · October 21, 2001, 07:32 AM

Don, that's correct. Headspace gages apply to calibers; not specific firearm types.

Just like a bolt action, it will be obvious if the bolt doesn't close all the way.

You shouldn't need a field gage. I don't think you need a field gage. There are folks who consider a rifle safe if it won't close on a field gage and it may be but I'm not one of them. I don't own a field gage in any caliber. If the bolt closes on a no-go then you want to correct the headspace. As your collection of calibers increases you'll find that some headspace gages work with more than one caliber. For instance the 30-06 is used for the 25-06 and several others. The .308 is also used for the .243. Etc. George

JNewell · October 21, 2001, 01:32 PM

My take on this: if you are not rebarrelling or rechambering rifles, or buying rifles that others -- other than the factory or a military depot or armory -- have rebarrelled or rechambered, you don't need a go gage. There are almost no circumstances under which headspace will shrink in use.

If you are buying used -- usually really used, or really old -- rifles, I would suggest having a no go gage. This will not tell you whether or not the rifle can be safely fired -- it may be safe to shoot, depending on circumstances if it will chamber the no go gage, but at least it's a yellow light. It tells you that the rifle may need further attention and may cost you some additional money. Of course, for a rifle purchased for collection purposes only and not to shoot, this wouldn't matter.

I agree with George on the field gage. I would be very careful shooting a rifle that flunked the no go but passed the field gage, and I wouldn't fire a rifle that flunked the field gage at all. One of the issues with the zone between no go and field gages is that a military rifle is often designed to be produced and used with greater headspace and a larger diamter chamber than a civilian rifle would be, but the brass that it's designed to be used with has more brass in the case head and lower walls. Used as a system, they are safe together, as well as being reliable. Used with thinner commercial brass, however, it may not be safe to fire. You don't really know, but who wants to find out the hard way? I take no go gages in calibers of interest with me to gun shows, and pass on rifles that swallow the no go gage. BTW, of course, always ask the vendor first!

Don Myers · October 21, 2001, 04:37 PM

JNewell
Well, I bought an M1 Garand parts kit and a new Springfield receiver. I had the local gunsmith put together the rifle for me. In this case, I think I might want all three gauges: Go, No Go, and Field. For the other calibers, I am thinking that the Go and No Go gauges would suffice. What do you think? thanks. Don

Doctari · October 21, 2001, 07:44 PM

Remember you must check headspace on these semi auto rifles with a stripped bolt. Clean and degrease the chamber and gauge. Slide the gauge into the chamber. Gently insert the stripped bolt into the reciever so it slides freely on the rails. Slide it forward and as it nears the chamber it will begin to rotate into battery. Gently push the bolt locking lug down with pinky finger tip pressure. The lug should contact the rail with a GO gauge. It should NOT contact the rail with a NO GO gauge. You don't really need a field gauge unless you feel brave.

I have a M1917 that almost swallows a field gauge. Hey George ever rebarreled any M1917 Enfields?

Bolt action guns headspace the same way. I always strip these bolts as well.

Good luck and safe shooting,

Mike

George Stringer · October 22, 2001, 08:50 AM

Mike, yeah. I have one in the shop now as a matter of fact. I should be testing your Whelen tomorrow if I can get out of here and to the range. Your "correct" front sight blade is supposed to be here today. George

James K · October 22, 2001, 03:06 PM

On any semi-auto rifle, always disconnect the op rod or whatever has the recoil spring before checking headspace. Otherwise the spring force can cause false readings or even ruin the gauge.

Jim

JNewell · October 22, 2001, 08:01 PM

Actually, Jim, I thought the problem was usually that the gage was so danged hard that they could damage the chamber? Could be mis-remembering.

Don, I still don't think you need the field gage. The rifle has been newly rebarrelled, so you should be able to determine whether it's good to go (pardon the pun) with just the go and no go gages.

On the go gage for others, if the barrel is either original or a factory or depot job, you concern would almost always be with too much headspace (as a result of wear), rather than too little.

Don't misunderstand me -- too little headspace can be just as dangerous as too much; maybe more (or at least more often) dangerous. It's just that all rifles are subject to increasing headspace; the only time you need a go gage is to verify a replacement barrel. (Note that you cannot check for minimum headspace with a cartridge, since brass stretches when the cartridge is fired, and the brass needs a little room in the chamber to expand into.)

James K · October 22, 2001, 09:58 PM

Hi, guys,

JNewell is correct in that the hard gauge can damage the rifle, but if the bolt of, say, an M1 is released and the gauge driven into the edge of the chamber or receiver, the gauge can also be chipped or dented. Anyway, never use a gauge of any kind in a semi auto rifle without removing the source of spring tension.

There seems to be a sort of idea that the GO/NOGO gauges are definitive and that a field gauge is an emergency, quick and dirty test that, if failed means the rifle is immediately dangerous. Not quite. Let's see just what headspace measures for a caliber that headspaces on the shoulder or case mouth.

In the manufacture of both guns and ammunition, there are tolerances involved. These are sometimes seen in loading manuals as +/- figures on cartridge illustrations.

So cartridges can vary, as can rifle chambers, whose allowable dimensions are also given as +/- figures.

When a rifle is being manufactured or rebarrelled, a GO gauge is used to make sure that the chamber is long enough to accept the longest case allowed in the cartridge specifications. We don't want a gun to jam just because some ammo falls into the outer edge of the tolerance.

A NO GO gauge is based on the shortest cartridge allowable under the specifications, plus a safety factor based on the amount a case can be allowed to stretch. We don't want a short case to stretch far enough to separate.

Those are fine at the factory or the gunsmith's shop. But rifle headspace increases with shooting (though not nearly as much as some folks here seem to think). That is where the field gauge comes in. ("Field" in this instance simply means anything outside the factory; it does not mean in a foxhole.) It is designed to test for an approaching dangerous condition with the SHORTEST cartridge allowable. Medium or long cartridges may still work just fine in a rifle that closed on ("failed with") the field gauge.

A rifle that accepts a field gauge should be considered a candidate for rebarrelling if it is going to be fired a lot. It does not mean that the rifle will blow up, or even that cases will stretch. It is a warning sign, a "yellow light", not a sign of immediate danger.

What are the causes of increasing headspace? When a cartridge thrusts back against the bolt face, the bolt lugs meet the bolt lug seats in the receiver. Both lugs and seats are compressed slightly. Plus the normal operation of the bolt wears both lugs and seats. In a well made rifle, it will take many thousands of rounds for this to become a problem. People who check headspace every ten rounds (as one poster said he did) are simply being silly.

What are the results of firing a rifle with excess headspace? Usually nothing. But when a cartridge fires, its thinner front walls grip the chamber walls and its back end will push back until or unless it meets a solid resistance. If the distance of the movement is very great, this can cause case stretching. If the distance of movement becomes too great, the case head may actually separate from the front of the case and let high pressure gas loose in the action. This is not good, though it rarely causes injury to the shooter.

Once headspace is excessive, the case head is not sufficiently supported at the rear. Stretching of a case in these circumstances has nothing to do with the shape of the barrel or type of bolt face. But if headspace is extremely excessive, the case can come back far enough that the sidewalls are not properly supported at the sides, and the sidewalls can blow out, again with unpleasant consequences.

It takes very excessive headspace for this to happen; I have seen one case that was really bad, and that was a case where a home gunsmith rebarrelled a rifle to a longer cartridge and ground almost 1/4 inch off the rear of the locking lugs so he could get the cartridge in the chamber. Incredibly, the rifle worked with two rounds before the third let go; all were extreme overloads since he also didn't think powder numbers really mattered.

HTH

Jim

October 20, 2001, 03:34 PM	#1
Don Myers Junior Member Join Date: October 20, 2001 Posts: 2	Headspace Gauges I have a few questions about the headspace gauges. I would appreciate any help any of you can give me. I understand that a 30-06 gauge will work on all 30-06 calibers. Whether or not one gun is an M1 Garand and another one is a 1903 A3 or a Remington sporting rifle doesn't matter. Is that correct? How do you know whether or not the bolt is actually closed on an M1 Garand or other semi-auto rifle when you use the gauge? On a bolt action, the bolt has to turn all the way down. That I understand. Do I need a Go Gauge, a No Go Gauge, and also a field gauge? I am quessing that I will need about 4 or 5 different sets at the moment. I want to make sure that I am getting what I need. I have Lee Enfields 303 and .308, FN .308, SKSs and MAK 90s in 7.62 X 39MM, M1 Garands in 30-06 and other 30-06s, Ruger .223s and even a MAK 90 .223. My rifle collection is building up. I have not checked the headspacing on any of them. Thanks for any help you can give me.

October 21, 2001, 04:37 PM	#4
Don Myers Junior Member Join Date: October 20, 2001 Posts: 2	Gauges JNewell Well, I bought an M1 Garand parts kit and a new Springfield receiver. I had the local gunsmith put together the rifle for me. In this case, I think I might want all three gauges: Go, No Go, and Field. For the other calibers, I am thinking that the Go and No Go gauges would suffice. What do you think? thanks. Don

October 21, 2001, 07:44 PM	#5
Doctari Member Join Date: March 27, 1999 Location: Lansing, MI Posts: 86	Garand Headspace Remember you must check headspace on these semi auto rifles with a stripped bolt. Clean and degrease the chamber and gauge. Slide the gauge into the chamber. Gently insert the stripped bolt into the reciever so it slides freely on the rails. Slide it forward and as it nears the chamber it will begin to rotate into battery. Gently push the bolt locking lug down with pinky finger tip pressure. The lug should contact the rail with a GO gauge. It should NOT contact the rail with a NO GO gauge. You don't really need a field gauge unless you feel brave. I have a M1917 that almost swallows a field gauge. Hey George ever rebarreled any M1917 Enfields? Bolt action guns headspace the same way. I always strip these bolts as well. Good luck and safe shooting, Mike __________________ Doctari is Doc on Safari

October 22, 2001, 09:58 PM	#9
James K Member In Memoriam Join Date: March 17, 1999 Posts: 24,383	Headspace (Long) Hi, guys, JNewell is correct in that the hard gauge can damage the rifle, but if the bolt of, say, an M1 is released and the gauge driven into the edge of the chamber or receiver, the gauge can also be chipped or dented. Anyway, never use a gauge of any kind in a semi auto rifle without removing the source of spring tension. There seems to be a sort of idea that the GO/NOGO gauges are definitive and that a field gauge is an emergency, quick and dirty test that, if failed means the rifle is immediately dangerous. Not quite. Let's see just what headspace measures for a caliber that headspaces on the shoulder or case mouth. In the manufacture of both guns and ammunition, there are tolerances involved. These are sometimes seen in loading manuals as +/- figures on cartridge illustrations. So cartridges can vary, as can rifle chambers, whose allowable dimensions are also given as +/- figures. When a rifle is being manufactured or rebarrelled, a GO gauge is used to make sure that the chamber is long enough to accept the longest case allowed in the cartridge specifications. We don't want a gun to jam just because some ammo falls into the outer edge of the tolerance. A NO GO gauge is based on the shortest cartridge allowable under the specifications, plus a safety factor based on the amount a case can be allowed to stretch. We don't want a short case to stretch far enough to separate. Those are fine at the factory or the gunsmith's shop. But rifle headspace increases with shooting (though not nearly as much as some folks here seem to think). That is where the field gauge comes in. ("Field" in this instance simply means anything outside the factory; it does not mean in a foxhole.) It is designed to test for an approaching dangerous condition with the SHORTEST cartridge allowable. Medium or long cartridges may still work just fine in a rifle that closed on ("failed with") the field gauge. A rifle that accepts a field gauge should be considered a candidate for rebarrelling if it is going to be fired a lot. It does not mean that the rifle will blow up, or even that cases will stretch. It is a warning sign, a "yellow light", not a sign of immediate danger. What are the causes of increasing headspace? When a cartridge thrusts back against the bolt face, the bolt lugs meet the bolt lug seats in the receiver. Both lugs and seats are compressed slightly. Plus the normal operation of the bolt wears both lugs and seats. In a well made rifle, it will take many thousands of rounds for this to become a problem. People who check headspace every ten rounds (as one poster said he did) are simply being silly. What are the results of firing a rifle with excess headspace? Usually nothing. But when a cartridge fires, its thinner front walls grip the chamber walls and its back end will push back until or unless it meets a solid resistance. If the distance of the movement is very great, this can cause case stretching. If the distance of movement becomes too great, the case head may actually separate from the front of the case and let high pressure gas loose in the action. This is not good, though it rarely causes injury to the shooter. Once headspace is excessive, the case head is not sufficiently supported at the rear. Stretching of a case in these circumstances has nothing to do with the shape of the barrel or type of bolt face. But if headspace is extremely excessive, the case can come back far enough that the sidewalls are not properly supported at the sides, and the sidewalls can blow out, again with unpleasant consequences. It takes very excessive headspace for this to happen; I have seen one case that was really bad, and that was a case where a home gunsmith rebarrelled a rifle to a longer cartridge and ground almost 1/4 inch off the rear of the locking lugs so he could get the cartridge in the chamber. Incredibly, the rifle worked with two rounds before the third let go; all were extreme overloads since he also didn't think powder numbers really mattered. HTH Jim

October 21, 2001, 07:32 AM	#2
George Stringer Staff Alumnus Join Date: October 12, 1998 Location: Earlington KY Posts: 2,299	Don, that's correct. Headspace gages apply to calibers; not specific firearm types. Just like a bolt action, it will be obvious if the bolt doesn't close all the way. You shouldn't need a field gage. I don't think you need a field gage. There are folks who consider a rifle safe if it won't close on a field gage and it may be but I'm not one of them. I don't own a field gage in any caliber. If the bolt closes on a no-go then you want to correct the headspace. As your collection of calibers increases you'll find that some headspace gages work with more than one caliber. For instance the 30-06 is used for the 25-06 and several others. The .308 is also used for the .243. Etc. George

October 21, 2001, 01:32 PM	#3
JNewell Senior Member Join Date: March 12, 2000 Posts: 1,092	My take on this: if you are not rebarrelling or rechambering rifles, or buying rifles that others -- other than the factory or a military depot or armory -- have rebarrelled or rechambered, you don't need a go gage. There are almost no circumstances under which headspace will shrink in use. If you are buying used -- usually really used, or really old -- rifles, I would suggest having a no go gage. This will not tell you whether or not the rifle can be safely fired -- it may be safe to shoot, depending on circumstances if it will chamber the no go gage, but at least it's a yellow light. It tells you that the rifle may need further attention and may cost you some additional money. Of course, for a rifle purchased for collection purposes only and not to shoot, this wouldn't matter. I agree with George on the field gage. I would be very careful shooting a rifle that flunked the no go but passed the field gage, and I wouldn't fire a rifle that flunked the field gage at all. One of the issues with the zone between no go and field gages is that a military rifle is often designed to be produced and used with greater headspace and a larger diamter chamber than a civilian rifle would be, but the brass that it's designed to be used with has more brass in the case head and lower walls. Used as a system, they are safe together, as well as being reliable. Used with thinner commercial brass, however, it may not be safe to fire. You don't really know, but who wants to find out the hard way? I take no go gages in calibers of interest with me to gun shows, and pass on rifles that swallow the no go gage. BTW, of course, always ask the vendor first!

October 22, 2001, 08:50 AM	#6
George Stringer Staff Alumnus Join Date: October 12, 1998 Location: Earlington KY Posts: 2,299	Mike, yeah. I have one in the shop now as a matter of fact. I should be testing your Whelen tomorrow if I can get out of here and to the range. Your "correct" front sight blade is supposed to be here today. George

October 22, 2001, 03:06 PM	#7
James K Member In Memoriam Join Date: March 17, 1999 Posts: 24,383	On any semi-auto rifle, always disconnect the op rod or whatever has the recoil spring before checking headspace. Otherwise the spring force can cause false readings or even ruin the gauge. Jim

October 22, 2001, 08:01 PM	#8
JNewell Senior Member Join Date: March 12, 2000 Posts: 1,092	Actually, Jim, I thought the problem was usually that the gage was so danged hard that they could damage the chamber? Could be mis-remembering. Don, I still don't think you need the field gage. The rifle has been newly rebarrelled, so you should be able to determine whether it's good to go (pardon the pun) with just the go and no go gages. On the go gage for others, if the barrel is either original or a factory or depot job, you concern would almost always be with too much headspace (as a result of wear), rather than too little. Don't misunderstand me -- too little headspace can be just as dangerous as too much; maybe more (or at least more often) dangerous. It's just that all rifles are subject to increasing headspace; the only time you need a go gage is to verify a replacement barrel. (Note that you cannot check for minimum headspace with a cartridge, since brass stretches when the cartridge is fired, and the brass needs a little room in the chamber to expand into.)