Headspace checking - general statement?

[dmftoy1]

Would it be accurate to say that if you're NOT putting on a new barrel, NOT cutting a chamber, and only interested in checking whether a gun is safe to shoot or not, that all you really need is a "no go" gauge?

I'm sure I'm being ignorant here, but it seems to me that if you properly check with the no-go gauge and the bolt won't close AND the gun will easily camber factory ammo . . .that you're good to go.

Any and all advice appreciated.

(I just picked up a couple of cheap mil-surps at the gun show this weekend and I'm trying to avoid spending $44 per caliber to check them . ..$22 I don't mind so much. )

Have a good one,
Dave

 

[Bwana John]

Would it be accurate to say that if you're NOT putting on a new barrel, NOT cutting a chamber, and only interested in checking whether a gun is safe to shoot or not, that all you really need is a "no go" gauge?

No, what you need is a "FIELD" gauge.

GO/NO-GO is for building the rifle, FIELD is for "excessive" headspace.

I have found that most older mil-surps will swallow a NO GO gauge.

 

[dmftoy1]

Thanks! I didn't understand that there was a distinction between no-go and field. I assumed they were the same thing. So a "field" gauge is typically slightly longer than a no-go?

Thanks for the education.

Regards,
Dave

 

[Jim K]

Headspace (long)

Even failure to pass a Field Gauge test does not mean the rifle can't be fired, though there will be a risk. If you KNOW that the rifle had previously checked out OK and just now failed the Field Gauge, you can continue to use it up to a point. In that situation, failure of the Field Gauge test is like seeing the wear marks on your tires. You don't park the car and never drive it again - you do look in the paper for tire sales.

But if you don't know by how much the Field Gauge test failed, then you take some risk in firing the rifle. Paper shims on the case head or bolt face can determine how bad the situation is.

Contrary to what has been written, excess headspace is NOT caused by chamber expansion, and cannot be "corrected" by neck sizing or other reloading methods. It is caused by battering and wear on the bolt locking lugs and lug seats in the receiver. If it is bad enough, here is what happens.

When the round is fired, the pressure "glues" the thin case walls to the chamber walls, while the solid rear of the case is free to back up. If it is allowed to back up too far, the case stretches beyond the elasticity of the case material and the case head tears off. Usually, this means only a headless case stuck in the chamber, not a big problem in civilian life.

But in a worst case condition, the case backs up to the point where its thin part is unsupported by the chamber, it bursts, and the high pressure gas destroys the action and possibly injures the shooter.

So excess headspace is no joke and there are no magic solutions in reloading or even rebarrelling. (Remember, it is the bolt lugs and seats that are worn, not the barrel!) Another, slightly longer lug bolt may work, at least for a while, but much of what you read about "solutions" to headspace problems is based more on wishful thinkiing than on knowledge.

Jim

 

[dmftoy1]

Thanks for that. I don't necessarily think any of my rifles have excessive headspace as I've never seen any indication in the brass, but I got to thinking when I picked up two new (24/47 and 91/30) rifles this weekend that I had never checked any of the rifles I have and that was probably stupid given that it's $17-$20 for the gauge.

I also have an Enfield that I bought last summer that I've never checked, a K98, and an M44 . . .so I can buy two gauges and check 4 rifles.

I tend to shoot lighter loads in these anyway (17 grains of 2400 under a cast bullet) but I figure it'd be good to know.

Have a good one,
Dave

 

[1911Tuner]

I don't necessarily think any of my rifles have excessive headspace as I've never seen any indication in the brass,

That's the catch. Sometimes you don't necessarily get indications until something lets go. Mil-spec brass is thicker and stronger than its civilian counterpart, and incipient case head separation often doesn't show itself
until the 3rd or 4th loading unless you know the warning signs. A bright ring
around the case at the web is the first indication. Don't ignore it.

It's strongly recommended that any military surplus rifle...or any used rifle with unknown history...be gauged for safe headspace. You never know what it's been through. Some people handload with no regard to listed data, and try to see just how fast they can drive a bullet before the case extraction starts to get sticky...and then they see if they get another 50 fps out of it. Then... if they're lucky...they notice the "ring around the case web" and recognize what it means...and trade the rifle or take it to a gun show to sell off to some guy who doesn't have a clue that he's about to fire a potential framentation grenade 10 inches from his face.

 

[Jim K]

Probably the "worst case" condition I ever encountered was a .308 sporting rifle that the owner had had rebarrelled by a "gunsmith" in his area. I don't know how it happened, but the "smith" apparently did not know how to ream a chamber and the cartridge wouldn't fit. His "solution" was to grind the back of the locking lugs. Fortunately the owner sensed something wrong and brought it to us without firing it. We figured that at least 1/4 inch of the case was sticking its little rear out into the air, a disaster waiting for a chance to happen. Yet, that rifle passed the NO-GO headspace check.

So there is a bit more to the whole headspace thing than just sticking in a gauge.

Jim

 

[1911Tuner]

His "solution" was to grind the back of the locking lugs. Yet, that rifle passed the NO-GO headspace check.

Seen that one, too. That "smith" wouldn't happen to be called "Big Bob" would he? I heard that he moved up north in the mid-70s.

 

[Clemson]

dmftoy1, I generally buy headspace gauges in sets, with GO and NO GO. But I fit barrels commercially, and those are the gauges that I need to do that work. For calibers that I only check, I buy a NO GO gauge. That tells me whether the gun is one that I want to buy. Yes, a FIELD gauge will will tell me whether it is safe to fire, but I really don't want to use a gun that will close on a NO GO for any extensive firing. It has stretched to the point where it exceeds the NO GO specs, and it will continue to set back until something bad happens. FIELD is OK for military circumstances -- Infantrymen are expendable. If I were you, I would use NO GO for my hunting rifles.

Clemson

 

[gunsmithgirl]

Yes, a FIELD gauge will will tell me whether it is safe to fire, but I really don't want to use a gun that will close on a NO GO for any extensive firing.

I agree I would use a no-go gauge.Far as I was taught field gauges were for military, if a rifle failed the no-go but passed a field it was still safe to fire. If a rifle fails no-go I correct from there, there is really no use for field gauges outside of a war zone in my opinion.

 

[Slamfire]

Probably the "worst case" condition I ever encountered was a .308 sporting rifle that the owner had had rebarrelled by a "gunsmith" in his area. I don't know how it happened, but the "smith" apparently did not know how to ream a chamber and the cartridge wouldn't fit. His "solution" was to grind the back of the locking lugs. Fortunately the owner sensed something wrong and brought it to us without firing it. We figured that at least 1/4 inch of the case was sticking its little rear out into the air, a disaster waiting for a chance to happen. Yet, that rifle passed the NO-GO headspace check.

So there is a bit more to the whole headspace thing than just sticking in a gauge.

Stuart Ottensen, in his first volume of “The Bolt Action", specifically in the Mauser 98 section, has excellent line drawings showing case head protrusion/support. Once I saw those, the whole concept of case head support became very clear, and the importance.

Unfortunately many folks just do not understand that case support is a critical safety issue. Equally unfortunate, I do not know how to measure that.

Any suggestions?

 

[berkbw]

I check case protrusion visually.

 

[dmftoy1]

Alright ..well I've already ordered 2 of the field gauges but for the 8mm I'm waiting and so I'll order a "no-go" for that one. I guess as funds allow I'll do the "no-go"'s for those as well.

Regards,
Dave

 

[dmftoy1]

Alright, the 7.62 x 54R and .303 British field gauges arrived today. (Forester brand) I took the Mosin's out of the safe, broke down the bolts and removed the extractor and checked to see if I could close the bolts. Definately couldn't close the bolt with the field gauge so I'm guessing I'm in good shape there. I might still buy a no-go gauge and retry just out of curiosity.

The .303 was a bit different. I took the bolt out, removed the extractor and then tried to close the bolt. With a bent bolt handle it wasn't obvious that it wasn't closing all the way but after playing a few times I could see that it definately wasn't closing on the gauge (handle all the way down). It was alot closer to closing than the Mosin's though. In doing a bit of reading on the Midway site it appears that the Forester "Field" gauge is "thinner" than the British Military Field gauge (.070 vs .074). I'm wondering if I should be buying the .303 "no go" . . .I suspect that it will close on it but I don't know. That raises the second question which is whether I should be trying to find a #3 bolt head. (#2 currently in). #3's don't appear to be too common.