Checking Headspace on AR-15 Rifles

[pert near]

Like a lot of shooters, I'm enjoying the bargains that keep popping up on AR-15 parts. A good deal on barrels from one place & a good deal on bolts or BCG's from another place. Mix & match parts & save a ton of money!...LOL

But only on the more expensive barrels are bolts pre-check for headspace to your barrel if bought at the same time. I've check on a set of gages & a go, no-go, field would run about $100. There goes any savings. Where I live, going to a gunsmith for a headspace check is not easy or free. Is there another way to check for normal headspace using a sized case & a shim or some other method? Perhaps expand the neck & size to a crush fit, single fire, then measure case dimensions? Not sure if that would work & what dimensions to look for(?)

Just want to check for safety & assure all is within acceptable tolerances.

TIA for your comments & suggestions.

 

[243winxb]

. Is there another way to check for normal headspace using a sized case & a shim or some other method?

No

https://www.thehighroad.org/index.php?threads/ar15-new-build-and-possible-headspace-issue.824277/

 

[BBBBill]

Nope! You might rent or borrow the gauges from someone.

 

[entropy]

You can get by with go and no-go, you don't need field.

 

[boom boom]

No, there is no substitute for that--some might advocate using live ammo or maximum sized dummy ammo to replace a go-gage but remember that you could end up with a high pressure situation as brass will compress at the shoulder when doing so versus a gage.

Catch Brownells on sale. Right now a Clymer gage is $29.00 for a no-go in .223 and 33.00 for the same in 5.56 Nato. They sell a Colt MFG no-go for $25. Midway also has them. Fleabay also has them for sale often by someone who has finished a project. If you wish, you can rent them via Reamers4rent or a few other places. If your project is a one-off, you probably can get some of your money back by selling the gages on ebay after use.

One difficulty of checking the AR is that you will need to remove the ejector and extractor from the bolt for an accurate reading so you may need a bolt disassembly tool for that.

 

[pert near]

You can get by with go and no-go, you don't need field.

Hmmm....Why do you need the "go" gauge? If a factory or FL sized case goes in & locks, that seems like a "go". Just wondering.

I asked the original question because I can imagine very few AR one-time "builders" who put their guns together in their garage, avail themselves to headspace gauges. Instead they probably just shoot the first round off from the hip & see what the case looks like. (I recommend the "away-from-the-face-first-shot" on any new rifle, regardless of who built it.) Its one thing for a rifle to shoot & function properly as long factory ammo is always used. But if you want to be assured that all is within SAAMI spec's I guess the gauges are a must. A handloader can easily adjust for a slight headspace problem, but if you want to load generic, safe ammo for any rifles in that caliber you need to be standard.

 

[boom boom]

If a firearm fails the go gage, the headspace of the rifle is too short. This too short headspace can lead to pressure spikes or even out of battery detonation if worst comes to worst (stuck firing pin, extractor hitting the cartridge when it jams going into or out of the chamber), etc.

Factory ammo (and depending on the handloader's quality assurance program) often vary in cartridge overall length and bullet profiles even from the same manufacturer unless you are shooting one brand of match ammunition. All ammo is supposed to conform with SAAMI or CIP (Euro) specifications but remember that these are a range. That is why you use a go gage--given that semi-autos encourage firing a lot more rounds than perhaps a bolt gun, an out of spec firearm (too short) could be an accident waiting to happen.

In addition, headspace gages are not made out of aluminum or brass like cartridge cases because they can compress when the bolt is closed (which would also ruin the gage)--even steel headspace gages can be ruined by improper use in some bolt guns (the 1917 rifle is infamous for this as that bolt design gives tremendous leverage for closing on bad ammo).

The problem with using brass as a trouble indicator is that you can be well past safe limits when it occurs depending on the firearm.

The price of a go gage is about three 20 round boxes of ammo. The price for medical care is significantly more.

 

[243winxb]

A head clearance of .014" may cause case separations. Are you feeling lucky.

 

[entropy]

Hmmm....Why do you need the "go" gauge? If a factory or FL sized case goes in & locks, that seems like a "go". Just wondering.

I asked the original question because I can imagine very few AR one-time "builders" who put their guns together in their garage, avail themselves to headspace gauges. Instead they probably just shoot the first round off from the hip & see what the case looks like. (I recommend the "away-from-the-face-first-shot" on any new rifle, regardless of who built it.) Its one thing for a rifle to shoot & function properly as long factory ammo is always used. But if you want to be assured that all is within SAAMI spec's I guess the gauges are a must. A handloader can easily adjust for a slight headspace problem, but if you want to load generic, safe ammo for any rifles in that caliber you need to be standard.

You use the go gauge to set the headspace. You use the no go to be sure out of spec ammo will not chamber and fire. "pert near" ain't good enough. This is what separates professionals from guys named "Lefty."

 

[BBBBill]

Why do you need the "go" gauge? If a factory or FL sized case goes in & locks, that seems like a "go". Just wondering.

Then you are assuming that the round is actually in spec. Sometimes they are not. At any rate, the loaded round is NOT going to be the same dimensions as a gauge. Look up the dimensioned drawings for a loaded round and the finished chamber. There are significant dimensional differences.

 

[entropy]

Then you are assuming that the round is actually in spec. Sometimes they are not. At any rate, the loaded round is NOT going to be the same dimensions as a gauge. Look up the dimensioned drawings for a loaded round and the finished chamber. There are significant dimensional differences.

Not to mention the aforementioned tendency of brass cased rounds to crush. Hardened steel gauges don't.

 

[boom boom]

Not to mention the aforementioned tendency of brass cased rounds to crush. Hardened steel gauges don't.

There is an amusing anecdote in Hatcher's Notebook where the DCM (now CMP) received complaints post-WWII about the headspace on 1917 riles that were specifically re-arsenaled to specific safe headspace ranges. In the investigation whether it was by Hatcher himself or someone else (I can't recall), it was determined that the gunsmith was failing the rifles as too long headspace by tossing the no go gage into the chamber and trying his hardest to slam the bolt home. Given the leverage that the 1917 rifle gives on closing, the gunsmith was crushing the gages--checked using proper techniques--the rifles all had perfect headspace.

 

[BBBBill]

Gauges and chambers can be damaged if the gauges are used incorrectly.

 

[USMC22]

Where are you located? I have gauges, may be able to help you out. If I'm not close try ar15 forums, someone else may be close and willing to help out.

 

[Bang!]

What would you do with an AR that fails this check? What is the fix action? What could cause this condition to happen? What did the person assembling the AR do wrong? Is it totally up to the specs of the manufacturer?

 

[pert near]

I've never had the problem, but my understanding is that the problem is usually the bolt. So the first step would be to try a different bolt(s).

 

[grampajack]

What would you do with an AR that fails this check? What is the fix action? What could cause this condition to happen? What did the person assembling the AR do wrong? Is it totally up to the specs of the manufacturer?

In most cases the solution is to send the parts back to the manufacturer. If you have a mic you can check the bolt to rule it out, so you know which part it is specifically that's causing the problem. Since it's such a big safety issue, I would be surprised, shocked actually, if the manufacturer gave you any grief over it, especially if the bolt and barrel came from the same place, which I tend to find preferable in the first place.

If it's a custom barrel and holding the responsible party accountable is not an option, it can be fixed at some to excessive cost. If it's too short, you can ream it with a pull through reamer (assuming it's stainless or cmv), and that's a very easy fix. If it's too long, then you have to remove it from the barrel extension and remove material off the shoulder. The tricky bit is timing it correctly for the gas port to line up again, so you would likely have to short chamber it, then ream to fit after it's back in its extension and the gas port is lined up. I can't think of any scenario where this wouldn't just be more trouble than it's worth, unless you have your own lathe. If it's chrome lined or nitrided, then it's scrap metal.

 

[Varminterror]

Parts manufacturers and barrel makers are no less accountable for their products than any firearms maker. Grab a depth on the bolt and confirm 0.125", if it's not, the bolt is out of spec. If it's in spec, then the barrel is chambered improperly, and they'll owe you a replacement.

It's really that simple. Drop a spindle tomorrow and you'll know who you need to call.

 

[BBBBill]

Another bolt dimensional error that can also contribute to the problem is the lug length front to back.

 

[boom boom]

One problem with new bolts and barrels is that the headspace may be too short as well as too long as others have listed above. Thus, you need the go and no go gages for assembling new rifles of any sort (bolt actions etc.) (field gages are generally for used weapons to determine whether it is unsafe to fire). Tolerance stacking by assembling parts from different manufacturers even in the day of CNC milling can get you. One way around buying headspace gages is that if you trust the manufacturer/seller is to buy a bolt/barrel combo, you can have them check the headspace for you. The other is to get the bolt from whoever you want and the barrel from whatever seller floats your boat--then you need the headspace gage set and be prepared to return whatever component (barrel or bolt) that causes the rifle to have too long or too short headspace. BTW, I also recommend getting a bolt ejector remover tool as this should be removed along with the extractor to check headspace--also useful for cleaning the ejector hole and maintenance to it.

The .223/5.56 gages are simply too cheap not to get them as insurance if you build out of whatever source. Yes, you will probably be alright without them given the state of modern manufacturing depending on your tolerance of risk but suppose the ratio (which is unknown) is something like 1/30 or even 1/100 chance that something is wrong and you fire that rifle. It may even fire ok for a while until you change the ammo or don't clean it properly then TROUBLE. Some people's attitudes remind me of the Challenger disaster in 1986--they had never tested the O-rings on the space shuttle boosters at that launch temperature before (around freezing from what I remember)--the higher ups at the firm involved said to NASA that it would most likely be perfectly safe. Not so.

I do not like hassles so I generally follow the barrel/bolt combo from the same seller (typically a manufacturer/seller) and I generally source the build such as uppers and lowers from the same source/manufacturer to ease returns. I probably pay a bit more and risk not putting fashionable parts on the rifle. But, I am an untrusting sort so I check with gages also because an improperly assembled rifle is simply a long pipe bomb--that can blow up with nasty sharp metal bits and parts. I also use a torque wrench to check barrel torque even though the AR std. is remarkably generous on the torque range for a rifle barrel compared with a Mauser.

Have you checked medical care prices recently? The proper tools are cheap compared to that and you still have the tools afterward for resale or use in future builds--no so for perhaps your face, teeth, fingers, etc. after emergency medical care.

 

[AlexanderA]

One difficulty of checking the AR is that you will need to remove the ejector and extractor from the bolt for an accurate reading so you may need a bolt disassembly tool for that.

The military-issue headspace gauges for 5.56 mm are machined to clear the extractor and ejector, so there is no need to remove these parts. Commercial gauges may not have this feature.

 

[243winxb]

The military-issue headspace gauges for 5.56 mm are machined to clear the extractor and ejector,

Would this be it?

 

[boom boom]

The military-issue headspace gauges for 5.56 mm are machined to clear the extractor and ejector, so there is no need to remove these parts. Commercial gauges may not have this feature.

You priced a military gage in the wild lately. Commercial gages are cheaper even with hassle of buying a bolt tool.

 

[BBBBill]

Additionally, .223 Remington and 5.56 NATO are not the same spec. Chamber dimensions are different and care should be taken to keep 5.56 NATO out of a .223 Remington chambered gun. If the .223 chamber is on the generous side and has a long throat you won't see a problem, although the accuracy will most likely not be as good with either round. If it is a minimum spec .223 chamber pressure will spike. Some folks dismiss that, but I've seen the results of making that error. Expensive lesson....

 

[AlexanderA]

Would this be it?

Yes, the 1.4730 Field Service gauge (drawing number 7799734) is the one you see most often. Normally, that's the only one that's needed to determine if a rifle has developed excess headspace. If the bolt closes on that (without being forced), you need to replace the bolt and/or the barrel.