I just built two ARs, a pistol and a 14.5". I have yet to fire them, but I did not check headspace (or even know what it is).

Is this mandatory, just a good idea, or unnecessary? I just saw mention of it in some GD thread and it got me thinking.

Educate me, please.

No one else chiming in so I'll tell you my version. I'm a long-time shooter, fairly new to AR's. Been shooting my first AR for a few months now. It's a build gun. Headspace checking, to me, was mandatory:
1. Best case: Not checked, saved money. Good quality parts go together like they were meant for each other. Bang bang, shoot shoot. Much fun is had.
2. Worst case: Not checked. Bunk parts or even Monday built parts from a top-shelf manufacturer. Tolerances stack up hyper FUBAR. Boom in your face. Worst day ever. Money saved, but you or someone else is dead.
3. Normal case: Check it even if you're 99% sure. It's a gun. Why take a chance on some strangers' quality/safety mindset and skills? BONUS: Now you have a baseline measurement against which you can gauge wear and tear.
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ETA: Order gauges and learn all about headspacing while you wait for them to arrive OR have it checked at a local smith that is AR-savvy OR borrow a set from an AR friend and, even better, have 'em walk you through it
Do you know how to strip your bolt?

Thanks for your reply.

Yes, I can strip the bolt. These are my 3rd and 4th AR's. I bought my first as a complete, the second in two halves, and you know how the disease goes. I bought parts for the two, ended up with a bunch of take off parts, said, "Hey, Ill just make these spare parts a gun of their own". Then it was all "salad days" and, "I should just make a pistol while Im at it". So the two Im talking about were put together piece by piece.

Im very safety conscious, and would spend the time, money, or energy that is necessary to stay on the safer side. So its certain at this point I will be doing headspace checks (or whatever you'd call it). Im going to do some searching and Ill do my best to educate myself. I'll probably take them down to my local AR smith to have him double check all my work, as these are my first and I'd like to be "sure". My only real concern at this point is the headspace.

And Ill always take any opportunity to buy more tools. Gauges here I come.

Thanks again.

With good quality parts it is unlikely you will have a headspace issue.

BUT

It only cost $50.00 worth of gauges when you could possibly blow up your gun and cost you hundreds and possibly injury yourself or others.

Be safe and check it.

As you continue to build you have to make decisions at key points.  
Are you never going to check headspace?
Are you sometimes going to check headspace?  How do you tell when to check and when not to?

I just check it each and every time and then it's done.  Sorta like making sure the torque settings are right.  
Maybe get away without it , but doing it becomes just part of the normal work flow and is a safety guard.

Way back in the day, when there were only a few sources of bolts and barrels, you could count on all barrels and all bolts being within spec and safe to use together.  Those times are long past, and it's impossible to know exactly who made most of the bolts out there, and often who made the barrels too.  Especially if you used something other than dead-stock bolts and standard barrels from highly regarded manufacturers, it's a VERY good idea to check headspace on a build.

Headspace is the distance between the bolt face and a specific point on the case's shoulder (which is defined specifically for each caliber), and is measured with case-shaped headspace gauges.  There are two important gauges: the GO gauge, which checks for at least a minimum chamber; and the NO GO (or FIELD) gauge, which checks for a maximum chamber.  The bolt should close on a GO gauge, but should not close on a NO GO or Field gauge.  Some people will say that closing on a a NO GO gauge is not a failure, but that's only true on a barrel that's been fired a lot.  For a NEW barrel, if the bolt closes on a NO GO gauge, the chamber is already at the "really worn" depth, and the barrel is not acceptable

Never mind - GH covered it .

To resolve potential ambiguity, I must note, for OP's benefit, that the "NO GO" and "FIELD" are definitely two separate gauges that mean two different things.

Otherwise, my understanding is right down the line with "GHPorter".; ie.:
- Closing on the NOGO gauge means "very little service life remaining on this bolt / barrel combination" - Probably GTG for a short gunfight in a pinch.
- Closing on the FIELD gauge means "the service life on this bolt / barrel combination is all used up" - If a gunfight comes to you, you might stand a better chance of survival by waiting for it to get REAL close and beat it to death with the buttstock, or hand the rifle to Private Fragbait and let him shoot it.

For the military, closing on a NOGO gauge being "not a failure" is a judgment call; resources, budgets, battlefield conditions, on and on.
For civilian / recreational shooting, closing on a NOGO means it's time to replace barrel and/or bolt. There's no up-side risk like there is on a battlefield.
If it's a bolt / barrel pair shipped to you as "new", time for a refund.

My $0.02 x 4

Why the AR doesn't need to be checked in the same way a traditional firearm does, is because of it's construction. The traditional barrel has the bolt lugs in the receiver. The barrel is press fit and pinned to it, and in the process the headspace is set.

With the M16/AR15, the barrel extension with bolt lug recesses is screwed onto the barrel, headspace checked, then it's pinned in place. Then the gas port is drilled relative to which way is "up" vs the ramps. The pin in the barrel extension is basically a friction fit against the threads and they could still be turned relative to each other if enough force is applied. At that point the gas port could be plugged and redrilled, or an annular ring macihined on the inside of the gas block to access the port.

Most barrels already come headspaced, and the custom makers will headspace onto a bolt they can include.

IIRC the factory for the M16 don't headspace a specific bolt - in fact the armorer has to select and check it if replacing it in the field. That is why there are headspace gauges and instructions on their use. And that is exactly what the industry has been doing, selling barrels headspaced with no bolt to be supplied by others.

It's the gunsmiths who caution it need to be done, and on traditional rifles it's mandatory. Stoner designed the M16 to sidestep that labor intensive task and reduce the time it takes to assemble them, along with about 100 other things.

Everybody cusses and discusses direct impingement, when the barrel extension is as much, if not more important, an advancement.

Works pretty darned good for deploying 1,000,000 guys with 1,000,000 rifles in a big-ass hurry too, I'll betcha'! Modularity, serviceability, multi-sourcing of the supply chain, etc... So long as ass-kicking military grade specs and tolerances are clearly spelled out and enforced rigorously at the factory(s). Being just one guy building one rifle for Saturday fun, I don't wanna be "that guy" who gets the one blooper.

As long as the bolt measures 0.156" from the back edge of the bolt's lugs to the bolt-face, and the barrel measures 1.6206" from the inside edge of the barrel extension's lugs to the 0.330" datum line; the headspace will measure the minimum headspace for a new barrel that's been high pressure tested (HPT) which is a headspace that measures 1.4646".

First of all, You want to check your barrel before you put it together with the bolt your going to use. 95% of all factory barrels headspace just fine.  About 2% of the barrels I have installed have been short chambered. Only 2 barrels I have ever had were so jacked up that they were dangerous to fire.  I have put together around 1500 uppers in the last 20 years. Last but not least is if your barrel doesn't headspace properly the only recourse is to send it back to the manufacturer, you really can't change it once the barrel extension has been installed and the gas port drilled.

It is important that these gauges be of the same manufacturer.  You do not want to mix gauge manufacturers when purchasing.  Mixing tolerances between manufacturers could create issues.  Buy them as a set from same manufacturer.  I have Manson gauges.  They are machined to accept the ejector pin so your bolt does not have to be completely stripped.  

 

Using headspace gauges is almost trivial, and they allow the user to assess all of the above in a quick and easy process.  GO and NO GO gauges give the user the two pieces of data needed to assess the safety of a new barrel and new bolt: that the chamber is at least at minimum depth to the datum point (that's the GO gauge), and that it is not more than a maximum depth to the datum point (the NO GO gauge).

A FIELD gauge is typically a little longer/deeper than a NO GO gauge, and it's purpose is to identify when a chamber is even deeper than what the NO GO gauge measures.  In military usage, the NO GO gauge is used to identify rifles that should not be deployed in operational use, while the FIELD gauge identifies rifles that must be removed from operational use.  In the context of this discussion - new bolt and new barrel - a bolt closing on a NO GO gauge should fail a NEW barrel/bolt combination, since it measures the maximum acceptable chamber depth.  A NEW barrel and bolt should not be anywhere near that depth.

I agree that one should stay with the same manufacturer for both the GO and NO GO gauges, which helps avoid confusion about which value you're using for what is OK and not OK.

I have been working on a build  for a while......I  have a question.....what brand  of gauges should we get.....is one brand better  than another, I was looking  at some at brownells I noticed some of the specs are  different.
thanks everyone.

I have Forster and they work fine, but I do need to remove the extractor and ejector from the bolt to avoid pressure on the gauge.

Lug uses the Manson, and it looks like there are cut outs making it unnecessary to remove the extractor, at least from the photos on Brownells.  I don't see a cut out for the ejector.

Lug, comments?

The advice in the sticky of this section is really good.  Basically, make sure you have the CORRECT gauges. The labels GO, NOGO, or FIELD are not as important as the actual size of the gauge.  Take a look at this link:

http://www.ar15.com/forums/t_3_4/315921_Headspace__Torque_values__and_Barrel_Break_in.html

My Manson gauges have a nice machined slice that allows the EJECTOR room to sit so it is not necessary to remove it.  My opinion is Manson is good quality stuff.  I purchased direct from Manson.
 

One key thing, they will not tell you what your barrel's actual headspace is being headspace gauges are only pass/fail measurements.

On another note, with the amount of headspace threads on ARFCOM, it's evident not many understand how headspace works, its purposes, and what points are measured to set headspace. Also, when a chamber fails a gauge, not many know what to measure to find out if the problem is the barrel or the bolt. The prints above removes that mystery.

One last thing, headspace is not just a safety check, for it will determine a new barrel's endurance after 50 cycles or 6,000 rounds. Since, new barrels that have been proofed, after 50 cycles, are not allowed to grow in headspace from the initial headspace measurement more than 0.0028" or surpass 1.4730".

SAAMI sets civilian cartridge and headspace specs, the military sets its own specs.
The SAAMI website has caliber specific drawings for cartridges and chambers.
The primary reason for the specs is to insure a maximum spec cartridge is safe in a minimum spec chamber and vise versa.
Ammo is not typically manufactured at the max tolerance so a person who has a weapon that would fail a Go gage would not necessarily know he had a problem until he used ammo at the max tolerance.

You're correct, but most people don't need to know what the actual headspace is, only that it's within specs.  Your point about the prints is great, though.  I'd say that anyone who has access to even a modestly useful depth gauge could easily determine what part was out of spec by just using that information.  With a new bolt/barrel combination, my money would be on the barrel every time, but it's obviously not that simple...

My neighbor and I just finished two builds. We did not check headspace. Shot the heck out of the rifles over the weekend.

If you have a local smith see if they can check for you, or you can always spray and pray.

I'd bet 90% of the builds you read about on this forum never checked headspace, so ,odds are in your favor.

If it was mandatory people would be lining up to scream at you to do it before you're even done hitting the  "submit" button.

I have had several barrel/bolt combinations fail Go gages.
In my cases it was always stacking tolerance so it was easy to fix.
There are no odds for the person that checks headspace.
For people who do not check headspace I think the odds are excellent they will not have a noticeable problem.
I also think it is interesting to note that when ammo like that recent lot of bad Winchester gets out it does not cause KB’s in every weapon it is used in.

I bought a rifle from a (huge) shotgun manufacturer and it shot poorly. I decided to check the headspace on my new rifle. Almost closed on a (.308) field gauge. They in formed me that their in-house spec. was .002 over no-go.
Moral: check the headspace on every gun you buy or build. If it is worth doing, it's worth doing right.