I'm building my first AR, after buying many.

Whats the deal on Headspacing.
What is it, how do I utilize the guages, and how is it adjusted.

thanks for the patience and your time in answering my questions.

I did a search, but came up empty.

thanks

OK.  Head Space is the position the case is held in the chamber by the bolt or breach face.  Different firearms head space differently.  Most straight walled pistol cases head space on the case mouth.  Rimmed cases head space, or position the cartridge, with the rim.  Bottle neck cases position themselves on the shoulder.

Head space guages are shaped like the appropriate case but one is slightly over sized.  If your bolt closes on this guage you have too much (head) space in the chamber around a SAMMI Spec. case and the rifle is dangerous to fire.  If if won't close on the other one you have too little space and it is still dangerous to fire.

Adjusting head space is something best left to a GOOD gunsmith.  On an AR-15 too little space can be corrected by reaming the chamber a little deeper.  Too much head space is a little harder to correct.  You can turn a little bit of the breach end and then re-install the barrel extension, but you have to go 1 complete revolution of the extension in order to re-index the gas port.  Now you may have to re-ream because you may have too little head space.  This might not be worth the trouble because head space grows with use and if it's been shot that many times, to make the head space grow that much, the barrel is more than likely shot out anyway.

Ok, now let's talk about real headspacing when it comes to ARs -

Don't worry about.  If you really want to check it, buy the gauges, use them once, then put 'em away and wish you'd spent your money on something else.

You CANNOT adjust headspace on an AR, so don't even try.  Forget about reamers, because they won't work in a chrome-lined bore.  And if your AR doesn't have a chrome-lined barrel, it should.  Besides, headspace never shrinks, it always grows.

If you don't have gauges, you can use a cartridge.  If the bolt closes on it, you're ok.  Shoot it.  A little too much headspace will NOT make your gun blow up.

Personally I think it's a diservice to new builders to fill their heads with dire warnings of impropper headspace and ideas that you should use reamers or try and remove the barrel extension.  Nobody here does this, and it's far out of the capabilities of any except the most advanced machinist, and definitely out of the scope of any armorer.

Headspace is last thing you should be worrying about.  So don't.

"And if your AR doesn't have a chrome-lined barrel, it should"

Not if I have a SS barrel and I am looking for the best accuracy. Chrome lining the barrel is great to keep the cleaning factor down, but since I don't shoot in combat situations, chrome lining is not for me. Accuracy is my main concern.

But I do thank the both of you for providing me with the insight into the whole headspace/gauging thing..

By the way, when i see ads for new complete uppers, I know what headspacing is, but what is gauging?

Again, I have bought more than my share of AR's, just never have put my own together.

thanks again.

It's a myth that chrome barrels aren't as accurate.  And ARs need a chrome chamber to extract and function reliably.  Buy a so-called "match" barrel and you'll be spending a lot of time yanking on the charging handle in between shots.



Every day new builders post here asking why their new creations don't work.  That's why I always recomend building a standard rifle or carbine with a Colt or Bushmaster barrel as a first project, and save the fancy stuff for later after you've gotten some experience troubleshooting ARs.

Good luck with your project.

Forgive if I am being ignorant, but what does a chrome lined barrel have to do with shell extraction. The pressure inside a chrome lined versus a non chrome lined barrel will be a factor of barrel length and powder load not whether its lined or not.

Are you telling me that a chrome lined barrel will supply more pressure through the gas tube, thus cycling the bolt more reliably than a non chrome lined barrel? If so, please point me to that technical link.  As far as it being a myth, I will certainly entertain that thought, but my shooting experience, what I have read in technical manuals and shooter's opinions, etc all point to the fact that a chrome lined barrel is good for keeping wear down. Whereas match barrels, varmint rifles, and bull barrels are mostly non chrome lined stainless steel.

Personally, I own both kinds of barrels and don't shoot enough to have to worry about wearing them out or them getting fouled.

From what I have read, CL barrels prevent fouling problems and keep wear down to a minimum, but at the sacrifice of long range accuracy. Personally, I really don't know the technical aspects of it, but I listen to those old timers who know more than me, and its the predominant theory.

I welcome any and all experienced thought and discussion on this matter, but don't want to start a "which is better" thread.

Chuck

ok, I am definitely game.

what is the first thing I should worry about.
and the second.

sincerely I am asking.

Chuck

You need to get a copy of "The Black Rifle" and read it cover to cover.  Chrome-lining has nothing to do with pressure and everything to do with friction.  Chrome lining or (the lack of it) was THEEE BIG PROBLEM when the M16 was first issued in RVN.  Read the book.



Buying a good barrel and bolt.  Then the correct buffer and spring.  After that, nothing really matters all that much.  Maybe magazines.

I disagree with Homo's powerfully stated opinion.  How can it remain true in light of the fact that a person can buy a few extra bolts for their brand-new AR, test fit them with the gauges, and select the one that 'stacks tolerances' to the preferred headspace.  Doing so will allow the AR owner to tweak headspace toward either tighter or more generous than the spec. average.

This would be called adjusting the headspace, would it not?

I know this works because I've done it myself after having read about it here, from the more knowledgeable folks.  I think all new AR owners benefit from hearing every alternative more than they do from overly confident pronouncements.

I understand this, and I have read many technical publications on that very subject, but in vietnam, there were many issues not just non chrome lined barrels.

Now tell me again what does a chrome lined barrel do as far as shell extraction.

You stated that if I use a match barrel, that I should be prepared to use the charging handle alot more than I would with a chrome lined barrel.

why? The breech isn't chrome lined, and most people don't use CL bolt carriers, so why is it that you are telling me that a chrome lined barrel is important to the mechanics of a spent shell being properly ejected and a fresh round being slammed into battery.

Now I am going to disagree with this statement.

First of all, Eugene Stoner and friends designed the rifle to shoot 5.56 with stick powder, but the military supplied the troops with ball powder, coupled with the fact that they did not think the rifle needed to be cleaned. the popular mindset at the time was the rifle would clean itself. Well that was proven wrong when they started getting all gummed up and failing to properly extract a spent casing. This was THEEE problem.

A non chrome lined barrel proved to be prone to rust, wear and thus degrade accuracy, thus percipitating the need to replace the barrels. If you know anything about the weapon as it was used in Vietnam, is that for every 1 round that struck a bad guy, a thousand were fired over his head. The M16 was a full auto rifle in its Nam days. Soldiers would rock and roll with full 20 or 30 round mags when the fit hit the shan. My dad was a ground pounder in Nam and has told me all about how they did things over there. More rounds went wide and high than did go true to target.

Hey, I watch the History channel religiously :)
Just the other day, Tales of the Gun. The M-16 was on. :d

As far as I know, I won't be taking my non chromed lined barrels with me when I go trekking through the hot and humid conditions of a jungle for a tour of duty so I don't have to worry about rust.

Chrome lining in the chamber aids in extraction.  It's very hard and it's slippery compared to a SS or chrome-moly steel chamber.  Because of this it will also last longer.

Stainless and chrome-moly steel barrels will, over all, be more accurate.  The rifling in the barrel has sharper edges and is more consistent through out the length of the bore than an over sized bore plated to the correct demension.

It's always prudent to check your head space when changing bolts or assembling from new parts.  At the very least it won't hurt as much as metal in the face.

As far as stainless being more problematic, I suppose, over all, it's true, but I have 4 match semi auto rifles, a Garand with a chrome-moly, 2 AR-15s with stainless and an AR10 in stainless.  None of these rifles shoot factory loads.  In fact I ordered my AR10, Lilja 3 groove barrel with a very short throat and tight chamber.  It gives me more flexibility in finding the right bullet and load for that mythical 1 hole, 10 shot group.

All of these rifles function flawlessly, with NO pulling on the charging handel.  I just size the cases to 3/1000s under once fired and set bullet depth to suite their needs and accuracy tastes.

I have 2, 16" chromed lined AR-15s for burning up all my reloading misfits and any cheap surplus.

There's a couple of ways to guage head space.  The easiest is to use the "Go, No-Go" guages Like I explained in my first post.  There are other ways that check the demensions of the chamber.  Some are melted or composite mixtures that are poured into a plugged chamber, allowed to harden and then driven out and the demensions guaged.  I never used any other method than full length sizing the brass to the lowest my sizing die will go in the press.  After it's once fired it's pretty close to the actual demension of the chamber.  I use an RCBS precision Mic to set the die to nock it down about 3/1000s from once fired.

I thought the chamber was chrome lined on the better chrome lined barrels.

Not True?

Actually, you have it backwards.

Originally just the chamber area was hard chromed to aid extraction.  Later the whole bore was chromed for corrosion resistance.  Ease of cleaning is a nice feature, but ARs desperately need the slipperier chrome chamber to extract reliably.



This is why I keep telling you to read "The Black Rifle."  You are totally wrong - the chamber is chromed, and needs to be.  We can't help you unless you do your homework.  And regardless of what you saw on TV, the biggest problem with the first M16s was that McNamara didn't think chroming chambers was cost effective and nixed the idea.  Yes, the surplus Winchester ball powder that was substituted for the specified DuPont IMR stick powder was another McNamara cost-cut did create more calcium deposits.  But it was chroming the chambers that really made the M16 reliable.

So once again - do your homework, read the book, and don't believe everything you see on TV. [:D]

The reason I recommend against newbies building "match" ARs is yes, you could probably do it and it will probably work.  But with a tight chamber and no chrome, it's going to be finicky and tempermental - if it works at all, that is.  There's a reason that barrels are chromed and military chambers are cut loose - it aids with functioning under less than perfect conditions and with a wide variety of ammo.  Yes, you might give up a few M.O.A. when shooting from the bench, but it will definitely go "bang" everytime you pull the trigger, which is what you want in a combat rifle.  And these guns are made for combat.

My current personal favorite rifle is an pre-ban M4gery I built on a Olympic lower receiver with a 14.5" Colt M4 barrel and Colt bolt, with the rest of the parts picked up at gun shows made by who-knows.  This gun has never malfunctioned even once, gobbles up any ammo I shove into it, and at my last shooting session could reliable hit an 18-inch gong at 600 yards 7-10 times shooting surplus Canadian C77 ammo off-hand, standing, using iron sights.  That's my idea of a rifle.  And no, I didn't torque the barrel. [:P]

OTOH, if you don't mind having an AR that won't function every time, is sensitive to ammo, cleaning, and the environment, and you don't mind spending more time tinkering with it than shooting it, then by all means try and build a tack-driver as your first project.  Good luck.


[edited to ficks speling misteaks.]