Headspacing on an AR

Discussion in 'AR-15 Discussion' started by jhog, Jan 25, 2011.

  1. jhog

    jhog New Member

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    I have been looking at barrels and some companies give the option of getting a bolt headspaced to that barrel. So, if the bolt is housed in the carrier, how do you headspace the bolt to a "bare" barrel? This to me is confusing. I mean, how do you headspace an AR bolt?
     
  2. Squirrel_Slayer

    Squirrel_Slayer New Member

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    Been really curious about this myself.
     

  3. jhog

    jhog New Member

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    And another cool Avatar! Were do you get those?
     
  4. Dillinger

    Dillinger New Member

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    Go/No Go gauge, but you need the right one for the application at hand.

    .223 is different from 5.56 and both are different from Mil-Spec for the M16.

    Sounds confusing but really the difference is like 1.465" to 1.470" or 1.473" - something very near those numbers.

    What the manufacturers are doing is a CYA in case they are selling to a handloader and don't know it.

    "what? Barrel blew up on you with your reloads? You didn't have it headspaced by us? Sorry, this one is on you".
     
    Last edited: Jan 25, 2011
  5. JonM

    JonM Moderator

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    i dont worry about it mainly. just stick to the ammo the maker recomends. i reload for mine. all my chambers are 5.56 so i make my ammo to 5.56 spec. if you have a .223 chamber dont use mil-surp ammo only ammo marked for .223. if you put your own extensions on the barrel then you might need to buy some gauges for your application. i dont mess with putting on my own barrel extensions. i dont have the tools for it. used to in the army and the knowledge is faintly there in the back of my empty head rattling around somewhere. it prolly killed my ability to type some while back.
     
  6. jhog

    jhog New Member

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    OK so if I were to buy a berrel from, lets say, White Oak, it would be a good idea to also buy the bolt with it?
     
  7. mjkeat

    mjkeat New Member

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    Yes it would be a good idea. Im not 100% on why but have come to the conclusion through previous reading that it would give you the best outcome. When you purchase that BCG you'll have a spare bolt. Spare parts are always nice. THey eventually turn into complete rifles.
     
  8. Squirrel_Slayer

    Squirrel_Slayer New Member

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    The interwebz my friend.

    So if your chamber is marked 5.56, I should be A OK with my handloads if I only use the same kind of brass, Lake City, all the time? The LC stuff isn't marked with either .223 or 5.56, all it has on there is L C.
     
  9. jhog

    jhog New Member

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    I don't think that would matter so much cause once fired brass from your chaimber is formed to your chaimber however, I'm not to sure about fire forming .1223 in a 5.56 chaimber. Maybe someone else could enlighten us on that? Someone that reloads alot.
     
  10. JonM

    JonM Moderator

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    its not the brass its the dies and where you set the head spacing. case gauges are important for getting the proper headspacing for your dies. 223 brass will fire just fine in a 5.56. 5.56 will fire in a 223 but you may run into chambering issue and feed reliability which is why the manufactuerer doesnt recomend it. also repeatedly loading to 223 spec and firing out of 5.56 chambers will wear your brass out much faster due to the constant stretching and resizing.

    thats why you should set your dies accordingly for each chamber and why i dont mess with .223 chambers just to preserve the life of my brass. it doesnt matter really which you have its just easier to stick with one or the other for extended brass life and ease of setup for reloading if you have multiple ar15's that shoot 223/556
     
  11. jeepcreep927

    jeepcreep927 New Member

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    5.56MM brass can absolutely be resized and reloaded to .223 pressures/ specs. The exterior dimensions of the cases are no different. The difference is in the length of the leade (chamber throat). The .223 chamber is usually cut to .085", where as the 5.56 is usually about .162". The shorter leade in a .223 chamber causes higher chamber pressures if 5.56 rounds are fired in it and *may* damage the rifle.

    Some 5.56 brass *may* be thicker near the base, but not always. .223 in a 5.56 chamber may adversely effect accuracy due to the free bore.

    If a rifle has a really high round count (like tens of thousands of rounds) swapping the bolt into and out of different uppers isn't advisable. For a new bolt and new barrel, the chances of having a head space problem are slim. As JD mentioned, if it bothers you, you can purchase go and no go gauges for your chamber (.223 OR 5.56). They will only tell you that you're head space is within certain parameters. To adjust head space the barrel extension needs to come off and the chamber re-cut or the barrel set back or both, depending.
     
  12. Dillinger

    Dillinger New Member

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    Okay, quick time machine travel back to my first attempted post from last night.

    The information thus far has been correct and thanks for the extra explanation Jeeper. ;)

    The AR receiver has a shoulder pre cut and all AR barrels (well, 98% of them ) come precut with a lip that fits on that shoulder and your headspace should be A-ok.

    Many people will tell you that you can slap an AR together and never worry about headspace. And they are right too, but to a smaller extent.

    With the loose tolerances of the chamber ( 5.56mm ) and the fact that people shoot different ammo out of the weapon ( .223 Civilian ) unless you are building a long range, serious target gun or varmint rifle, this minimal space is not going to affect you.

    Operator/Mall Ninja A; Builds a 14.5" barreled ( 2" flash hider to make it legal ), clam shell front end, A2 sights, A2 carry handle and his own lower. Head space is not going to be in issue with 95% plus percent of the ammo he is ever going to fire.

    Operator/Mall Ninja B: Builds an 18 inch factory, chrome lined barrel, free float tube, muzzle break, flat top, puts a collapsible stock and $650 worth of glass on it. Still not really going to have problems with headspacing. He will be fine with off the shelf.

    Tango: Builds a 22", White Oak armament bull barrel, YHM free float tube, BUIS, on a matching billet Upper/Lower with a Leupold fine duplex 4.5 x 14 on Badger Ord rings and has the chamber of the barrel cut to a specific cartridge length/spec in the .223 caliber that he reloads too and wants to use for his varmint gun. Tango makes sure to get his weapon headspaced properly as he is building a long range target model and not a SHTF rifle.

    See the difference??
     
  13. Squirrel_Slayer

    Squirrel_Slayer New Member

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    So on the .223 what is the part of the cartridge that stops forward movement in the chamber? The length of the case neck?
     
  14. Dillinger

    Dillinger New Member

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    I am not sure I understand the question.

    Do you understand the difference between a rimmed and rimless cartridge and how each sits in a chamber?
     
  15. Squirrel_Slayer

    Squirrel_Slayer New Member

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    I do understand the difference between a rimmed and rimless cartridge, yes, but how rimless cases sit in the chamber is something I have never really contemplated till this point. Duh for me. I am just trying to understand the importance of case neck uniformity in relation to head spacing and pressure issues, not just case neck tension.
     
  16. jhog

    jhog New Member

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    So if I understand right, if I have a White Oak .223 varmit upper assy., in order to get good groups @ long or short rsnge I need to shoot .223 ammo? And the same if it were a 5.56 + 5.56 ammo? Is this correct?
     
  17. Dillinger

    Dillinger New Member

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    Okay so you understand on a rimless case that shoulder is what is set against the tapered chamber of the barrel and that the bullet itself is free floating in the chamber and not jammed right into the lands and grooves. Correct?

    When you hear of shot cases being "fire formed" what is happening is that the pressure, and heat, on the brass is expanding rapidly to push the walls of the cartridge case against the chamber that was cut by the barrel reamer.

    Generally it (your chamber) will be just a couple of thou off/over the spec of the round so that you can get the catridge in and out.

    Too much pressure causes the brass to misshape in the chamber and is one of the things that cause a case to get stuck after firing.

    In an ideal chamber, the brass is a perfect fit around everything but a small portion of the area right around the bullet, before that bullet enters the lands and grooves to generate rifling and transfers that explosion of primer and gunpowder into torque.

    Improperly applied, the explosion of primer and gunpowder creates gas that has time to push the bullet forward, but also build up back pressure as the round that is traveling straight is forced to start rotating. Too much pressure and you get a blowback situation.

    This is one of the key reasons you hear of locking lugs and lug lock when talking about quality rifle actions. If those locking lugs are not tight against the action, or weak in any stretch, that pressure has to go somewhere. :eek:
     
  18. Dillinger

    Dillinger New Member

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    At the very basic level, yes, you are 100% correct.

    You have to define "good" groups and you also have to factor in harmonics and outside influences on the barrel in question. Not to mention the lock up between the bolt face and the chamber, but yes, you are correct.
     
  19. mjkeat

    mjkeat New Member

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    Couldnt he go w/ the Wyld (spelling) chamber for better accuracy over the board?
     
  20. Dillinger

    Dillinger New Member

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    Yes. I was waiting who would ask that question first. :p Cupie doll for you.

    Here's the problem with the Wylde. It allows you to shoot both 5.56mm and .223 with reasonable accuracy. However it shoots NEITHER of them with great accuracy until you fire form some brass and reload for that specific chamber specs.

    Now the same can almost be said to be true for any 5.56mm rated chamber, except that it will give better accuracy for it's 5.56 round and slightly less accuracy for the .223 when compared to the Wylde.

    Since 5.56mm is FAR more common across the mainland of our current occupied terror-tory, it is the smarter choice in MY humble opinion.

    YMMV

    JD