Headspace for off the shelf ammo - 6.5 creedmoor

Discussion in 'Gunsmithing' started by Mram10us, Oct 26, 2019.


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  1. Mram10us

    Mram10us Well-Known Member LRH Team Member

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    I DO own go and no go gauges too. But why not take an extra step like I explain in post #44? I could have been like a couple of you and said, “you guys are lazy for NOT taking the extra step and headspacing that guys 308 for the fed gold medal match he’s going to be using”. I don’t do this for a living BUT that doesn’t mean I don’t know how to make a safe and great shooting rifle. I understand saami and know it gives a MUCH bigger window than go nogo gauges do. I DONT appreciate when I get attacked rather than asked to clarify.
     
  2. J E Custom

    J E Custom Well-Known Member

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    Maybe we need to start over. The reason most said this method was not a good idea as a final head space was not to criticize anyone, It is just to help those that read how to do things that could cause them problems in the future.

    If an experienced smith were to use the cartridge case as a head space gauge he would probably know exactly where it fell within the SAMMI tolerance and with his experience and feel, He could do a good job of getting the chamber close. "BUT" if someone reads this that has never done it and doesn't understand what he could end up with, that is what most members are trying to prevent by not recommending this method, not to criticize anyone that is using it.

    Before SAMMI, Weapons were individuals and the chambers and bore were one of a kind and even the bullets were made for that weapon only. When mass production came along Standards had to be set so they could be mass produced and ammo could be used in all weapons of that cartridge. There also had to be standards for minimum and maximum dimensions of manufactured ammo so it could be chambered in that weapon because it could be made by many different ammo producers.

    Now, most everything precision is made to a standard and in the case of cartridges, the go and no go gauges are "THE" standard and if used any or all ammo should fit within the excepted tolerances. If you cut a SAMMI chamber, and the ammo for it doesn't fit, The Ammo is not within SAMMI specifications. If you use ammo that is not within SAMMI specs to set head space, your chamber will not be Within SAMMI specs, So why not use the SAMMI spec. gauge in the first place and know exactly what you have and that any ammo should work.

    When Chambering I use a loaded factory cartridge to check how the chamber is progressing because it checks the fit of the loaded round, but when I get within .100 thousandths of the final chamber, I switch to a go gauge and use it to set the final head space. Cartridge cases have a certain amount of compression ability and can give a false reading of several thousandths so they are not recommended for used for final head space

    Note: Different cartridges and uses require different head space for the best results, And a Hardened SAMMI gauge is the only way to set the different head spaces precisely that are required. Some cartridges are set at zero (.0000) head space, some are set at .0005, Others are set at .0015 and as a general rule most are set between .0015 and .0025 so a head space gauge that has no flex or compression is required.
    Once they are fire formed they all should have zero (,0000) head space and the sizing of the case dictates the chamber fit from then on.

    So while not speaking for others, I think what they, like myself were trying to say was that it is not the best way to head space a chamber.

    J E CUSTOM
     
    bigngreen and MNbogboy like this.
  3. shortgrass

    shortgrass Well-Known Member

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    I will put this as simply as I can. After the chamber is established, it won't change unless the rifle is abused. It, the chamber, is the 'constant'. Ammunition is the variable, whether it is factory made or hand loaded. One 'batch' to the next won't be 'identical' in size. Hand loads prepared by a prudent and careful person are probably closer to being 'identical' than factory produced ammo when it comes to physical size of the cartridge case as the 'hand loader' has control over size to fit his chamber. Factory ammo can and does vary over the industry tolerance. You have no control over that, the manufacture does, and if it falls within spec he will produce it. There is a very small .002" to .004" overlap of bottle necked cases in minimum chamber and maximum cartridge headspace lengths. If your chamber/ammo falls into this category, feel lucky as it won't be the case every time. Ammo can be made to fit a chamber. Chambers aren't fit to the ammo, as the size of the ammo is the 'variable'.
     
  4. Mram10us

    Mram10us Well-Known Member LRH Team Member

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    Just shot 8 types of bullets thru it today at 200. 5 shot groups. Seemed to like most of the handloads. 80 rounds now down the tube. A good cleaning and I’ll try some ladders with the 130otm and 140vlds
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