300 Win Mag Headspace

Discussion in 'Reloading' started by Daerider, Sep 28, 2018.

  1. Daerider

    Daerider Member

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    Hi, I am going to make a headspace gauge for 300 Win Mag, but I do not want to make it to SAAMI specs (.220"). Does anyone have some ADG 300 Win Mag brass on hand that they can take an average measurement on 5-10 pieces of brass from the base to the front of the belt? Would be very much appreciated.

    Regards,
    Dae
     
  2. can1010

    can1010 Well-Known Member

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    not sure what your trying to accomplish because once you fire and resize to bump shoulder it makes the belt useless for headspacing. but to your request ADG Brass .218-.2195 with one short .216 out of the twenty I checked. I would just use the SAAMI spec and save trouble down road
     
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  3. woods

    woods Well-Known Member

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    Every rifle has an individual headspace and every lot of brass can (and usually does) have a slightly different headspace. Knowing someone else's dimensions will not be definitive for you.

    On 300 Win Mag best to fire 3 or 4 times until your fired/unsized brass gets a slight crush fit in your chamber and then push the shoulder back .001" or so.

    That would mean you are now "headspacing in the shoulder" which would mean less chance for a case separation and best fit for your rifle
     
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  4. Daerider

    Daerider Member

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  5. Daerider

    Daerider Member

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    When I cut new chambers for belted magnums, I normally set headspace on the belt based on the average measurement of the lot of brass that i intend to use for the life of the barrel to minimize stretching of the case head body junction upon first firing. Since I do not have my shipment of ADG brass in yet, I thought I could get started with some measurements taken from random samples of brass. But based on the variance of measurements that I have received, I think it is best to short chamber the barrel and finish it by hand when the brass arrives.

    Thanks for the info!
     
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  6. can1010

    can1010 Well-Known Member

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    cutting the chamber to the belt will not matter because the datum measurement to the shoulder is .014 short on ADG Brass and is no way to adjust that by cutting to the belt measurement there will still be .014 case stretch. that is about normal with all belted cases that measured. I fireform mine with light load and jammed bullet to help with the problem
     
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  7. J E Custom

    J E Custom Well-Known Member

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    There are only two ways to set head space on belted cases in my opinion. With only .004 thousandths difference between minimum and maximum, I always recommend going with SAMMI .

    The other way is to use only one brand of brass and set the head space using the brass to establish the best head space for that brass.
    It still should fall in between the SAMMI minimum and Maximum but you may find that other brands will not work head spaced this way.

    As stated, once it is fired, it becomes a shouldered case unless you full length size it.

    J E CUSTOM
     
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  8. Daerider

    Daerider Member

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    Thanks for all good feedback! I went ahead and made my gauge to minimum SAAMI spec (.220") and I cut my chamber to a nice tight fit on the gauge.

    Last question - Is jamming the bullet into the lands for fireforming as effective as creating a false shoulder?
     
  9. can1010

    can1010 Well-Known Member

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    false shoulder is better if you have the expander mandrel to help create the shoulder. I have done it both ways. I just have a good load with 210 VLD jammed
     
  10. bigedp51

    bigedp51 Well-Known Member

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    Seating the bullets long and jammed is very simple, and all you do is reduce the load to the upper mid-range area.

    I have done the false shoulder method but always worried if it would stress the neck and cause early neck cracks.

    And as I stated in another forum on rimmed and belted cases you can slip a thin rubber o-ring around the rim or belt to fire form them. This works on older worn rifles with excess headspace on rimmed cases but I think the headspace limits on belted case is smaller. There you could use the small rubber bands for braces or the very small rubber bands for little girls pony tails. I say this because on a British .303 Enfield rifle at max military headspace you can have .016 head clearance.

    Below fire forming .303 British cases using 100 grain .312 pistol bullets and a rubber o-ring. When using this method make sure you grease the bolt lugs because the bolt may close firmly. Meaning your headspace and o-ring thickness will effect bolt closing effort.

    [​IMG]

    [​IMG]

    Below the rubber o-ring around the rim holding the case against the bolt face. I also have the very small pony tail rubber bands for tighter headspaced rifles. And I think the very thin rubber bands would work better on belted cases.

    [​IMG]
     
  11. J E Custom

    J E Custom Well-Known Member

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    With a belted case there is no need to use a false shoulder or jam the bullet in the lands. The belt solves all these problems. all that is necessary is to load and shoot your ammo and it will fire form without making adjustments in the powder charge to prevent over pressure.

    The only time that a reduced load is recommended on a belted case, is when forming a wildcat that calls for a large increase in powder/case capacity.

    J E CUSTOM
     
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  12. bigedp51

    bigedp51 Well-Known Member

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    With variations in belt thickness and the rifles headspace you can have as much as .012 head clearance. And with that much head clearance fire forming the case will prevent the case from stretching.

    It doesn't matter on the type method of head spacing, it is the amount of head clearance that lets the case stretch.


    [​IMG]

    [​IMG]
     
  13. J E Custom

    J E Custom Well-Known Member

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    I am way to conservative in setting head space on any cartridge so I use the go gauge for every build and shims to get the desired head space for the firearm use.

    The use of head space gauges is highly recommended in order to get proper head space and prevent problems. These gauges are tool steel and will not give false readings if used correctly, the use of any other method is not recommended.

    Most Gunsmiths will stay within SAMMI specification's, and use a go gauge to set head space. On factory or older firearms, A No Go gauge is recommended to make sure the chamber does not have excessive head space. If this gauge will allow the action to close, then a Field gauge is recommended. These gauges are normally .006 to .008 long, and if the action will close on it the recommendation is to replace the barrel and/or reduce the head space to a safe dimension. The cost of a head space gauge is around $ 35.00 dollars each and well worth the money to know for sure what your chamber is.

    On precision shouldered cartridges, I like .0005 to .001 head space. On belted cases I try to hold head space to a minimum because they already have a much smaller case body for chambering and this minimizes case stretch on initial firing in the web area. once they are fired, unless they are full length sized the become shouldered cases and no longer need the belt. with rimed cases the minimum head space is also recommended to improve case life.

    Each re-loader has his own preference on head space and as long as it is less that a field gauge the only downside is case life or inconsistent
    primer ignition. Attached is an article describing different head space requirements that might be of interest. https://www.brownells.com/aspx/learn/learndetail.aspx?lid=12555

    J E CUSTOM
     
    Last edited: Sep 30, 2018
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  14. bigedp51

    bigedp51 Well-Known Member

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    You still didn't explain why a belted case is so special that head clearance and fire forming is not required.

    It doesn't matter what stops the forward movement of the case in the chamber as a headspacing method. It is the head clearance or air space between the rear of the case and the bolt face that allows the case to stretch and thin when fired.

    And this is the very reason on a belted case you let the case headspace on its shoulder and not the belt. And with variations in case manufacture you could have as much as .012 head clearance.

    [​IMG]

    Bottom line, just because a case has a belt doesn't mean it will not stretch, thin and cause case head separations.

    [​IMG]
     
    Last edited: Sep 30, 2018