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Minimum headspace on a M1A. Would this work?

Discussion in 'Handloading and Reloading' started by Fatelvis, Dec 7, 2012.

  1. Fatelvis

    Fatelvis Well-Known Member

    Please tell me if this would work to size for minimum headspace in a M1A.:
    1) Fire a cartridge with gas system turned off.
    2) Neck size and reload catridge.
    3) Fire again with gas system turned off.
    4) Run this case up into your press using the #10 Redding Comp shellholder.
    5) Screw a Forster Shoulder bump die (w/o bushing) into press until the case's shoulder touches the die's shoulder.
    6) Lock die in place using die's lockring.
    7) Replace #10 shellholder with #8 shellholder.
    8) Install proper bushing.
    9) Size case.
    Would this be a good way of sizing a case, and giving .002" headspace in a given M1A? Please let me know of any problems, tips, or corrections you can see. Thanks!
  2. fguffey

    fguffey Well-Known Member


    F. Guffey
  3. fguffey

    fguffey Well-Known Member

    There are methods and or techniques that would allow a reloader to determine the length of a chamber from the bolt face to the shoulder of the chamber without firing a case, I do not know of a reloader that has the skill, methods and techniques, but is it a safe bet there are a few that can.

    I have no clue why you would choose the #10 Redding competition shell holder, I do not know why you would choose any Redding competition shell shoulder by # (number), I have a set for belted cases (#6), I paid $5.00 for the set of 5, anything I can do with the Redding Compitition shell holders I can do with a feeler gage, the advantage goes to the feeler gage, I have 10 options between .000 and +.010, Redding competition shell holders offer 5.

    I would suggest you determine the length of the chamber first (before firing), fire formers fire first, if I was a fire former I would fire a case then measure the length of the case from the head of the case to the shoulder of the case with a tool that is erroneous called a head space gage, something like a Hornady/Sinclair head space gage, after measuring the length of the case from the head of the case to the shoulder/datum compare the length with the length of the case before it was fired from the head of the case to its shoulder/datum, if you did not measure the length of the case before firing, start over. the difference ion length between the unfired case and fired case measures the effect the chamber had on the case when fired.

    Then there is that problem with not knowing the length of the chamber, the L.E. Wilson case gage is a datum based tool, when a case is inserted, or as ‘THEY’ say ‘dropped in’ the case protrusion indicates the length of the case from the datum to the head of the case, problem, it is up to the reloader to furnish the ‘rest of the tool’, most use their thumb nail, I use a straight edge, I lay a straight edge across the head of the case then measure the open gap between the straight edge and bottom of the case gage, again, if the case had been measured before firing the difference in the two readings would indicate the effect the chamber had on the case when fired.

    I have a set-up table, using the set-up table is an option and is not as awaked as using the straight edge, I set the case up on the set-up table then place the Wilson case gage on the case. After setting the gage on the case I measure the gap between the table and bottom of the case gage using a feeler gage. Meaning the long case is holding the case gage off the table, all that is required if me is to determine ‘how much’.

    Using the #10 shell holder is to assume the chamber is .010” longer than the minimum length factory store bought case from the bolt face to the shoulder of the chamber. In the perfect world the difference between the chamber length and minimum length cases is .005”. Remember, the standard shell holder deck height is .125” the deck height of the Redding Competition shell holders increases the deck height .002” for each number, as in #1 has a deck height of .127” etc., the #5 has a deck height of .135”, except my set, 3 of the shell holders are off by .001”.

    Again, I convert go-gages to go-to infinity gages.

    Correlation, not fair, there is a correlation between my chambers and my dies. my dies restore cases to minimum length/full length sized cases, the difference in length between my unfired cases and fired cases correlates to the adjustment I make when sizing a case as in adjusting my dies to and or off the shell holder, back to Redding Competition Shell holders, Redding Competition shell holders offer 5 options, with the perfect chamber that is go-gage length the reloader would use the standard shell holder to size a case that is .005” shorter than the go-gage length chamber. A reloader would use the #2 shell holder to size cases that are .001” shorter than than the perfect go-gage length chamber.

    Confusing. Chambers are not perfect, chambers come in various length from the bolt face to the shoulder of the chamber, Redding Competition Shell holders can be used to size cases if the reloader knows the length of the chamber, again, I have an Eddystone M1917 with a long chamber, it is .002” longer than a field reject gage, not a problem, I form 280 Remington cases to fit my M1917 chamber, I shim the sizing die off the shell holder .014” when forming/sizing 280 Remington cases, my formed cases are .002” shorter than the chamber when measured from the usual places.

    BUMP? No I rectified it as in altered, the 280 Remington shoulder was erased, it did not bump, it did not move, part of the shoulder became part of the neck and part of the case body became part of the case shoulder, when finished I had a new shoulder, the old shoulder did not move, I formed a new shoulder, I have no ideal when bump stops and forming/sizing begins, again, bump sounds like an accident.

    F. Guffey
  4. Fatelvis

    Fatelvis Well-Known Member

    My thinking was that using a twice fired case from the chamber with the shoulder of the bump die locked down to it, would represent my chamber size.
    I thought that using the #10 shellplate (I should say +.010" shellplate)to set the die, and then using the +.008" shellplate to size the brass, would accurately set the shoulder back .002". Reguardless of the terminology, the shoulder would be "reformed", and give me the wanted .002" headspace, correct?
  5. fguffey

    fguffey Well-Known Member

    I measure the length of the chamber first, I then transfer that measurement, then there is fire forming, I can fire a case, measure the length of the case from the head of the case to the case shoulder then transfer that measurement to the press when adjusting the die to the shell holder.

    If you use the +.010 Redding Competition shell holder when sizing a case you are adding .010” to the length of the case, in the perfect world of chambers and minimum length cases that is .015” added to the length of the case because you are raising the die off the deck height of the shell holder .015”, back to the standard shell holder, the standard shell holder has a deck height of .125”, when the die is screwed down to the shell holder with the proverbial additional 1/4 turn (down) the case is sized to minimum length/full length sized, for those that can correlate, that is .005” shorter from the case head to the shoulder than a go-gage length chamber, again, there is a chance the shoulder of the case is not contacting the shoulder of your die with the additional deck height of .015”.

    Standard shell holder with out the proverbial 1/4 additional turn, cases sized with the full length sizer die adjusted to the top of the shell holder (top above or below) will size cases to go-gage length.

    I size cases for short chambers, the short chamber sized cases are from .012” to –.001'” shorter than a minimum length sized case, it is possible to size cases for short chamber by raising the deck height, everyone else grinds the top of the shell holder to lower the deck height.

    F. Guffey
    Last edited: Dec 7, 2012
  6. 243winxb

    243winxb Well-Known Member

    I would guess brass springback would eat up that .002" Try for .006" if you must. But i would forget the Forster Shoulder bump die. When the bump die first became available, i emailed Forster. Its possible to bulge the shoulder if you "bump" to hard or alot. A bulge in the shoulder would not be good for an auto M1A.
  7. Edarnold

    Edarnold Well-Known Member

    From my viewpoint, the question is: Why? You are going to great deal of trouble to produce reloads that may cause your M1A to malfunction. Whatever theoretical accuracy gains your proposed technique would be negated by the first instance of an oversized round wedged in the chamber with the bolt half locked.

    If your rifle's accuracy does not satisfy you, work on the rifle: there many tuning tweaks that can be applied to the M1A that don't adversely affect the reliability.

  8. Swampman

    Swampman Old Fart

    Are your current handloads sufficiently accurate the they will consistently outshoot FGMM?
    If they are, maybe this will make them better, if not, work on other factors.

    If you're just looking for increased case life consider a Schuster adjustable gas plug.

    If you're going to go for headspace that tight, I recommend that you uniform your primer pockets and make SURE your primers are seated deeply enough.

    Just my opinion, but the M14 was designed as a battle rifle, I consider weapon or ammo mods that compromise that basic premise to be unsound. If you need quarter inch groups, get a Remington or Savage bolt gun.
  9. Fatelvis

    Fatelvis Well-Known Member

    I am looking primarily to extend brass life, and maybe tweak a little more accuracy out of the load. I had a Match M1A previously that I had case head seps after just two loadings, and although I have a different rifle now, I really would like to get more life out of my cases in this rifle! Lol
  10. Swampman

    Swampman Old Fart

    Consider trying the Schuster, I'm no expert, but I think a lot of the damage done to brass by the M1a is caused by the bolt starting to open too quickly, especially with hot loads.

    I do know that adding a suppressor can make even middle of the road loads destroy brass in fairly short order.

    Using the Schuster allowed me to dial in the gas system so that the rifle no longer tore up brass with the can on.

    I ended up taking it off because it adversely affected reliability when switching between different loads or when removing or replacing the can.

    If you tend to use the same load most of the time, it should do great.

    Anymore if I want to use the can, I just turn off the gas system and use it as a straight pull.
  11. W.E.G.

    W.E.G. Well-Known Member

    Buy a proper micrometer headspace gage.

    The RCBS Precision Mic is my recommendation.


    Buy a box of Federal Gold Medal .308 Winchester ammo.
    Measure the base to shoulder dimension of the rounds with the Precision Mic tool.

    Size your brass to match the same measurement you got with the Precision Mic.

    I guarantee you will find that measurement to be within 0.001" of 1.628"

    Don't get fancy or cute with sizing brass that will be fired in a semi-auto rifle.
    Size it to the SAAMI dimension, or expect to have a lot of issues.

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