Results 1 to 17 of 17

Thread: Bumping shoulders

  1. #1
    Join Date
    Jul 2010
    Location
    Virginia
    Posts
    169

    Default Bumping shoulders

    I own a Winchester semi auto .308 Win and an M1A. I have civilian .308 Win and 7.62x51 NATO brass. Read lots about shooting / reloading civil ammo in military rifles and visa versa. Lots of folks seem concerned about excessive head space, sloppy chambers on military weapons (on purpose) and tight SAMMI specs on civilian rifles. Many speak of bumping the shoulders back around .002 when reloading.

    My question is...if I full length resize both 7.62 and .308 Win brass, shouldn't both reloads be acceptable for shooting from either rifle?

  2. #2
    Join Date
    Jan 2010
    Location
    central Ks
    Posts
    3,466

    Default

    The answer to your question is "Yes", with a qualifier.

    Qualifier is "Brass life may be reduced somewhat."

    This depends entirely on how much difference there is in the chamber's headspace dimentions.

    What I would do is generate a half dozen pieces of fired brass from both rifles, marked for which one.
    Attempt to identify which rifle drives the shoulder fwd. farther when fired.

    If it is too hard to tell, pick a rifle (#1), full length size the brass, BUT work with adjusting the resizing die to only JUST reach the shoulder and push it back just barely enough to get the brass to re-chamber in that rifle. Absolute minimum resizing/shoulder moving.

    Now see if it will chamber in the other rifle.

    If it does, set that brass aside and back off the die, and repeat the process with the other rifle. You likely have already found the "tighter" headspaced rifle.

    When you have just barely got brass to fit rifle #2, try it in rifle #1.

    Once you find the "longer" rifle, set your brass to just barely fit in the shorter rifle. This way, firing in IT will strain the brass (stretching) the least, and firing in the other rifle will stretch it as little as necissary, but it will stretch more than the first rifle will let it.

    Then you just have to make sure the ammo is compatible to the M1's gas system. Mil. rifles get designed to work around a very narrow cartrige profile (147gr bullet at arround 2800fps). Civ. rifles get much more "adaptable" gas systems. The difference in pressures betwen NATO and Civ .308, is little enough as to be pretty pointless. It's 2,000psi, at 60,000psi. 3%

    Stretch happens when the firing pin drives the loose unfired case fwd. into the shoulder and holds it there while the primer detonates. The resultant firing pressure locks the case walls to the chamber, jammed against the shoulder, but the head of the case is too thick to "swell and stick" so it pushes back against the bolt face, stretching the brass just ahead of the head web.

    My hunting rifle is a late 60's Browning BAR, .308, love that rifle. I almost exclusively use GI brass in it.
    Last edited by Oldstuffer; 11-10-2010 at 06:27 PM. Reason: Addition

  3. #3
    Join Date
    Jan 2009
    Location
    Eastern England
    Posts
    1,232

    Default

    Much of what you have said ref .308 verses 7.62x51 is correct but not to be taken too much out of context. It is quite correct that chamber tolerences on military weapons are often more generous than commercial rifles to enable them to function reliably with ammo from different NATO countries. The main difference between commercial and military brass is case wall thickness, milsurp brass generally has thicker case walls to cope with chamber tolerences in weapons from more than one country. This results is reduced volume inside a milsurp case as compared with commercially produced .308 brass, something to take into account when working up loads, due to possible pressure issues. If you are satisfied that the headspace in both rifles is within tolerence, full length sized and trimmed reloads should function in either rifle.
    Once fired, the brass will be fireformed to that particular rifle and I would keep the brass for the rifle that fired it and neck size only from then on. I would probably keep the milsurp brass for the M1A and the commercial brass for the Winchester (always assuming you have enough of each) If you are intending to use load data for top end loads for each rifle using both types of brass, remember that some .308 commercial loads can produce pressures of 60000 psi (against 7.62 Nato, 52000 psi) the smaller volume milsurp case could increase this even further.
    ukrifleman

  4. #4
    Join Date
    Sep 2008
    Location
    Southeast Louisiana
    Posts
    15,068

    Default

    Quote Originally Posted by ukrifleman View Post
    Much of what you have said ref .308 verses 7.62x51 is correct but not to be taken too much out of context. It is quite correct that chamber tolerences on military weapons are often more generous than commercial rifles to enable them to function reliably with ammo from different NATO countries. The main difference between commercial and military brass is case wall thickness, milsurp brass generally has thicker case walls to cope with chamber tolerences in weapons from more than one country. This results is reduced volume inside a milsurp case as compared with commercially produced .308 brass, something to take into account when working up loads, due to possible pressure issues. If you are satisfied that the headspace in both rifles is within tolerence, full length sized and trimmed reloads should function in either rifle.
    Once fired, the brass will be fireformed to that particular rifle and I would keep the brass for the rifle that fired it and neck size only from then on. I would probably keep the milsurp brass for the M1A and the commercial brass for the Winchester (always assuming you have enough of each) If you are intending to use load data for top end loads for each rifle using both types of brass, remember that some .308 commercial loads can produce pressures of 60000 psi (against 7.62 Nato, 52000 psi) the smaller volume milsurp case could increase this even further.
    ukrifleman
    More of what UK said. After fireforming any cases to your chamber, the need to bump the shoulder is not there. Neck sizing is then only really needed. And you can use milsurp cases, after fireforming to the civi weapon, remembering they will probably need a reduced charge.
    It would be best to keep your cases sorted. Civi brass for the civi weapon, and milsurp for the M1A. Keep them in containers that are marked clearly soo's you make no mistake. In a survival situation, well, you ain't in that yet.
    If a man has nothing greater to believe in than himself, he is a very lonely man.

    I reckon so. I guess we all died a little in that damn war.

    And in that time when men decide and feel safe to call the war insane, take one moment to embrace those gentle heroes you left behind.
    Quote Originally Posted by MEJ1990TM View Post
    Well, all right. Maybe just this once.

  5. #5
    Join Date
    Dec 1969
    Posts
    6,606

    Default

    Failure to full lenght resize for a M14/M1a is false economy IMHO .. once fired 7.62x 51 isn't that expensive or hard to come by and should be good for 4 or 5 reloads FL resized. You start slamming tight fitting cases into a semi auto and you are asking for problems.

    Here is what the Pros say about reloading for the M14/M1a http://www.m14.ca/reloading/14_loading.pdf
    This post has been edited , vetted, and archived by the NSA.

  6. #6
    Join Date
    Jan 2010
    Location
    central Ks
    Posts
    3,466

    Default

    Quote Originally Posted by AmmoSgt View Post
    Failure to full lenght resize for a M14/M1a is false economy IMHO .. once fired 7.62x 51 isn't that expensive or hard to come by and should be good for 4 or 5 reloads FL resized. You start slamming tight fitting cases into a semi auto and you are asking for problems.

    Here is what the Pros say about reloading for the M14/M1a http://www.m14.ca/reloading/14_loading.pdf
    Yes indeed.

    My BAR will not tolerate one of it's fired cases neck-sized only, period. It HAS to be F/L resized in order to chamber under nothing but spring pressure. It doesn't have to be drastically shortened at the shoulder, BUT, it DOES have to be forced back a thou or two to get the bolt to close.
    A jammed 90%-closed bolt on an autoloader is a mother to get open again.
    A hammer helps.

    Autoloaders will not force a chamber-sized case into the chamber like a bolt action will.
    Last edited by Oldstuffer; 11-12-2010 at 05:21 AM.

  7. #7
    Join Date
    Dec 1969
    Location
    BumbFK
    Posts
    1,719

    Default

    Here's a previous thread wherein I listed the NRA Match Load Data safe for M1A/M-14 and 308 Garands. It gives M80 equivalent loads for five different powders and 150 grain bullets.
    http://forums.gunboards.com/showthre...ght=m80%20ball

    The caveat about dropping reloads in mil cases 2 grains still applies. Also, reloading commercial cases will achieve case head separations sooner than mil cases when shot in mil spec chambers. Still, full length resize if you want reliable chambering in an autoloader. Stick to powders between IMR 3031 and IMR 4064 in Garands and M1As to save over-accelerating the oprod and bolt. I have been using 41 - 42 grains of IMR4895 with 168 grain Sierra HPBT (this is often referred to as "The Load" in Highpower) for M1a and 308 Garands for decades.

    EDIT: Use a primer pocket uniformer tool and check every round to ensure you primer is seated below the case head when reloading for the M1A. High primers are suspected of being the cause of some out-of-battery firing disasters (often erroneously called "slam fires") It is also commonly recommended one use less sensitive or "harder" primers such as CCI, Wolf, and Winchester avoiding "softer" primers, i.e. Federal is often considered a "soft" primer and avoided for service rifles.

    And here's an article with references which dispels much of the decades old myths that continue to be pounded out on keyboards:
    http://home.comcast.net/~ehorton/The...762%20NATO.pdf
    Last edited by Ordtech; 11-12-2010 at 02:38 AM.
    How many psi in a CUP?

  8. #8
    Join Date
    Jul 2010
    Location
    Virginia
    Posts
    169

    Default

    Thanks to everyone for the enlightening information !

  9. #9
    Join Date
    Jan 2010
    Location
    central Ks
    Posts
    3,466

    Default

    Quote Originally Posted by ukrifleman View Post
    ........................................... .308 commercial loads can produce pressures of 60000 psi (against 7.62 Nato, 52000 psi) the smaller volume milsurp case could increase this even further.
    ukrifleman
    Your note of 'Nato 52,000PSI', should read 52,000CUP

    52,000Copper Units Pressure is, in this cartrige, a bit over 60,000PSI.

    60,000+ PSI, vs. 62,000PSI.
    Not enough difference to matter one whit.

  10. #10
    Join Date
    Dec 1969
    Posts
    8,202

    Default

    I am impressed. This short thread is the most definitive on the subject yet seen anywhere. Board members really boxed this subject up tightly.


  11. #11
    Join Date
    Dec 1969
    Posts
    858

    Default

    I have also been told that about .002" is about right for a M1A or M1 match rifle.

    For anything less than competition, I can't see why you would just not full-length resize. The gains with minimum resizing would be slight, if any at all and there is the cost of the case headspace micrometer to consider along with the substantial time factor involved with carefully checking the sized cases. If you end up with a case that did not bump the shoulder enough, you could have problems as AmmSgt point out. An out of battery discharge could really ruin your day.

    There should be a gain is case life with minimum resizing. This sounds good at first, but consider as an alternative that for volume firing, you'd be better of loading the ammo down a few notches on the pressure scale. That should give much better brass life and really, there is no reason to shoot full pressure loads if you are just punching paper out to about 300 yards.

    So to the original question yes, the full-length sized cases should work in both rifles. The cases fired in the rifle with the bigger chamber will likely stretch more and need to be retired earlier.
    There is always a well-known solution to every human problem--neat, plausible, and wrong.
    H. L. Mencken

  12. #12

    Default

    I had trouble loading for my M1A match rifle till I sprung for a Small Base sizer die. Full length resizing with a set of standard dies just didnít do it.

  13. #13
    Join Date
    Jan 2010
    Location
    central Ks
    Posts
    3,466

    Default

    Quote Originally Posted by Ranger Z View Post
    I had trouble loading for my M1A match rifle till I sprung for a Small Base sizer die. Full length resizing with a set of standard dies just didn’t do it.
    That does happen sometimes.

    My .308 BAR has never hickupped with GI 7.62 brass once-fired and re-worked by std. Hornady Full-Length dies, BUT, that's my rifle.
    A rifle with a very minimum-spec-cut chamber may well need a S.B. die.

    I usually advise buying std. die untill you actually discover that they won't size small enough. $25 "saved" just assuming a person needs S.B. dies is equally bad as the "waste" the other way I suppose.

  14. #14
    Join Date
    Jul 2010
    Location
    Virginia
    Posts
    169

    Default

    ..."but consider as an alternative that for volume firing, you'd be better of loading the ammo down a few notches on the pressure scale. That should give much better brass life and really, there is no reason to shoot full pressure loads if you are just punching paper out to about 300 yards".

    "I had trouble loading for my M1A match rifle till I sprung for a Small Base sizer die".


    Good thoughts both...thanks. I have a Redding SB die on the way, and I'm going to drop my loads down in small amounts, until the M1A shows signs of degradation to cycling.

  15. #15
    Join Date
    Dec 1969
    Location
    BumbFK
    Posts
    1,719

    Default

    Quote Originally Posted by Oldstuffer View Post
    Your note of 'Nato 52,000PSI', should read 52,000CUP

    52,000Copper Units Pressure is, in this cartrige, a bit over 60,000PSI.

    60,000+ PSI, vs. 62,000PSI.
    Not enough difference to matter one whit.
    +1 Been telling the world that for years but Granny and Bubba's dog's girlfriend's cousin are still telling people fairy tales.
    How many psi in a CUP?

  16. #16
    Join Date
    Jul 2010
    Location
    Virginia
    Posts
    169

    Default

    I had trouble loading for my M1A match rifle till I sprung for a Small Base sizer die. Full length resizing with a set of standard dies just didn’t do it.

    I bought a case gage (their spelling) from Wilson. It gives you an exact point for the shoulder, so you can set your die. I used the gage and put 120 reloads in it. These were full length resized w/ a Lee die, which I own many sets of. These were 7.62x51 once fired cases shot through an M60. 12 rounds did not meet the gage tolerences. I pulled them. I'm still scratching my head over the fact that all the cases went through the same resizer die set in the same position, but the shoulder on 12 were out of tolerence. I now am using a Redding SB resizer, and still run some brass through it a couple times to get the shoulder position right.

  17. #17

    Default

    Not all brass is exactly the same. Some will spring back farther than others when you size them. If you are trying to run really close tolerances this can happen. Your choice is to either accept the lost cases, size just a little bit more, or try annealing your cases first and see if that helps.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •