Help/advice on 300 Win Mag headspace

Discussion in 'Big Stuff--7mm, 30 Cal, .338+' started by Bigguy1951, Dec 12, 2014.

  1. Bigguy1951

    Bigguy1951

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    I have started having some difficult extraction, as in headspace problems, with my 300. Primary extraction just doesn't seem to quite get the job done on about 1/2 of my reloads. I have been able so far to just use my hand to knock the bolt back and remove the casing. All of my loads are 1-2 grains below listed maximums for the bullet/powder combination and show no primer flattening or ejector marks. Got a headspace gauge from Sinclair and what I have found surprises me. The difference between the average of 10 recently fired cases and 10 fully resized cases is .014. Way beyond the .002 to .004 I was expecting. The brass I am using is Federal brass that came from factory loaded ammo. I still have some of that ammo and measured 10 of them as well. My recently fired brass is .024 longer on average than the unfired brass. Is this common? Is it a problem I should be concerned with or should I just reset my sizing die to bump the shoulder back .002-.004? By the way the gun is a 1995 Winchester Model 70 (with boss) and accuracy is very good.
     
  2. CatShooter

    CatShooter Guest

    The belted magnums have two headspaces - the belt, and the shoulder - which are you talking about. If you set the FL die to push the shoulder back, you will have problems.

    Shooters of belted cases use the shoulder for headspsace after the first firing (which uses the belt).

    Make sure you are not shoving the shoulder back when you are sizing the case.

    I shoot three belted cases and they are not a problem.
     
  3. Bigguy1951

    Bigguy1951

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    I am measuring headspace on the shoulder. My real concern was that the chamber may have been cut a little long, hence the extra growth.
     
  4. CatShooter

    CatShooter Guest

    First, You didn't say how you were measuring the headspace... that would be helpful.

    If your reloads are 1 to 2 grains below your book's "maximums"... you can be sure that they are 1 or 2 grains OVER some other book maximums.

    The load manuals are just guide lines. With most calibres, and especially with belted cases, you can be "up there" and not get ejector marks... flattened primers are 90%+ from headspace, and are not a reliable sign of pressure.

    The 300 Winchester Magnum has two headspaces. The "official" one is the belt, the one we are interested in, is the shoulder.

    The case belt is from 0.212" to 0.220".
    The case shoulder (0.420" line) is from 2.263" to 2.270"

    The chamber belt is from 0.220", to 0.227"
    The chamber shoulder is from 2.2691" to 2.2791"

    With belted magnums, the cases uses the belt to headspace on for the first firing, then ("IF" we are smart) it uses the shoulder to headspace on when we reload it.

    Worst case = the belt and shoulder of the case are minimum - 0.212" and 2.2691"...

    ... and the chamber is maximum, 0.220", and 2.2791".

    When the primer fires, the case moves forward 7 thou and locks in place. Then the shoulder blows forward to fill the rest of the space.

    When pressure peaks, the back of the case is pushed back to the bolt, and your case has already starts to stretch at the web.
    If you Full Size the case with an average die (RCBS, etc), it will force the shoulder all the way back to minimum of 2.2691". And the cycle starts.

    This is why your fully sized cases showed so much difference compared to un-sized fired cases.

    Keep in mind these facts of life.

    1 - standard FL dies are cut to give minimum shoulder headspace, and to reduce the body "some", but not back to minimum.
    2 - Factory (or average gunsmith) cuts chambers anywhere in the range, and most often on the long side.

    When I shoot cases for the first time, I lightly oil the cases to keep them from suffering the original stretch in front of the web.

    Then I neck size until the cases are sowing resistance to bolt closing - then I bump the shoulders back, THE MINIMUM amount so the bolt closes with acceptable effort.

    There is no reason to keep bumping 0.002", when the shoulder keeps on growing - if you are bumping on a case that is not filling the chamber headspace, then you are just adding more stretch, every time you fire it.

    Don't start bumping until you start to feel bolt closing resistance... then only a few thou.
     
  5. Bigguy1951

    Bigguy1951

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    Thank you for taking the time to do the very detailed reply. Clearly I have some cases at each end of the spectrum, long and short, and some in between. I will sort the cases and only bump the cases that are at maximum. As for measuring the length, I am using a Sinclair bump gauge.
     
  6. MagnumManiac

    MagnumManiac

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    There is nothing abnormal with either your brass or your chamber, .024" clearance for the shoulder is about in the middle for most 300 chambers. Just bump the shoulder .002" and you should be good.
    BUT, if you are getting sticky bolt lift, check to see if you're getting ANY cratering on the primers, this can cause sticky bolt lift.
    What rifle is it?


    Cheers.
    :D
     
  7. CatShooter

    CatShooter Guest


    Why "bump the shoulder 002"... from what reference?? He already has a hellovalot of headspace and case stretch, he doesn't need more.

    He needs to get his process under control

    He has a 1995 WInchester M-70
     
  8. Road_Clam

    Road_Clam

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    I recently started reloading .300WM, and asked the same questions. You will get severall different methods of resizing. After all my questions and research I ended up with a process of first just shoot the pi$$ out of your ammo and aquire your rifle's specific "fire formed" casings. I checked my rifle's headspace using a factory round and masking tape and came up with about .006" clearence. My next step was to obtain a accurate fireformed sized dummy "go" casing for my rifle for easy repeatability of sizing casings. I did this using the "soot" method at the shoulder to obtain my die's resizing "zero" at the shoulder. I then used my trick Larry willis h/s gauge and set my die to push the shoulder back an additional.002 as other's suggest. I also use Larry's magnum collet die as needed. Looks like about every third reload I need to collet size the base of the casing. I had some sticky bolt retraction issues prior to my above described method, but now with the above stated method of sizing, even at max loads my casings eject perfect every time. I'm no expert reloader, but after all my trial and error, this seems to be a method that's working real good for me. Here's LW's site, have a read :

    http://www.larrywillis.com/
     
  9. Dgd6mm

    Dgd6mm Silver $$ Contributor

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    Just got a .300 WM. and I am going to start reloading for it soon. I may have to pick some brains here on die set up among other loading info for it. I've never owned a belted cartridge before. :D
     
  10. Dave in WI

    Dave in WI Runs with scissors

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    I have an adjustable case gauge for 300 wm. I think it is Wilson? It's like other case check gauges, except you can adjust it with a case fired from your chamber and use it to set your sizing die.

    Wilson pt#CGA300WN
     
  11. MagnumManiac

    MagnumManiac

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    The reason is because the cases WILL NOT chamber unless he does.
    Unfortunately, most people don't understand HOW headspace is set up for belted cases, you sound like one of those. As soon as the shoulder moves forward, the belt, which controls headspace on unfired cases, will move rearward taking up that space, then, because the shoulder is now .026" forward, the case body will move forward when resized, moving the shoulder forward, causing hard chambering and extraction, as the OP has discovered.
    BTW, the shoulder moves forward easier than the brass at the web, no stretching takes place in this area on the first firing, it's subsequent firings and sizing that causes the stretching, especially if excessive sizing is taking place.
    Have been using belted magnums for more than 25 years, both hunting and competition, .002" shoulder bump is what's required, neck sizing doesn't work.
    I would suggest a Redding body die, neck bushing die and comp seater, even the Forster set up with bushings is a good one, and some sort of headspace measuring tool. I have the RCBS Precision Mic and Hornady caliper style gauges.

    Cheers.
    :-\
     
  12. gzig5

    gzig5

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    The brass is being over sized and shoulder being set back too much. The shoulder should be set back 3-5 thousandths of an inch from the max fired dimension for best brass life. Then the brass fits YOUR chamber. I don't think there is anything wrong with your rifle.

    I'm surprised nobody else suggest it but your sticky extraction may be coming from the brass expanding just in front of the belt. This area of the case is not touched be the resize die. You might want to look into the Magnum Collet Die at this link.
    http://www.larrywillis.com/

    After hearing how much you've been pushing the shoulder back on that brass, I would strongly suggest you pitch that brass in the recycle bucket and start with a fresh batch.

    Be aware that new belted mag brass commonly has excess "headspace" to the shoulder, new out of the box. I just check new vs fired 7mag Winchester and 300mag Nosler brass. Win grew .025" on first firing and the Nosler grew .015". There is nothing wrong with either rifle. That's just the way they make belted brass. It is short to the shoulder when new. I will set the dies up to push the shoulders back between .002-.004". That's on the long side and the cases should headspace on the shoulder now. This will significantly reduce the chances of a premature head separation from setting the shoulder back excessively. One 7mag brass I'm temped to neck up to .308 and then down, forming a false shoulder to headspace on for that first shot. Not sure if that would help the case web, but it shouldn't hurt.
     
  13. 'Freak

    'Freak Gold $$ Contributor

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    How many firing(s) is it taking to blow the case’s shoulder forward enough to finally reach the chamber’s shoulder?
     
  14. CatShooter

    CatShooter Guest

    HUH???

    "Unfortunately, most people don't understand HOW headspace is set up for belted cases, you sound like one of those. As soon as the shoulder moves forward, the belt, which controls headspace on unfired cases, will move rearward taking up that space, then, because the shoulder is now .026" forward, the case body will move forward when resized, moving the shoulder forward, causing hard chambering and extraction, as the OP has discovered.
    BTW, the shoulder moves forward easier than the brass at the web, no stretching takes place in this area on the first firing, it's subsequent firings and sizing that causes the stretching, especially if excessive sizing is taking place."


    This is the most convoluted explanation of what goes on in a chamber, that I have ever heard. It defies logic and well known internal ballistics....

    I currently load for 3 belted cases... a 264-WM and 300-WM in Remington actions, and 375-H&H Whitworth on a Mauser action, and have loaded for 5 others (3 Remingtons and 2 Winchester M-70s) that I no longer own any more.

    You need basic understanding in how cases behave when firing.

    When a standard case is fired, the primer forces the case faward until the shoulder comes to a stop at the shoulder of the chamber.

    If the case and chamber are dry, the case walls grab the chamber, and the pressure forces the case head back to the bolt face, causing it to stretch at the web - damage that cannot be repaired.

    If the case or chamber walls have oil or cleaning solvent on them (are "WET"), then the case walls cannot get a grip on the chamber walls, so under pressure, the whole case slides back, and the case does NOT stretch in front of the web. That is a good thing (so says Martha Stewart).

    ---

    When a belted case is fired for the first time, the belt controls the head space (much better than a standard case, to closer tolerances)... and forward motion of the case from the force of the primer is stopped by the belt, NOT the shoulder.

    When the case is stopped by the belt, the gas is expands the case body, and the case walls grab the chamber walls, and if the case and chamber are dry, the case sticks to the chamber.... it does not move from this point on.

    Then and the head (and belt) are pushed back until it hits the bolt face (stretching the case in front of the web), and the shoulder blows forward like a Gibbs or Ackley case would, until it hits the chamber shoulder, and then it springs back a few thou after the bullet leaves and pressure drops to zero.

    If he case and/or chamber are wet with oil or bore cleaner, the case slides back when the powder develops pressure, and the shoulder expands forward to fill the chamber, and then recedes back a few thou from "spring back".

    At that point the case does NOT stretch, it fits the chamber perfectly, with a few thou to spare from spring back.

    If you rechamber the fired case, it goes in fine, because there is still a fair amount of space between the shoulder of the case, and the headspace of the chamber... that is what "spring back" is.

    And this is why people that are having custom dies made from fired cases require the case to be fired and neck sized 3 or 4 times before sending it in... so it will have expanded to the longest length possible and be almost chamber length.

    If you have problems refeeding a fired case into a belted chamber, you have other problems - I have yet to need to FL a case for any of my three belted cases.
     
  15. lloydx2

    lloydx2

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    The problem is when you fire the first time You have already started the cycle of head spacing off the belt
    The solution is to reload first firing and jamb the bullet into the lands with federal (soft) primers. Then you are supporting the case at the base (against the bolt) and the shoulder of the bullet (in the lands). This lets the shoulder blow forward more completely before the belt stops it. But no worries. You can buy a die (ring) that just sizes the area in front of the belt. B Pike sells them on this website. You might need the ring periodically even if you are head spacing off the shoulder.
     
  16. seymour fish

    seymour fish

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    Grease the factory loaded rounds with Imperial die wax on case body. Fire. You now have a well fire-formed case. When your reloads give more than just a light crush-fit, bump shoulder half a thou at a time until crush fit just barely past undetectable, and continue loading/shooting.
     
  17. CatShooter

    CatShooter Guest

    I use G-96 in an ink pad, and roll the cases for ALL first firings so there is "0" case stretch, and from that point on, I adjust cases for a slight crush and they last forever.
     
  18. seymour fish

    seymour fish

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    Cat, "Honest men generally arrive at the same conclusion". LOL. Eventually, Seymour
     
  19. CatShooter

    CatShooter Guest

    Do you have the website for B Pike???
     
  20. Toby Bradshaw

    Toby Bradshaw Gold $$ Contributor

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    pbike257. He's a member here. He doesn't have a website. Makes great tools, though.

    https://www.youtube.com/watch?v=-QW-5npXJKs
     

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