Need some help with headspacing for a .300 WBY Mag.

Discussion in 'Reloading' started by NorthernWeatherby, Jun 11, 2009.

  1. NorthernWeatherby

    NorthernWeatherby Member

    Jun 2, 2009
    I have been doing some research, but still am not quite sure I understand headspacing. I have a .300WBY mag, and would like to make sure my brass lasts as long as possible. Can anyone give pass on some of their wisdom, and at very least give me a few tips on how to take measurements for resizing, in order to make my brass last longer. As well as make my rifle a more consistent shooter.

    Thank you for any input you may have....... gun)
  2. Ridge Runner

    Ridge Runner Well-Known Member

    Dec 13, 2002
    here is what I do,
    in a 300 wea. mag, I'd either punch a 32 or 338 cal expander ball down in a fired case, then start with my die up higher than it needs to be and start resizing a well lubed case, screwing the die down as I went and closely watch the progress, when it gets close start trying it in the chamber, when the bolt will close with just a bit of resistance. screw the die down 1/16th to 1/8th turn and lock it down. the die is set for minimal headspace in your chamber.

  3. boomtube

    boomtube Well-Known Member

    Oct 8, 2007
    Using the chamber itself as a sizing gage is perhaps the best and certainly the cheapest way to properly set a sizer. Basically the way Ridge suggests, but ... the total range of "normal" headspace, minimum to maximum, is something like .007". One eight turn of a size die moves it almost exactly .0089", about 2 full thou over the total headspace allowance. That's too much!

    Suggest that once you get any sizer close limit your adjustments to one sixteenth turn (4.5 thou). Preferably a bit less if you really want the cases to fit without stretching when fired.
  4. mtelkhntr78

    mtelkhntr78 Well-Known Member

    Dec 30, 2008
    Headspacing on belted magnums can be a bit confusing. You will see many manuals list headspace on a magnum case as the distance from the top of the belt to the bottom of the case. However past experience has shown me that even with that measurement within specs, a cartridge may not chamber properly, be tight, or not at all. Reason being is that the brass may be too long at the measurment of the bottom of the case to a point on the shoulder, ie it has streached or the chamber is cut wrong. Essentially that distance is the same measurement as a headspace measurement on a non-belted case. I hope that wasnt too confusing.
    How to measure it: I recommend the hornady lock-n-load headspcae gauge. It is a little collar set up you attach to your caliper and measure from the base of the shell to the shoulder. RCBS makes a tool for measuring headspace but is cartridge specific and more expensive than the Hornady outfit. Plus the hornady tool you can read hundreds of different calibers.
    Once you determine your HS most guys that do FL size recommend bumping the shoulder back about .001", so it just barely fits the chamber. Myself I try and neck size as much as possible.
    If you are intrested in extending case life have you thought about Annealing? Many many shooters anneal becasue they believe (myself included) it greatly extends case life and improves accuracy becasue of mosre consistent neck tensions. Buffalo Bob has a real decent video on how to do it if your interested.
    Anyhow I hope that helped some.
  5. gamedog

    gamedog Well-Known Member

    Aug 16, 2007
    How can you measure or adjust headspace on a double radius shoulder?
  6. J E Custom

    J E Custom Well-Known Member

    Jul 29, 2004
    I subscribe to the KISS philosophy and on a belted case the best way I know to make the
    brass last and minimise head space is to fire the round once and neck size only from then
    on until they start getting hard to chamber.

    Your brass fits the chamber perfect and doesn't have to be re sized until it gets hard to
    chamber. Also head space is .0000 unless you size it and bump the shoulder. there is no
    reason to work your brass each time you size as long as it will chamber.

    Weatherbys have lots of free bore and this definitely improves there accuracy.

  7. brassprep

    brassprep Guest

    I agree with most of what has been posted here, however; most brass that has a neck, will not be "chamber perfect" until at least two firings. Brass has spring back. Before you settle on a true headspace (as this is the question here), fire x amount of rounds once and x twice (utilizing the already mentioned 'chamber as gauge' method) you will find that upon the second firing, you'll be much closer to real chamber size. Some HP 308 shooters believe it takes 3x to fully settle fit.
  8. woods

    woods Well-Known Member

    Jun 4, 2006
    Like some have said the first thing you need to understand is that there are 2 measurements on a belted mag case that will have a bearing on what we are talking about. Headspace as defined on this website

    SAAMI | Glossary

    The distance from the face of the closed breech of a firearm to the surface in the chamber on which the cartridge case seats. "

    which is measured from the case head to the front of the belt because the front of the belt is what stops forward movement of the case in the chamber when struck by the firing pin. However on an unbelted case headspace is the gap between case head and the bolt face when the case is pushed forward to contact at the shoulder.

    Now head clearance is the more important measurement and that on a belted case is the gap between the case shoulder and chamber shoulder

    The distance between the head of a fully seated cartridge or shell and the face of the breech bolt when the action is in the closed position. Commonly confused with headspace. "

    The Hornady Headspace Gauge

    MidwayUSA - Hornady Lock-N-Load Headspace Gage 5 Bushing Set with Comparator

    attaches to your caliper and takes a measurement on (or close to) the datum line


    it will work on a radiused shoulder as well since it is a relative measurement and will give you information about how your specific shoulder is moving.

    Using the Hornady Headspace Gauge on a belted case will let you know how much Head Clearance you have in your chamber between your new case shoulders and your chamber shoulder by keeping track of the measurments through 3 or 4 firings.

    A typical set of measurements for a 300 win mag could go something like this:

    new case - 2.253"
    once fired - 2.270" (neck sized)
    twice fired - 2.272" (neck sized)
    3 times fired - 2.2725" (crush fit)

    So the case will get tight in your chamber after a few firings and then you push the shoulder back .001" and the Hornady Headspace Gauge makes that easier to do.

    When your case gets tight in the chamber you can "headspace on the shoulder" meaning that the belt no longer stops forward movement, the shoulder does, so headspace in your belted chamber has been redefined.

    Working your brass the least possible when resizing will lengthen your brass life.