Headspacing for 7mm stw?

Discussion in 'Gunsmithing' started by shephem, Apr 24, 2010.

  1. shephem

    shephem Member

    Messages:
    21
    Joined:
    Jan 14, 2006
    What is the best way to check the headspace when I chamber for the 7mm STW? I was told by a gunsmith that I do not have to set the barrel back, but this is where I get confused. How will I check the headspace since the are both belted mags and would use the same gauge.

    Also if anyone has a mag go gauge for sale let me know I need one for another project also.
     
  2. shortgrass

    shortgrass Well-Known Member

    Messages:
    1,992
    Joined:
    Mar 31, 2010
    Are you asking about re-chambering a 7mm Rem. Mag, to 7mm STW? If this is the case, I would set the barrel back at least a half a turn. When any re-chambering is done the end result would not to have any 'shadows' of the old chamber left in the new chamber. By setting back you would be cutting with all the STW reamer. You didn't mention the maker of this rifle. really need more info for a detailed answer. There's no way around not having a set of gages, IMHO.
     
    Last edited: Apr 24, 2010

  3. shephem

    shephem Member

    Messages:
    21
    Joined:
    Jan 14, 2006
    The gun right now is a Weatherby Vanguard 7mm rem mag. I was told by two smiths that there is no need to set the barrel back since the STW is biger than the 7mm mag. If I did it this way then the go/no go gauges will not work.

    Also I have a go gauge on its way from midway.
     
  4. Loner

    Loner Well-Known Member

    Messages:
    599
    Joined:
    Apr 14, 2010
    The stw is bigger from the front end of the belt forward. You will get a clean new
    cut without setting the barrel back , Just look up the case dimensions for the two
    cartridges. As all belted cases they headspace off the belt the first firing and then off
    the shoulder if you neck size.
     
  5. dirtball

    dirtball Well-Known Member

    Messages:
    764
    Joined:
    Jan 18, 2007
    You NEED to set the barrel back, I would suggest a full turn. Right now the GO gauge you ordered WILL "go" in your 7mm Rem Mag. If you do not set the barrel back you will not be able to tell how deep the 7 STW reamer is in the barrel until it is too far and the you will still have to set the barrel back.
    The problem is ALL .535 base belted cases headspace off of the belt not the shoulder.
    Dave
     
  6. shephem

    shephem Member

    Messages:
    21
    Joined:
    Jan 14, 2006
    Thanks for the replies. I am going to set it back now, I just need to decide how much. It will be a 1/4 turn or a full turn.
     
  7. Loner

    Loner Well-Known Member

    Messages:
    599
    Joined:
    Apr 14, 2010
    The stw belt is the same depth of .2200 but the case is .002 wider from in front of the
    belt forward. How would He not know?
     
  8. dirtball

    dirtball Well-Known Member

    Messages:
    764
    Joined:
    Jan 18, 2007
    What happens to the cartridge case design ahead of the belt has no bearing on the headspace gauge of a belted case. The gauge only measures the depth of the belt.
    Virtually all cartridges from the 257 Weatherby thru the 416 Rem Mag are .532 base dia and are 513 just ahead of the belt.
    PTG lists ALL belted mags as being interchangable. See line 2.
    http://www.pacifictoolandgauge.com/pdf/headspace_gauge_interchangeabilty_chart_12_15_08.pdf
    If you look at a headspace gauge for a belted case you will see that they are much smaller ahead of the belt that the case would be.
    PTG Headspace Go Gage 6.5mm STW - MidwayUSA

    Dave
     
  9. tackdriver10

    tackdriver10 Well-Known Member

    Messages:
    136
    Joined:
    Nov 17, 2009
    You would want to go one full turn, so that the engraving ends up in the same place. It will make things so much simpler when you set the headspace. I'm not sure what thread pitch on the weatherbys are because I have yet to do one myself. However if it is 16 TPI, (just like the remmys) then that is only .0625 of material that you would remove from the end of the barrel. Not very much at all. I don't think you will notice any difference in cosmetics or in velocity.
     
  10. Loner

    Loner Well-Known Member

    Messages:
    599
    Joined:
    Apr 14, 2010
    A 257 weatherby is .511 in front of the belt as are 7mm and 300wm and many others. The 300 H&H being the parent case. The STW is off of an 8mm case which is .513.
     
    Last edited: Apr 25, 2010
  11. Loner

    Loner Well-Known Member

    Messages:
    599
    Joined:
    Apr 14, 2010
    To Add, most barrels (if not all) are not straight, the curve is usually indexed up by
    the gun builder. You want that to remain the same if possible. I have had barrels not
    turned a full turn because of other constraints and everything was fine, but that is not always the case.
     
  12. shortgrass

    shortgrass Well-Known Member

    Messages:
    1,992
    Joined:
    Mar 31, 2010
    The case for custom barrels. I just can't see putting money for rechambering into a production barrel, I just wouldn't be satisfied. As far as the caliber designation, I think I would rather have none at all verses the wrong one on there. Picture this! The 7mm Rem. Mag. will chamber in the 7mmSTW, and fire! I don't want to be the shooter or the guy that did the work in that case. If there's no caliber designation at least it says (to me, anyway) that 'something' has been altered, investigate before firing (all barrels should have the proper caliber designation imprinted or engraved on them). I measured a barrel tenon on a Howa 'take-off' barrel, 1.018" dia. , which translates to 25.85mm (a strange number) x 1.5mm. (most likely 26 X 1.5mm).The barrel would advance .0591" per complete turn. The STW really needs a 26" barrel and most factory built 7mm Rem. Mag.'s have 24"barrels. As for the headspace being the same, yes, it is. In theory it sounds good to just "run that STW reamer in until the part that cuts the belt starts to cut. Unfortunately, in practice, you have gone too far by then and the bolt will close on the 'NO-GO' gage and you will be setting the barrel back to correct for proper headspace. If you did stop cutting in time, would the old chamber be completely removed by the STW reamer. Maybe, maybe not. I can't see a manufacture taking the time to install a barrel to its 'curve'. Time and skill cost money, and they need to sell as many rifles as they can for as much profit as they can (they are publicly traded companies). I think they are more interested in profit and liability than quality these days.( my JGS chamber prints show both the 7mm STW and the 7mm Rem. Mag. to be the same diameter, .513", just ahead of the belt)
     
  13. J E Custom

    J E Custom Well-Known Member

    Messages:
    7,309
    Joined:
    Jul 29, 2004
    I would recommend setting the shoulder back 1/4 turn to place the barrel ID under the stock
    and re stamp the new caliber correctly.

    This will also help clean up the old chamber and throat better.

    The head space should be set buy the smith and if you want to buy a go gauge they are only 35.00
    to 40.00 dollars and can be used on most standard belted magnums. ( a good tool to have ).

    This is also a good time to have the action trued if it has not been done before assembly and head
    spacing.

    J E CUSTOM
     
  14. Loner

    Loner Well-Known Member

    Messages:
    599
    Joined:
    Apr 14, 2010