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Thread: New 300 Win Mag

  1. #1

    New 300 Win Mag

    Just picked up the new toy and have a bit of an issue with it which I'm hoping the reloading experts on here can assist with...

    Basically it is incredibly difficult to close the bolt with a round in the chamber. It can be done but sometimes this is a two handed job giving concern that the bolt handle might snap. It is doing this with Remington, Winchester and Federal brass.

    The builder has said that it is a minimum headspace chamber to induce accuracy and that once fired the brass will be fine. Not quite sure I follow this and am concerned that when I start full length sizing the brass will just go back to this incredibly tight fit. The builder has said he can increase the headspace in 1 thou steps to make it easier to close but obviously I don't want to affect the accuracy if possible.

    Just wanting to know what the experts think - please don't respond if all you are offering is that "this isn't right and send it back...etc"

    Many thanks

  2. #2
    Are these new factory ammo or resized cases? If they are reloads I would try some factory ammo which should feed without an issue. If they are reloaded cases that have been fired in another chamber you could try full length sizing to see if they fit but if not try new cases. Has the smith tried with a go and no go headspace gauge. Presumably the rifle has been proof tested so therefore should have a SAAMI spec chamber.

  3. #3
    it would be interesting to measure the bullet before chambering a round then remove it and measure it again. My guess is that you're forcing the bullet back into the case when closing the bolt.
    the removed bullet itself will probably be marked from the rifling too

  4. #4
    What did you ask the rifle builder to build? Did you ask for a specific reamer to be used? I've certainly got the distinct impression from some of the work I've had done that there's no guarantee factory ammunition will load in the resulting custom chamber. If I asked for factory ammunition to be used, then I'm fairly sure I'll get the chamber made with a bigger reamer. At some point I'm getting a 308 Win chambered and it will need to accept factory ammunition without issue and I'll supply some samples of factory ammunition when the work is being done.

    In summary, what did you specify and was that specification met?



  5. #5
    I would check my cases for signs of excessive pressure.

  6. #6
    Being a belted case it should headspace on the belt, nothing to do with the bullet or the shoulder. If it wont close on a factory round then I suspect that it needs a bit more work on the chamber.

  7. #7
    Thanks for the responses - a few interesting points! In terms of some responses:

    Yes this is happening with factory rounds
    I don't think this is being caused by the bullet/col as the pressure being used to close would push that back into the case
    There was no specific spec given for the chamber. As such I assumed I would get something that would take standard saami cartridges and this is my fear when I start reloading for this cartridge that I'll have the same problems.
    Not dealt with belted cases before.

    I'm gong to load a couple of fired cases to saami col over the next couple of days to see what happens.

    Many thanks

  8. #8
    Quote Originally Posted by biffa View Post
    The builder has said that it is a minimum headspace chamber to induce accuracy ....
    can't get my head around this

    from what you have described the builder has deliberately built a chamber that has a VERY short headspace between belt rim and bolt face
    No Way can it be binding on the lands or the shoulder unless he has cut a very very short throat or he has screwed up the belt to breech dimension
    I am struggling to understand how this is going to "induce accuracy"

    has he built a belted rifle before?
    ideally you want a throat that can accomodate a long 210+gr bullet of over normal mag length (you won't get a 208gr or 210gr VLD to seat deep enough on the powder charge that gets them up around 28-2900fps as they a very long. 208gr AMax are 39mm long!)

    To be honest I would get it reamed out to accept ALL factory ammo and then headspace off the shoulder when you reload
    Two handed bolt closure is a reason to return to builder IMO. No chamber should be cut this tight

    I am assuming the fired brass will have been fireformed to the new headspace dimension and that the bolt lifts normally? post some pictures of the brass especially of the area just north of the belt.
    Any brightening rings?

    The problem I found running reloads headspaced off the belt came when the cases were marginally undersized (and I mean marginally) when load developing with warmish loads I got partial or full case head separation.
    IMO The anchoring effect of the belt on the case head increases the separation effect

    size to fit the chamber with the shoulder touching or very very slightly off the chamber/shoulder

    I find the 300WM a very accurate round. It doesnt need a great deal of help
    ALL my load development groups were inside or around an inch at 100yds and it produced two clear accuracy nodes where all but one of the holes from the group overlapped
    this was with 208gr Amax and 3 separate powders from low to high charges
    Last edited by bewsher500; 08-05-2014 at 12:25.

  9. #9
    Quote Originally Posted by bewsher500 View Post
    ....To be honest I would get it reamed out to accept ALL factory ammo and then headspace off the shoulder when you reload....
    +1 and then get it re-proofed.



  10. #10
    SD Regular johngryphon's Avatar
    Join Date
    Aug 2010
    Victoria Australia Sambar country.
    Weld an extension pipe onto the bolt handle so you can have extra leverage to get it closed more easily.
    Dont dither,take the shot!

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