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300 Win Mag headspace questions

Discussion in 'Gunsmithing and Repairs' started by hps1, Mar 23, 2003.

  1. hps1

    hps1 Well-Known Member

    In an effort to obtain acceptable groups with a post 64 Mod. 70, 300 Win Mag., I discovered one bolt lug was contacting only about 65% and the other about 20% or so. I lapped the lugs, stopping @ approx. 95% and 70% contact since I do not have a headspace gauge. I would guess that no more than a couple of thousandths removed from lugs, but have no way of measuring.

    I have fired Remington 150 grain factory loads with no primer setback or cratering both before and after lapping lugs.

    My handloads are sized to produce very slight resistance as the bolt is closed the last 1/4", thus headspacing off the shoulder, not the belt, and my Wilson adjustable case gauge set so that a sized or fired case is flush with the maximum headspace ledge of the gauge.

    Now for the problem. I purchased a box of Winchester 180 grain Failsafe factory ammo, which I assume is loaded rather warm, to use as a base line to measure case head expansion compared to my handloads. I dropped one of these cartridges in my case gauge and was surprised to note that it measured .028" under minimum headspace. I then checked a new unprimed Winchester case and it measured .022" under minimum. Since the Wilson gauge measures "headspace" off the shoulder, not the belt, it really gives you no idea of your rifle's headspace.

    I then miked a piece of masking tape @ .005". It took two layers to produce friction as the bolt was closed. Measuring thickness of the tape revealed it had compressed to .009" on the Failsafe and .0075 on the unprimed case.

    My question is, is .009" too much headspace to fire the failsafe ammo in this rifle?

    Thanks for your ideas on this.

  2. Badger Arms

    Badger Arms Well-Known Member

    Very safe. Factory ammo for belted magnum rounds headspaces off the belt. In fact, you can fire the gun with much greater clearance than that in your chamber. When reloading, it is advisable to headspace off the shoulder, as you are doing. Frankly, I question why you feel the need to have resistance when you are closing the bolt, but there is nothing dangerous about this. I go about a quarter to a half turn of the die further than the point at which I encounter resistance while closing the bolt. The brass doesn't last as long, however I'd rather be sure I can close it quickly for follow-up shots or dangerous game.
  3. hps1

    hps1 Well-Known Member

    Badger Arms:

    Actually, I can barely feel the case as the bolt is closed the last 1/4", probably should not have referred to it as resistance. Bolt closes easily, but you can feel it contact the case just as it closes. Get excellent case life and have never had a problem chambering a round. Besides, there aren't any bears down here in S. Texas:D . Understand why you would want a little more clearance for DG!

    Thanks for the info.


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