Headspacing (How to).

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  • Kestrel4k
    • Dec 2012
    • 2101

    #46
    Thank you for the very good explanation, UN.
    Kestrel4k feedback thread

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    • 1deborah
      • Feb 2013
      • 293

      #47
      headspacing

      I have a straight bolt handle I'm wanting to switch with a swept back, 1903. If the headspace needs to be changed to fit the new swept back bolt, will that ruin the original bolt for use with the rifle? Best regards, Paul

      Comment

      • Unclenick
        • Nov 2010
        • 1235

        #48
        "Ruin" is an overstatement. The odds are a bolt swap will happen with the chamber still inside military specifications for both. If you go on to lap the lugs of the bolts with the receiver lugs to get a matching fit, that can open up headspace a couple of thousandths for both. Chances are, you will change the headspace of the chamber by some amount with a swap, but you want to know how much before you get concerned.

        To determine that, get a piece of 1/4" diameter cold rolled steel (CRS) rod from the hardware. These are usually 36" long. CRS is too soft to damage a bore and usually has an even softer zinc surface plating. Square one end and file it smooth and deburr the edge of the cut and, after checking no live ammo is around, close the bolt and place the cleaned end of the rod in the muzzle until it stops on the bolt face. Mark the rod where it is flush with the muzzle. Remove the rod and cut it off a half an inch below the mark and dress the cut end, too. Perfectly square is ideal. Put it back in the barrel and set the muzzle upright. Open the bolt to check the rod is in place over the firing pin tunnel and close it again (this also double-checks that no gremlin placed any live ammo inside). Use a depth micrometer to measure how far below the muzzle the end of the rod is. You can do this with the depth probe of a caliper, but it is harder to get that perfectly square unless you also have a depth measuring adapter for it. Note your measurements and without recalibrating anything, switch bolts and measure again. The difference in the measurements will tell you the difference in headspace you will have.

        If the difference isn't too big, say, a couple of thousandths as I mentioned, once you have both bolt's lugs fitting well, you can take the bolt that reduces the headspace most and have the face cut back (Dave Manson has a handtool that does this, or someone with a lathe can do it for you) to match the other bolt. Then you'll have matching headspace with both bolts for any chamber you cut for the gun. But that's not something to do to adjust a big difference. I would not want to true or cut a case-hardened bolt face back more than about two thousandths because the case may be no more than five thousandths thick if you don't have specific information to the contrary.

        Assuming a bigger difference in headspace, you may also want to ignore the error and just segregate your brass. Brass will fireform to substantially different dimensions than originally intended, as happens when parent cartridges are fired in Ackley Improved chambers to create the brass for them. Hatcher's Notebook includes a description of him cutting a '03 chamber's headspace way too deep to see what happened. IIRC, it was to 0.050" oversize, and new ammunition fired in it just fine, likely headspacing on the extractor hook. But nothing catastrophic occurred.

        Changing bolts isn't going to make a difference nearly as large as Hatcher's experiment. So, if the new bolt tightens the headspace enough that a reamer has to be applied to the chamber to lengthen it a little to get to the minimum length (desired to be sure new ammo will always chamber), then when you put the old bolt back in, the headspace will be larger. The cases will fireform to that larger size and you will be able to get a reasonable reloading life out of them by keeping the brass that was fired with old bolt segregated for use only with it. Conversely, if it's the new bolt that makes headspace too great, the same thing applies. Resize the longer brass with the sizing die not screwed down all the way or by using the Redding Competition Shell Holders selected so you only push the shoulder back a couple of thousandths and not all the way back to factory size. That is to avoid over-working the brass at each reloading cycle. Overworking will lower the number of load cycles you get before incipient head separation begins to appear.

        If the chamber has to be shortened for the new bolt by using a new barrel or setting back the old one (if this '03 is sporterized), then you may have a situation in which the old bolt becomes too tight for reliable rapid feeding (new brass may fit snuggly). At that point, you want to look at the rod measurement you made of how many thousandths of a difference the two bolts make the headspace. If it isn't too much, you may find carefully further cutting the chamber so it becomes a minimum chamber for the old bolt gives you a longer, but not excessively long chamber for the new bolt.
        --------------
        Nick

        Gunsite Orange Hat Family Member
        CMP Certified GSM Master Instructor
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        NRA Patron Member
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        • mycanoe44
          • Feb 2016
          • 475

          #49
          I purchased the Manson Reamers "Down & Dirty" headspace gauge set. It includes all 3 gauges for $70. Pretty good deal and they are very nice fit and finish.

          https://mansonreamers.files.wordpres...8-catalog2.pdf
          Political correctness is a doctrine, fostered by a delusional, illogical minority and rapidly promoted by the mainstream media, which holds that it is entirely possible to pick up a turd by the clean end.

          Comment

          • Lukester
            • Feb 2012
            • 168

            #50
            Mansonreamers review?

            Anyone out there with thoughts/opinion/review on the Manson Reamers "Down & Dirty" set?...
            They do look like a good value.

            Originally posted by mycanoe44 View Post
            I purchased the Manson Reamers "Down & Dirty" headspace gauge set. It includes all 3 gauges for $70. Pretty good deal and they are very nice fit and finish.

            https://mansonreamers.files.wordpres...8-catalog2.pdf

            Comment

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