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Precision Mic

Discussion in 'Ammunition & Reloading' started by CrossHairs, Nov 23, 2009.

  1. CrossHairs

    CrossHairs Tigard Active Member

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    Got one delivered from Midway today and set about doing some measurements on the Savage 12 VLP and associated brass.

    Anyways. Measure up some brass fired from the Savage and compared it to the stuff I already full sized and de-primed (not shot in my rifle)...what a surprise, there was little to no difference in length..literally .001" over a sample of 10 rounds of pre-fired and 10 rounds of full sized. I was actually a little suspicious, so I dug out a throwaway from the trash can (got a little dented during an ejection) and measured that...0.006" over sized. So, proved that the full size pushed the cartridge back to spec, and that my headspace on the Savage also happens to be right on spec too! Who would have thought!

    Moved onto seating depth. Jammed a bullet into a casing that had already been fired and that allowed movement, but was restrictive. Popped it into the chamber and did a measurement...reliably came out with a 0.072" over OAL for the V-Max rounds I am using...then did the same with the Precision mic.....0.068" over several attempts....I guess that is a result. And proves that you can measure your chamber depth using a makeshift setup.

    What the instructions did not make clear was what you did with the number you got from the gauge! I just dropped a pre-loaded round(that was made to OAL spec) into the mic and measured the bullet seating depth relative to the gauges contact point and then took the chamber insert measurement and used the difference between the two. If I did not have the loaded round, not sure what else I would have done!? Anyone do anything different here? I'd be interested to know.
     
  2. CrossHairs

    CrossHairs Tigard Active Member

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    Lying in bed this morning I realised the answer to my own question about how the precision gauge number relates to the seating dpeth overall...! Of course, I was comparing OAL measurements with the mic offset. The actual answer is that the OAL is as a result of the measurement.

    The mic is finding the ogive of the bullet in relation to the chamber...now, you seat the bullet somewhere around .020 less than that measurement to get your actual bullet seating depth, then measure the actual OAL for future use!

    By the numbers.

    • 0.068 is the mic measurement for the chamber insert
    • So I seat my bullet so that it gives me a measurement "on the guage" of .048 (.020 offset from the lands). I do this by dropping the round into the mic and measuring it after each press.
    • when the bullet meets the gauge number, this then correspond to an OAL of 2.298". A number I note and use for future loads.

    Done, and now makes sense. I see a youtube video in the making here.

    On a final note.....took the speer bullets that I was having so little accuracy with and discovered something interesting. They are seated so that the ogive of the round is about 0.118" further from the lands than using the V-Max (according to the OAL in the book). That's a huge difference. So, when I get the chance, I'll go back around with the load tests using some new seating depths, I am sure there will be some different results.