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Old January 20, 2013, 10:50 AM   #2
Unclenick
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Join Date: March 4, 2005
Location: Ohio
Posts: 10,332
There is no single correct answer. Mag cases headspace on the belt. The SAAMI drawing gives the chamber a belt top end surface location of 0.220" to 0.227". In other words, 0.220" with a +0.007" tolerance. It gives the case belt a maximum of 0.220" with a -0.008" tolerance. Combine the two tolerances and you can have up to 0.015" difference in one gun and case brand combination to the next. And that's before you even measure shoulder height difference from one gun and case to the next and its tolerance (2.1162" -0.007" to the shoulder datum from the back end of the case head.

I am assuming in the above that by case length, you mean from the head to the shoulder datum line in the middle of the shoulder. If you mean the total length to the case mouth, that's another matter. Most of that length is increased and needs trimming due to squeeze of the sizing die returning the case to correct dimensions for general reloading (general as in to fit all chambers and not just to fit your specific chamber). You can minimize that and also shoulder datum position growth if you set the sizing die up to just bump the shoulder back a thousandth or two so the case then headspaces on the shoulder instead of on the belt thereafter.

So, what are your exact chamber dimensions and what are your exact brass dimensions before you shoot? What are you referring to as case length? If you mean the total length of the case and the amount you are having to trim off, then 0.021" is perfectly possible with the tolerances stacked against you. Also, you have a moderately high pressure round with capacity for a lot of powder. Start bumping shoulders back and stick to sub-maximum load levels and cases will grow a lot less, and brass will last a lot longer. So will your barrel. Save the full house loads for actual hunts. As that doesn't usually amount to more than a few sighters and game shots each season, they won't cut into bore life all that much in that quantity.
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Last edited by Unclenick; January 20, 2013 at 10:57 AM.
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