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Long Range Hunting & Shooting
Interpreting SAAMI Specs
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<blockquote data-quote="gregmark24" data-source="post: 2720988" data-attributes="member: 121785"><p>In attempting to use a Hornady headspace comparator gauge to verify SAAMI specs, I find that I'm confused with the specs. Take the 6.5 Creedmoor as an example. The SAAMI spec from base of the case to the 0.400" dia point on the shoulder is 1.5438" - 0.0070". Let's say it is on the long end at 1.5438". The next illustration shows the chamber, with the spec from breech to that same 0.400" dia point as a minimum of 1.541" and a maximum of 1.551". Let's say it is on the shorter side at 1.541". Doesn't this indicate that, worst case, a case at 1.5438" is longer than the close-bolted chamber of 1.541" by 2.8 thousandths?</p><p></p><p>As a separate note, I think I've figured out how to get from the comparator gauge to actual lengths. The full length of my inserted gauge (red cut-out to silver colored insert face) is 2.004". However, there is a chamfer between the measured face of that gauge to the actual 0.400" hole. I THINK that chamfer is 0.010". So, in my case, to get from the measured comparator length (say, for a spent 6.5 CM case, is 3.538"), take the 3.538", subtract 2.004", and add back 0.010" for the chamfer loss, and get a true measurement of 1.544". Factory match grade ammo is 3.536" on the comparator--minus 2.004 plus 0.010" = 1.542, and within spec. I need to bump the head back by 0.002"</p></blockquote><p></p>
[QUOTE="gregmark24, post: 2720988, member: 121785"] In attempting to use a Hornady headspace comparator gauge to verify SAAMI specs, I find that I'm confused with the specs. Take the 6.5 Creedmoor as an example. The SAAMI spec from base of the case to the 0.400" dia point on the shoulder is 1.5438" - 0.0070". Let's say it is on the long end at 1.5438". The next illustration shows the chamber, with the spec from breech to that same 0.400" dia point as a minimum of 1.541" and a maximum of 1.551". Let's say it is on the shorter side at 1.541". Doesn't this indicate that, worst case, a case at 1.5438" is longer than the close-bolted chamber of 1.541" by 2.8 thousandths? As a separate note, I think I've figured out how to get from the comparator gauge to actual lengths. The full length of my inserted gauge (red cut-out to silver colored insert face) is 2.004". However, there is a chamfer between the measured face of that gauge to the actual 0.400" hole. I THINK that chamfer is 0.010". So, in my case, to get from the measured comparator length (say, for a spent 6.5 CM case, is 3.538"), take the 3.538", subtract 2.004", and add back 0.010" for the chamfer loss, and get a true measurement of 1.544". Factory match grade ammo is 3.536" on the comparator--minus 2.004 plus 0.010" = 1.542, and within spec. I need to bump the head back by 0.002" [/QUOTE]
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