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Rifles, Reloading, Optics, Equipment
Gunsmithing
Light primer strikes
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<blockquote data-quote="Unclenick" data-source="post: 2398117" data-attributes="member: 106107"><p>Overseating primers used to be a more common problem. A lot of the original Speer primers were made with a compound that became too brittle when it dried and it would crack during reconsolidation and fail to fire. These days, at least for common brands like CCI and Federal, you don't have a brittle compound in the cup. However, reliability research by Naval Ordnance at Indian Head (NOIH) showed it is best not to compress past 0.004" deeper than where the anvil feet contact the floor of the primer cup. Olin and Remington always allowed for up to 0.006", but NOIH found that went too far for best reliability.</p><p></p><p>If you have a depth micrometer, you can measure your primer pocket depth. A caliper depth stem at the back of the beam is hard to use accurately if you don't have a <a href="https://www.amazon.com/Fowler-Warranty-52-565-700-0-Attachment-Caliper/dp/B00B5HQ8WG/ref=sr_1_2?crid=UOPGPBV02RKE&keywords=caliper+depth+base&qid=1641754398&sprefix=caliper+depth+base%2Caps%2C81&sr=8-2" target="_blank"><span style="color: rgb(41, 105, 176)">T-bar depth adapter</span></a> to keep the beam square with the case head. To use it most easily, mount it on a digital caliper. Hold it against the case head and extend the proper to touch the bottom of the primer pocket floor. Push the caliper zero button. Next, place the primer you will seat in the caliper jaws and measure its height. There will normally be a number that is zero to minus 0.002" on the caliper. This is how far below flush with the head the primer will be when its feet just barely kiss the floor. Subtract another 0.003" from that number to get the distance below flush the primer will be when it has that much reconsolidation or compression of the compound or bridge set. Now zero the caliper on a flat surface like a piece of plate glass. Seat the primer and measure and add seating pressure until the caliper reads the right reconsolidation value below flush.</p></blockquote><p></p>
[QUOTE="Unclenick, post: 2398117, member: 106107"] Overseating primers used to be a more common problem. A lot of the original Speer primers were made with a compound that became too brittle when it dried and it would crack during reconsolidation and fail to fire. These days, at least for common brands like CCI and Federal, you don't have a brittle compound in the cup. However, reliability research by Naval Ordnance at Indian Head (NOIH) showed it is best not to compress past 0.004" deeper than where the anvil feet contact the floor of the primer cup. Olin and Remington always allowed for up to 0.006", but NOIH found that went too far for best reliability. If you have a depth micrometer, you can measure your primer pocket depth. A caliper depth stem at the back of the beam is hard to use accurately if you don't have a [URL='https://www.amazon.com/Fowler-Warranty-52-565-700-0-Attachment-Caliper/dp/B00B5HQ8WG/ref=sr_1_2?crid=UOPGPBV02RKE&keywords=caliper+depth+base&qid=1641754398&sprefix=caliper+depth+base%2Caps%2C81&sr=8-2'][COLOR=rgb(41, 105, 176)]T-bar depth adapter[/COLOR][/URL] to keep the beam square with the case head. To use it most easily, mount it on a digital caliper. Hold it against the case head and extend the proper to touch the bottom of the primer pocket floor. Push the caliper zero button. Next, place the primer you will seat in the caliper jaws and measure its height. There will normally be a number that is zero to minus 0.002" on the caliper. This is how far below flush with the head the primer will be when its feet just barely kiss the floor. Subtract another 0.003" from that number to get the distance below flush the primer will be when it has that much reconsolidation or compression of the compound or bridge set. Now zero the caliper on a flat surface like a piece of plate glass. Seat the primer and measure and add seating pressure until the caliper reads the right reconsolidation value below flush. [/QUOTE]
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