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Rifles, Reloading, Optics, Equipment
Reloading
Belted Magnum Head Spacing
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<blockquote data-quote="J E Custom" data-source="post: 1466855" data-attributes="member: 2736"><p>When comparing a SAMMI chamber dimension Of most Belted cases to a Full length sized case there are major size differences so I never bump the shoulder unless I neck size only. </p><p></p><p>If you neck size only, the head space is close to .000 , only brass spring back makes it possible to chamber easy. I like to head space .002 thousandths based on the brand/dimension of the belt. Once fire formed, this head space is gone and the .002 thousandths ends up as clearance in front of the belt, so a slight bump may be necessary for chambering, so from this point on, the shoulder decides what the head space is not the belt. If you full length size the belt is responsible for the head space.</p><p> </p><p>The case head to the front of the belt on a 7 Rem Mag SAMMI chamber is .220 minimum and .227 max. loaded cartridges must fall in this dimension. This clearance is set buy the gunsmith while cutting the chamber.</p><p></p><p>The cartridge dimension to the case neck junction are .009 shorter than the SAMMI chamber dimension when full length sized. so if you have add the differences in the case belt dimension and the chamber dimension to the differences to the full length sized case and the chamber dimension. It is possible to end up with up to ,017 thousandths of total case length differences.</p><p></p><p>With normal .002 thousandths head space and .002 shoulder bump and neck size only, you should end up with .002 to .004 total case length clearance.</p><p></p><p>If you full length size, you only increase the Shoulder to chamber dimension. So in my opinion it is best not to bump the shoulder if you elect to full size belted cases.</p><p></p><p>Also on the bulge in front of the belt after firing, This is caused by the chamber being to big for the SAMMI chamber dimension. Dies will size the cases back to the proper dimension, but the problem will still exist unless the chamber is re cut properly. </p><p></p><p>Just my preferred way to size belted cases.</p><p></p><p>J E CUSTOM</p></blockquote><p></p>
[QUOTE="J E Custom, post: 1466855, member: 2736"] When comparing a SAMMI chamber dimension Of most Belted cases to a Full length sized case there are major size differences so I never bump the shoulder unless I neck size only. If you neck size only, the head space is close to .000 , only brass spring back makes it possible to chamber easy. I like to head space .002 thousandths based on the brand/dimension of the belt. Once fire formed, this head space is gone and the .002 thousandths ends up as clearance in front of the belt, so a slight bump may be necessary for chambering, so from this point on, the shoulder decides what the head space is not the belt. If you full length size the belt is responsible for the head space. The case head to the front of the belt on a 7 Rem Mag SAMMI chamber is .220 minimum and .227 max. loaded cartridges must fall in this dimension. This clearance is set buy the gunsmith while cutting the chamber. The cartridge dimension to the case neck junction are .009 shorter than the SAMMI chamber dimension when full length sized. so if you have add the differences in the case belt dimension and the chamber dimension to the differences to the full length sized case and the chamber dimension. It is possible to end up with up to ,017 thousandths of total case length differences. With normal .002 thousandths head space and .002 shoulder bump and neck size only, you should end up with .002 to .004 total case length clearance. If you full length size, you only increase the Shoulder to chamber dimension. So in my opinion it is best not to bump the shoulder if you elect to full size belted cases. Also on the bulge in front of the belt after firing, This is caused by the chamber being to big for the SAMMI chamber dimension. Dies will size the cases back to the proper dimension, but the problem will still exist unless the chamber is re cut properly. Just my preferred way to size belted cases. J E CUSTOM [/QUOTE]
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Reloading
Belted Magnum Head Spacing
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