Post by bradshaw on Dec 2, 2019 8:42:14 GMT -5
The great belted magnums don’t need a belt to hold up their pants. Starting before any of us were born, the belt was used to connote case strength and promote power. As far as a bolt action is concerned, the belt is just another rim. To use the belt to headspace the cartridge allows all sorts of dimensional sloppiness from ammunition to chamber. A bottleneck case must be headspaced between CASE HEAD and DATUM LINE----midpoint of shoulder.
A tapered case inclines to grow forward at firing and at resizing. One way to check this is to measure a case before and after sizing, and after firing. Brass flows forward, not rearward. The head of a case is harder than the shoulder and neck, with less elasticity. The hardness is a necessary part of the “head gasket.” To anneal a casehead would invite a blown primer pocket or brass flow into the boldface. In Hatcher’s Notebook, Julian Hatcher described the headstamp as the final step in hardening the casehead. Unlike commercial brass, military brass was not tumbled to remove annealing discoloration at the shoulder.
Neck sizing works great for some cartridges, but my results haven’t been universally cheery. For bottleneck cases in handgun silhouette, I neck sized everything until a trip through the full length die became mandatory, at which time the case was re-trimmed (and neck reamed if necessary). My silhouette loads were not Rocks & Dynamite, so brass lasted a long time.
NECK SIZING works, proving the neck stays straight and the round exhibits no runout.
PARTIAL RESIZING with full length die allows for a whisper of drag on closing the bolt. Unless the chamber and sizing die are a close match, proper bolt operation may require very close to full length sizing. Partial sizing can cause the shoulder to move forward as the wall is squeezed. Bolt operation is the arbiter of partial sizing.
David Bradshaw
A tapered case inclines to grow forward at firing and at resizing. One way to check this is to measure a case before and after sizing, and after firing. Brass flows forward, not rearward. The head of a case is harder than the shoulder and neck, with less elasticity. The hardness is a necessary part of the “head gasket.” To anneal a casehead would invite a blown primer pocket or brass flow into the boldface. In Hatcher’s Notebook, Julian Hatcher described the headstamp as the final step in hardening the casehead. Unlike commercial brass, military brass was not tumbled to remove annealing discoloration at the shoulder.
Neck sizing works great for some cartridges, but my results haven’t been universally cheery. For bottleneck cases in handgun silhouette, I neck sized everything until a trip through the full length die became mandatory, at which time the case was re-trimmed (and neck reamed if necessary). My silhouette loads were not Rocks & Dynamite, so brass lasted a long time.
NECK SIZING works, proving the neck stays straight and the round exhibits no runout.
PARTIAL RESIZING with full length die allows for a whisper of drag on closing the bolt. Unless the chamber and sizing die are a close match, proper bolt operation may require very close to full length sizing. Partial sizing can cause the shoulder to move forward as the wall is squeezed. Bolt operation is the arbiter of partial sizing.
David Bradshaw