Projectile Runout: A summary of measurements obtained from a small sample of newly loaded rounds of 6.5CM ammunition
Materials: 24 new, unfired Lapua cases, (16) Berger 130gr hybrid projectiles, (8) 122 gr Warner Flatline projectiles
Methods: Cases were full length sized in a Redding standard die with the expander and depriming stem removed. Case necks were then expanded using a 21st Century expander mandrel. Flash holes were deburred with a 21st Century tool. Case necks were turned to .013 with a 21st Century lathe, washed and dried. Cases were primed, charged and projectiles were seated in a single motion using a Sinclair micrometer die in a K&M arbor press. Using a 21st Century runout gauge, runout measurements were taken at the case neck, at the bearing surface of the projectiles near the case mouth and near the projectile tip.
Results: Bullet runout near the projectile tip ranged from .002 to .008 inches, averaging .0042. Bullet runout near the case mouth ranged from .0005 to .004 inches, averaging .0016. Case neck runout ranged from .0005 to .002, averaging .0012 inches. The tip runout to case neck runout correlation was somewhat weak at R=0.27, Bullet bearing surface to case runout correlation was slightly stronger, R=.032. The bullet tip to bullet bearing surface correlation was stronger, as expected at R=0.77.
Interpretation & Discussion: This is a small sample of cartridges and subject to the shortcomings associated with potential statistical variation. That issue aside, projectile runout in these cases is mostly due to factors other than case preparation, almost certainly due to the bullet seating procedure. The source of case neck runout was not examined, possibly related to the case sizing process, neck expansion or due to manufacturing case body/neck eccentricity or tipping. Further evaluation of these possibilities is planned. Changes in the bullet seating procedure will need to be evaluated. Previous observations by others suggest that partial bullet seating followed by 180 degree rotation of the cartridge and completion of seating may help reduce runout. Lubrication of the projectile may also be of some benefit. Perhaps honing the interior of the neck, by some as yet undetermined means might be helpful. Anything that would axially align the case neck and projectile would seem to be desirable. This might include a custom seating die and/or free floating the case for self alignment
Materials: 24 new, unfired Lapua cases, (16) Berger 130gr hybrid projectiles, (8) 122 gr Warner Flatline projectiles
Methods: Cases were full length sized in a Redding standard die with the expander and depriming stem removed. Case necks were then expanded using a 21st Century expander mandrel. Flash holes were deburred with a 21st Century tool. Case necks were turned to .013 with a 21st Century lathe, washed and dried. Cases were primed, charged and projectiles were seated in a single motion using a Sinclair micrometer die in a K&M arbor press. Using a 21st Century runout gauge, runout measurements were taken at the case neck, at the bearing surface of the projectiles near the case mouth and near the projectile tip.
Results: Bullet runout near the projectile tip ranged from .002 to .008 inches, averaging .0042. Bullet runout near the case mouth ranged from .0005 to .004 inches, averaging .0016. Case neck runout ranged from .0005 to .002, averaging .0012 inches. The tip runout to case neck runout correlation was somewhat weak at R=0.27, Bullet bearing surface to case runout correlation was slightly stronger, R=.032. The bullet tip to bullet bearing surface correlation was stronger, as expected at R=0.77.
Interpretation & Discussion: This is a small sample of cartridges and subject to the shortcomings associated with potential statistical variation. That issue aside, projectile runout in these cases is mostly due to factors other than case preparation, almost certainly due to the bullet seating procedure. The source of case neck runout was not examined, possibly related to the case sizing process, neck expansion or due to manufacturing case body/neck eccentricity or tipping. Further evaluation of these possibilities is planned. Changes in the bullet seating procedure will need to be evaluated. Previous observations by others suggest that partial bullet seating followed by 180 degree rotation of the cartridge and completion of seating may help reduce runout. Lubrication of the projectile may also be of some benefit. Perhaps honing the interior of the neck, by some as yet undetermined means might be helpful. Anything that would axially align the case neck and projectile would seem to be desirable. This might include a custom seating die and/or free floating the case for self alignment
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