- Location
- Somewhere on the Hudson Bay Coast
I thought that the subject of terminal ballistics was interesting enough to warrant further discussion, but at this point I think that its better to proceed with a new thread rather than to try to recover the old penetration thread.
Much of what follows can be found in the A-Square Manual and Kevin Robertson's "The Perfect Shot." The rest is my own observation.
Regardless of how much we invest in our rifle, or how powerful the cartridge for which it is chambered, the performance we expect on game all comes down to the bullet. We tend to agree the straight line penetration of an expanding bullet is the best way to ensure a quick humane kill of a thin skinned big game animal. An exception to the rule is the cat family whose members seem to be particularly susceptible to the shock of a violently expanding high velocity bullet. What then are the elements necessary to be present to ensure dependable bullet performance?
The first element we may think of is penetration, because without the ability to reach the vital organs, nothing else the bullet does matters very much. To a large extent the depth of penetration is determined by momentum. The bullet needs to be resilient enough to get through the skin, then begin to expand once it impacts the fluid bearing tissue. The wound volume created by the passing of the bullet is proportional to the final expanded diameter of the bullet. The construction of the bullet needs to allow it to expand but limit that expansion to ensure that the bullet’s dimensions remain linear. The industry norm is that 2/3rds of the bullets shank needs to remain un-expanded to ensure straight line penetration. The bullet must be stable to ensure deep penetration, but without rotation around a linear axis, given the varying densities inside a game animal, the bullet would be prone to following an erratic path. This is called Conservation of Angular Momentum and is the foundation of the performance of expanding bullets.
Losing mass is detrimental to penetration, and the bullet once fully expanded must remain intact despite the broad range of impact velocities that might be encountered over the useful range of the bullet. As the bullet expands the center of gravity moves towards the nose, and the nose heavy attitude combined with the rotational velocity keeps the bullet straight and stable despite tissue of varying density it comes in contact with, including bone. The wide diameter of nose section of the bullet keeps the bullet enveloped within a shockwave that displaces soft tissue, and while the bullet is supersonic it only impacts with bone at super-sonic velocity. The rotational speed of the bullet is not effected during the super-sonic passage of the bullet through soft tissue, and only when it’s forward progression becomes subsonic does the friction from surrounding tissue begin to effect the rotational velocity, which is little reduced from the moment it exited the muzzle of the rifle.
Much of what follows can be found in the A-Square Manual and Kevin Robertson's "The Perfect Shot." The rest is my own observation.
Regardless of how much we invest in our rifle, or how powerful the cartridge for which it is chambered, the performance we expect on game all comes down to the bullet. We tend to agree the straight line penetration of an expanding bullet is the best way to ensure a quick humane kill of a thin skinned big game animal. An exception to the rule is the cat family whose members seem to be particularly susceptible to the shock of a violently expanding high velocity bullet. What then are the elements necessary to be present to ensure dependable bullet performance?
The first element we may think of is penetration, because without the ability to reach the vital organs, nothing else the bullet does matters very much. To a large extent the depth of penetration is determined by momentum. The bullet needs to be resilient enough to get through the skin, then begin to expand once it impacts the fluid bearing tissue. The wound volume created by the passing of the bullet is proportional to the final expanded diameter of the bullet. The construction of the bullet needs to allow it to expand but limit that expansion to ensure that the bullet’s dimensions remain linear. The industry norm is that 2/3rds of the bullets shank needs to remain un-expanded to ensure straight line penetration. The bullet must be stable to ensure deep penetration, but without rotation around a linear axis, given the varying densities inside a game animal, the bullet would be prone to following an erratic path. This is called Conservation of Angular Momentum and is the foundation of the performance of expanding bullets.
Losing mass is detrimental to penetration, and the bullet once fully expanded must remain intact despite the broad range of impact velocities that might be encountered over the useful range of the bullet. As the bullet expands the center of gravity moves towards the nose, and the nose heavy attitude combined with the rotational velocity keeps the bullet straight and stable despite tissue of varying density it comes in contact with, including bone. The wide diameter of nose section of the bullet keeps the bullet enveloped within a shockwave that displaces soft tissue, and while the bullet is supersonic it only impacts with bone at super-sonic velocity. The rotational speed of the bullet is not effected during the super-sonic passage of the bullet through soft tissue, and only when it’s forward progression becomes subsonic does the friction from surrounding tissue begin to effect the rotational velocity, which is little reduced from the moment it exited the muzzle of the rifle.
