This Sika spiker was taken with a .243, using a 100 grain Sierra GameKing. Muzzle velocity was approximately 2860fps, impact velocity 2324fps. Inline shots to the spine certainly stop light bullets fast. Total penetration was around 6-8". It takes either more bullet weight or a change in bullet design to initiate full through and through penetration with such shots. Not that it was needed though, a spine shots are instant killers.
You can see that the GK bullet is of a frangible design but with a somewhat stout jacket (stouter than the A-Max). It is identical to the Nosler Ballistic Tip in this regard. Cross body penetration of the .243 GK is usually quite adequate on game of this size (approx 60kg / 130lb), the bullet either exiting or coming to rest against the offside hide. The GK is frangible throughout the calibers but a hunter can get caught out, such as expecting full fragmentation when using a 180gr .308 GK on a spiker. In such instances, not enough resistance is met on impact resulting in delayed expansion/ fragmentation. Exit wounds can be up to .75" but killing is slow. Matching bullet weights to game weights is the key, as it is with all bullet designs.
Pointing out the bullet path. The hunter was slightly above the spiker, the animal facing directly away, quite a tricky shot at 220 yards in field conditions.
Extent of wounding
The recovered projectile, the fingers held inline with the point of arrest.
The recovered fragmented projectile.