We loaded your 160grain HV 30 caliber bullet down for bush hunting in a 308 rifle and experienced much more meat damage than usual. All shots were taken between 50 and 120 metres and we are sure that we did not hit anything on the way to the animals. We recovered a bullet from a frontally shot kudu and it did not expand and was slightly bent! What is going on?
The traditional thing with loading down, is to use a heavier than normal bullet. Heavier bullets are longer than lighter bullets and you have run into a very important aspect of reloading called Gyroscopic Stability (GS). Gyroscopic Stability is the result of the correct rate of spin to stabilize a projectile of a particular length. GS is determined by the length of the bullet, the twist rate of the barrel and the muzzle velocity of the bullet. Any bullet must be stabilized to a GS factor of more than one to give stable flight. Further, it is accepted that a GS factor of more than 1.3 is required for reasonable performance in game.
With monometal bullets that shorten less on impact than jacketed lead bullets, a GS of 1.5 works even better. A long bullet such as the 308160HV needs a twist of one in ten inches to stabilize properly. The bullets no doubt tumbled on impact due to too slow a twist rate for that bullet. The fact that the bullet was bent confirms this. All bullets are designed to perform optimally at certain velocity ranges as far as expansion is concerned and the bullet must be stable enough to penetrate nose first to start the expansion. A slow, tumbling bullet will cause massive meat damage compared to a stable bullet at much higher velocity. The correct bullet for a 308 Win with a one in twelve twist is our 308 caliber 130 grain HV bullet. Twist rate is more important than speed to achieve the correct GS factor for a bullet.
The various Technical Data Pages linked from the HV, HP and FN pages have detailed information on which bullet to use for the best results in a particular caliber. Also see the International standards that govern bore and groove diameters and twist rates of standard production rifles.
GS Custom Bullets, situated in Port Elizabeth on the East Coast of South Africa, manufactures solid copper, turned, monolithic bullets for hunting and sport shooting. These bullets are used by hunters on several continents, hunting from the smallest of antelope to the largest of dangerous game, using the smooth HP bullet, as well as the more popular HV, FN and SP bullets with the patented drive band concept. GSC bullets are configured for the highest possible ballistic coefficients. SP bullets are mainly used for sport shooting. All GS Custom Bullets are moly coated.