Bullet Expansion 101

Written by Sierra Bullets Chief Ballistician Tommy Todd

At Sierra Bullets we deal with bullet expansion on a daily basis. There are several concerns regarding bullet expansion upon impact with a media such as the bullet not expanding, complete fragmentation, limited expansion and or ricochets after impact. The major controlling factors of bullet expansion are the bullets construction (jacket thickness and core hardness), velocity upon impact, and type of media being hit.

The general rule of thumb when choosing a caliber of bullet (lets use 30 caliber for an example) the heavier bullet within that caliber will give both less expansion due to construction of the bullet and usually a lower impact velocity (150 grain hunting bullet as compared to a 180 grain hunting bullet being shot out of your favorite 308 or 30-06 rifle). One consideration of bullet expansion is to understand this impact velocity/expansion ratio. A 308 Winchester shooting a 150 grain SBT (#2125) at 2750 fps muzzle velocity will perform quite well on medium sized game such as deer. The same bullet being shot out of a 300 Winchester Magnum rifle at 3300 fps muzzle velocity will exhibit much more expansion when a deer at a matching distance the 308 Winchester above was utilized at, one would likely be better served by choosing the heavier for caliber bullet when loading cartridges at the large end of the capacity spectrum.

One myth I see in print and hear occasionally is that the bullets were “going too fast to expand” on a given animal. The laws of physics prove this myth to be false. The forces of a bullet at a velocity cause disruption of the jacket/core and start the expansion process, higher velocities/energies create more disruption and lower velocities/energies create less disruption. This has been proven through the testing of bullets in a media such as ballistic gelatin which can be duplicated and calibrated so that when you duplicate the impact velocity you get similar results and if you change the impact velocity you can track and see the difference in expansion.

Here at Sierra we offer variety of bullet weights and expansion characteristics per caliber that we manufacture. Hopefully this spectrum offers a bullet that will fit your needs. If you have any questions or concerns regarding the performance of any of our bullets or help in selecting an optimum bullet for your application feel free to contact us by phone at 1-800-223-8799 or by email at sierra@sierrabullets.com.

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1 Response to Bullet Expansion 101

  1. Pingback: Bullet Expansion 101 | Rifleman III Journal

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