TERMINAL BALLISTICS HEAVIER BULLETS ARE BETTER RIGHT?

Hexagon Ammunition’s Paul Bradley delves into the science of bullet weight and terminal ballistics, equipping retailers with insights to guide customers in selecting the most effective ammunition for their needs.

The age-old debate on bullet weight… Most of the time people will automatically pick the heaviest option when given a choice. A bullet has one purpose, to deliver energy to a target. There are several variables which affect how much energy is delivered – velocity, mass, terminal form factor, and terminal stability. When people promote heavier projectiles with little qualification, they usually consider only two of the variables – mass and velocity. They assume velocity will be the same or similar for both projectile weights. In the real world we are bound by some regulations and physics. Let’s use a 308 Winchester round as an example.

A 110gn projectile travelling at 3200fps produces about 2100 Joules of energy on a 200m target. Of course, we have to stay within safe pressure limits, so a 168gn projectile will have a much slower maximum velocity at around 2600fps. This will give us 2400 Joules of energy at our 200m target. That is not a great gain in energy considering the vast weight difference, but it is a gain. This is because velocity plays a bigger role than mass when it comes to delivering energy. If you could choose to double the velocity or the mass, you would always achieve a better yield doubling the velocity.

On top of that, we could add that the heavier projectiles probably have a higher BC and thus less velocity decay. This equates to higher retained velocity at longer distances. At 800m our theoretical 110gn bullet has now slowed to 1007fps and will deliver 336 Joules. Meanwhile, our 168gn bullet is travelling at 343m/s, which gives it the edge on both velocity and mass. It nearly doubles the energy on target at 644 Joules.

Given the example above, it is no wonder people choose heavier bullets and, if one were only allowed to choose FMJ, then it would probably be the right choice. This is why bullets used by the military have slowly gained weight over the years. They are bound by the Hague convention and physics, so they can only increase bullet mass. The remaining variables of terminal form factor and terminal stability are generally not options for them.

Our energy on target calculations are based on the bullet actually stopping in the theoretical target. FMJ or HPBT type projectile will likely not stop in a target if we were hunting animals. This is why they are not used for hunting. Our above calculations would then need to change considerably. Both of those rounds would pass straight through, retaining a large portion of their velocity and thus a large portion of energy as well. Retained energy post target is energy that failed to be delivered…

Hunters are able, and in fact should, always use projectiles which are designed to deform or fragment. The deformation/ fragmentation increases the size of the wound channel, and it slows and hopefully stops the projectile in the soft tissue. It does this by either increasing its surface area or shedding mass, both of which make it less suitable to travel through any medium (including air). Stopping the bullet in the target causes all the energy to be transferred to the target, which is exactly what we want to achieve. This is where projectile weight becomes an issue. Bullets can deform or fragment due to force acting on them. The amount of resistance they meet at the target combined with the projectile’s velocity may be great enough to produce deformation/fragmentation. This will depend on the amount of projectile material present and the type of material. In this case, a projectile with more mass will require more resistance to produce deformation when comparing the same material specification.

One of the reasons lead has been such a popular core material is both its density and its malleability. It requires only a small amount of force before it begins to deform or break up. Copper is far less malleable. Even a lead-cored projectile will fail to deform substantially if the target lacks enough resistance in comparison to the bullet’s mass.

So, what does this mean in the real world of the hunter? It means that hunters have a responsibility to assess their likely target and select the correct weight of projectile in context of material spec. This is why bullet manufacturers offer so many types and weights to the hunter. It is not just a marketing play. If I were to select a 165gn projectile made of C109 Copper to harvest a small deer it would likely pass straight through. The wound cavity would be small. The bulk of the projectile’s energy would be retained as velocity post target. Not only would this be unethical to the target animal it would carry additional risk due to ricochet. In this case, I would select a much lighter option with less material to be moved. A 90 grain projectile made of the same material hitting the same small deer would likely deform or break apart, depending on the design.

So why do heavier projectiles exist in the hunting world? For larger species. A 90gn projectile hitting a much larger target animal will still deform or break up but this may occur too quickly, leading to lack of penetration to the vital organs. Again, this would be an unethical shot. There are no projectiles that are ideal for all species because of the variables we have discussed. There may be some choices which will suit a fairly wide variety of species but never all. We demonstrated this to a team of enthusiastic sales professionals on a recent demonstration day and hunt at Norma Sweden. Many of the sales people were unsure which hunting rounds they should suggest to their customers. They told us that many customers would make the selection based on price. In a perfect world, the cheapest option could fulfil all tasks adequately, but sadly this is not the case. An ethical hunter must also be an educated hunter. This has become more important as we venture into the use of lead-free projectiles and when we consider increased critique of hunting in general. As sales people, we have a responsibility to provide this education when a customer asks for help. Manufacturers are normally more than happy to provide all the relevant data; we must ensure it is passed on.

We’d love to hear your thoughts on this topic, e-mail your views over to editorial@twsgroup.com