What is Spalling and How Dangerous is it?
When it comes to shooting steel, certain precautions need to be observed in order to protect oneself and bystanders from the lead fragments that inevitably bounce off the steel plate. These fragments, collectively, regardless of size, are referred to as “spall”. Now these fragments can be dangerous, they ‘bounce’ off the steel at considerable speed and can sometimes have enough mass to cause injury. The most dangerous form of spall is not really spall, but rather a “ricochet”. Luckily, spall is relatively easy to predict and therefore can be avoided.
When shooting at a steel plate, the spall typically deflects off the plate at around a 20-degree angle. Thus, one can imagine a “cone of danger” with the point at the bullets point of impact and spreading out from the plate at a 20-degree angle. So when adhering to the safe 180 rule at the range, shooting steel poses little to no risk because no one should be at a 20 degree angle to the target. Problems arise however when targets become damaged either through pitting or bending. This can radically change the behavior of the projectile lead compared to a flat plate. There have even been reports of nearly intact projectiles coming back directly at the shooter because of old bent targets. The pitting issue is primarily caused by the plate being shot with either too fast of a caliber, or with steel core or similarly hardened core projectiles, neither of which would have been recommended for use by the manufacturer.
Because rifle rounds contain so much more energy and velocity compared to their pistol counterparts, often steel target manufacturers list specific “minimum distances” for certain rifle calibers to be used with their targets. The reasoning behind this is twofold. First, the increased distance allows the projectile to slow down through air resistance so that it hits the plate with less energy and velocity, which will impart less damage on the target. Secondly, any fragments that come off a plate from a rifle caliber will be traveling much faster and carry much more energy than one from a pistol round. The increased distance reduces the likelihood of shrapnel hitting the shooter as well as allowing air resistance to act on the fragment reducing the amount of energy it carries and thus the damage it can cause.
So how does this apply to AR500 bulletproof vests?
The number one reason why people are concerned about spalling is that they are thinking of buying an AR500 or similar steel plate and trying to decide whether the “anti-spall” coating is worth the extra money. Anti-spall coatings are typically just truck bed-liner sprayed on very heavy. The most important consideration if you are planning on going to spend the extra money is to make sure the manufacturer applies enough of it for it to actually work. Given enough thickness, anti-spall coatings absorb near 100% of lead fragments for the first few rounds.
However, spending the extra money per plate often allows for the purchasing of a ceramic or other composite that does not have spalling issues. Moreover, the reality is that most spall will eject away from the surface of the plate at an angle such that it does not hit the user, and any few bits that do are typically trapped by the carrier itself. At the end of the day, AR500 and steel plates are the most cost effective option because they stop the highest threat rounds, repeatedly, for pennies on the dollar compared to ceramics. There is little need to worry about spall because at the end of the day, if you have to deal with spall, you just took a round center mass, you have more immediate issues that require your attention.