When picking self-defense ammunition, what’s the prime attribute to look for? A lot of people would tell you it’s velocity, and with the popularity of +P ammunition as carry ammo for both police and civilian carriers it would appear to be a good one.
Or is it bullet design? There are design attributes of expanding ammunition.
Why Do Hollow Points And Other Types Of Self-Defense Ammunition Expand?
When it comes to self-defense ammunition, the jacketed hollowpoint is the reigning king of the day. In times past, the lead semi-wadcutter hollow point and the soft cast lead bullet before that were the dominant rounds of the day. Each is known for expanding when they enter soft tissue, causing both a larger wound cavity to form but also slowing to a stop inside the target.
How does this work?
When the bullet enters a soft-tissue target, the pressure on the front of the bullet increases dramatically. Since a jacketed hollow point has an exposed core, more pressure is exerted on the rim at the tip of the bullet because that’s the part that hits first. The lead core peels outward, deforming the jacket and causing the trademark “mushrooming” of expanding ammunition.
Previous forms of carry ammunition like the LSWCHP and soft-lead bullets of the 19th century would likewise deform, though they didn’t necessarily mushroom as dramatically as quality JHP ammunition of the present day.
So, it is therefore the case that the desired performance of defensive ammunition is produced by the hydraulic pressure of soft tissues. However, as anyone that’s done much ammo testing or looked at ammunition tests knows, not every hollowpoint actually expands when it hits a target.
What Affects Expansion?
The mechanism by which expansion happens is hydraulic pressure. What affects how it acts on the bullet when it enters the target?
First is velocity. If a bullet doesn’t work at a slower velocity, making it go even faster can make it work or make it work better, which is why +P ammunition became so popular. After all, barely anything happens to your bumper if you run into a bollard at 5 mph or less. Ram into the same bollard at 50 mph and your car will be totaled.
However, the other aspect is design of the bullet itself, in terms of materials, construction, and geometry. Arguably, it’s more important.
Frontal surface area is crucial. You see, for the hydraulic pressure to work on a bullet and produce expansion, there has to a good amount of real estate for it to push on, which causes the core to peel back rather than continuing through the material. This is why “wide mouth” hollowpoints expand more reliably than narrow hollow points.
Metallurgy is important in this respect; the softer the lead core, the more easily it will expand. The harder the jacket, the less easily it will be peeled back.
This is also why .45 ACP JHP rounds (the “flying ashtrays”) are thought to expand more reliably than 9mm hollowpoints. This was certainly the case for many years, though modern 9mm hollowpoints, even standard pressure rounds, are now no worse than their larger counterparts.
Other aspects of construction also make, pardon the pun, an impact. For instance, a reverse taper – where the jacket is thicker at the tip than the base – combined with a cut in the jacket can result in drastic expansion under pressure. Posts in the core of the bullet or polymer inserts can also aid in expansion.
Bonded bullets, which attach the jacket to the core by one of a number of methods, prevents separation or fragmentation. Provided otherwise good bullet design, expansion is controlled and reliable. This has made bonded ammunition very popular in both defense and hunting applications.
In short, velocity helps as a higher velocity impact will amplify the force of the impact, but a good bullet will expand at almost any velocity, let alone at high velocity for caliber – so you don’t necessarily need a +P or +P+ round for it to perform reliably at the moment of truth. That said, if your carry gun feeds +P rounds well and you shoot your preferred overpressure ammunition well, by all means keep carrying it.