Wednesday, July 25, 2018

Velocity Matters

I received a call from a friend a few days back asking about some loads for a new AR platform he had just finish. Seems he built a 300 Blackout rifle with a suppressor and wanted some sub-sonic loads to hunt hogs with. When I told him they won’t work much past 25 feet the discussion got lively. Suppressed subsonic loads in the Blackout are all the rage right now, and in certain circumstances they are great, but for hog hunting?

The problem is the lack of velocity. Simply stated, bullets are velocity driven; meaning they get their energy from the velocity they travel at. In short, the faster a bullet  goes the more energy it possesses upon impact. The problem is, my friend wanted to use a 200 grain bullet at 1050 feet per second. At that speed the bullet only carried 467 foot pounds of energy at 50 yards – hardly enough to effectively kill a large adult hog. Now compare that to a 300 Blackout with a 120 grain bullet leaving the muzzle at 2200 feet per second. At 50 yards that bullet is carries 1197 foot pounds of energy, more than enough to humanely stop most hogs but it’s going to be noisy, which is not what he wanted. So begins the trade off.

The problem is two fold – first is momentum, and the second is bullet performance.  Way back in the 1600s Sir Isaac Newton first explored the notion of momentum in relationship to a projectile penetrating an object. He defined the theory of momentum as “a projectile will stop in an object when it has transferred its momentum to an equal mass of the medium.”  We have come a long way from the original theory in defining and understanding momentum, but in short, with regarding to a hunting scenario, the bullet needs enough energy to penetrate the animal and reach the vitals in order to humanely put the animal down. Even though my friend wanted to use a heavier bullet, he gave up all of the advantages of that bullet by severely reducing the velocity of the round.  Even at the muzzle, the bullet carries less than 500 foot pounds of energy, less than half of what most people who study ballistic suggest for hunting hogs. In other words, most of the experts suggest shooting a bullet that carries at least 1000 foot pounds on energy upon impact to effectively and humanely stop a hog.

Then there is the bullet itself to consider. All bullets are designed to work within a certain parameters – meaning they are designed to work within a specific velocity range. Say, for example, you are using a hollow point that is designed to “open up” at a velocity between 1800 and 3000 feet per second, and you are loading that bullet to 500 feet per second. It won’t penetrate and certainly won’t open up  - in other words, no mushrooming effect. The same can be said if a bullet is loaded too fast, it may not be stable and expand to much on impact, again greatly reducing penetration. Bullet manufacturers spend a lot of time studying and testing their bullets to determine what velocities work best. Almost all hunting bullets are designated as expanding bullets, meaning they are designed so the nose of the bullet flattens out on impact and creates a much larger wound cavity. The idea is to maximize tissue damage to insure a clean, quick kill. So one can see the problem with loading bullet at a much slower velocity.

My friend was faced with a conundrum, as he wanted his rifle to be very quite – hence the suppressor - but at the same time to have a bullet that would stop a hog. What he learned, was he couldn’t have both. Yes, the suppressor will quiet – “somewhat” – a supersonic bullet but if he goes subsonic the bullet won’t have enough energy to do what it was intended to do. Of course I didn’t help matters whn I told him, “go subsonic and watch the bullets bounce off the hogs.”

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