How Fast Does A 556 Bullet Travel In Mph – When I was younger, single and didn’t have as many responsibilities in life, I was into cars and drag racing. There’s something about the feeling of going fast that never gets old, no matter what. When it came to the engine, they said:
It almost always comes from guys who drive their big eights looking at my supercharged Fire Four. Regardless of what the technology was underneath, there was no getting around the benefits of really big engines.
How Fast Does A 556 Bullet Travel In Mph
This is true in many different areas of ballistics and rifle engineering, and I’ll get to that in time. For now, I want to focus on the relationship between rifle barrel length and velocity.
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You saw some math in my discussion of barrel spin rate. But there’s really more to it than that.
In this article, we focus on the physical forces that propel a projectile through a rifle bore.
First, note that the cartridge has a fuel source enclosed in a brass case. The projectile sits on top of the fuel source and seals one end of the box. At the other end you will find the sealed bottom of the box and a small hole for the primer.
In this configuration, each cartridge is independent. When you think about it, you have all the ingredients for a small rocket engine. By sealing the cartridge in the chamber, the entire bore of the rifle becomes the rocket nozzle. As the fuel burns and emits high-pressure gas, it spreads in all directions.
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The side walls of the box press against the inside of the chamber, which is made of stronger metal. The walls of the chamber will not “pass” the expanding gas. The bottom of the cartridge presses against the face of the bolt, which is mechanically coupled to the rifle. All the energy expended here is transferred to the rifling and the material, where it finally has an impact.
When considering the combination of the chamber walls, the face of the bolt enclosed in the bolt housing, and the trigger, can only expand in the direction that the expanding gases can expand in the bore and muzzle.
The bullet is between the self-igniting powder and the expanding gases of the muzzle. That increased pressure has to go somewhere, and it’s easiest to move the bullet to that point.
The pressure builds up until it overcomes the friction between the bullet and the bore. Again, the ability to sustain pressure here is not infinite. The reloading chamber and face have to withstand more pressure than just a bullet in the bore.
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We’re talking quite a bit of pressure in the neighborhood of 51,000 PSI for a .223 cartridge. This pressure accelerates the bullet down the bore until it exits the muzzle and exposes the bore to the open air. At this point, the gas is exhausted and the pressure in the pore returns to equilibrium with the outside world.
This simple example shows what it looks like when you strike the primer, ignite the powder, and watch the expanding gases push the bullet into the bore.
Physics being what it is, the weight of the bullet coming out of the gun combined with the force of the expanding gases coming out of the mouth like a rocket nozzle is what you feel recoiling.
Continue increasing the speed. Therefore, when larger holes need to be traversed, there is a greater possibility of increased velocity.
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The short answer is yes, there can be too much of a “good thing”. Remember that there is a lot of friction between the bullet and the inner walls of the barrel. A seal between the bullet and the bore is essential, otherwise gases expanding behind the bullet will pass through.
All that friction is fine as long as there is enough pressure behind the bullet to overcome it.
The problem arises when there is limited amount of fuel in the cartridge. If we had an infinitely long barrel, there would be an equilibrium point. By this I mean that the bullet will have gone deep enough in the bore that the back pressure will begin to decrease. It may not return to ambient external pressure, but it won’t be high enough to keep the bullet moving.
This basically happens with a squib charge. Not enough pressure was created to push the bullet out of the bore.
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All this means is that you can increase the length of the barrel and still squeeze more velocity out of the shot, but at some point the bullet will start to slow down again until you burn with a larger cartridge case. Do not increase available fuel. .
The bottom line I want to take away from you is that there is a lot of engineering that goes into finding the optimum bore size for a given combination of powder, caliber and bullet weight.
All these calculations take place during the initial development of the weapon system. This is one reason why a new gun usually comes with a new cartridge.
If you look back at the history of the AR-15, you’ll see that we didn’t just fire the 55gr .22 bullet out of a 20-inch barrel. The design was based on decades of research and experimentation, and the final specification was a 55 GR projectile fired at 3,300 feet per second and penetrating a steel hull at 500 yards.
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In this graph, which tracks the velocity of a 62gr M855 bullet fired from different barrel lengths, you notice that going beyond a 20-inch barrel is no longer worth it. The system is optimized here.
A big mistake is that a longer barrel makes your rifle more accurate. it’s wrong. Barrel length does not affect the mechanical accuracy of your rifle.
What actually happens is that the bullet’s ballistic curve flattens as velocity increases. In other words, you need less eye adjustment or holding to take the shot.
Because of this, you find it easier to hit a target when you have more speed. I have two ways to show you this. The first is to use the concept of zero vacuum.
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The first is a 20-inch M193 gun firing at 3300 FPS, the second is a 16-inch gun at 3100 FPS, and the third is a 12.5-inch gun at 2900 FPS. These represent my three favorite barrel lengths for the AR-15.
I used 8″ as the “vital zone” for the blank range which represents the -0 zone of the IDPA target. Yes, I know…IDPA is for pistol rounds, come with me because I love this cute round number.
Note that as the barrel length decreases, the point-to-blind distance increases inward to keep the shot velocity within +/- four inches.
If we’re being honest, the difference between a maximum zero range of 296 yards and 333 yards isn’t that great. However, this is an ideal situation.
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These are not normal zero distances. I don’t know of many ranges that allow me to accurately zero the sights at 232 yards.
For this practice I use the same barrel lengths of 20″ 16″ and 12.5″ shooting 55gr M193. I also aim at 25, 50, 100, 200 and 300 yards for each.
It’s not that obvious because these charts only go out to 500 yards, but as the distance increases, the distance between each curve becomes more apparent.
In comparison, when zeroed at 100 yards, a bullet from a 12.5-inch gun lands about a foot and a half further than a bullet from a 20-inch gun at 500 yards.
Caliber Hi Res Stock Photography And Images
Now, whether you would actually use a 12.5 inch barrel at 500 yards is a very different matter and beyond what we are talking about here. At this point, please note that I have not considered built energy in any of these charts or graphs. Punching a hole in a piece of paper is one thing, but the reality is that the impact causes significant damage.
I took each chart from zero distance and showed where the IDPA would hit the target. For each shot, we assume a focal point of intent, which I’ve highlighted in red.
This IDPA silhouette shows the impact of 20″ rifle rounds at 300 yards
In this example of a 25 yard zero, both the 20″ and 16″ hit the ground at 400 yards, though just barely. 12.5″ is not even close. Also note the effects at 300 yards. As the velocity decreases, even slightly, it continues to move toward the target.
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Next, let’s look at the 50 and 100 yard targets. What impressed me on the 100-yard zero target was the performance of the 20- and 16-inch barrels.
Now look at the 200 yard targets. All show nice tight small groups from zero to 200 yards in the center of mass. This is why the 200-yard zero is so popular with practical and military shooters.
Overall, this 200 yard zero is great.
