Why is the barrel size important for the muzzle velocity and the range?
In: Engineering
A longer barrel gives the propellent more time to accelerate the bullet.
All else equal, a longer barreled weapon (within reason) will have a greater muzzle velocity – which then translates to a greater effective range.
The trade-off is that a longer weapon is heavier, slower to aim, and may have more severe recoil since it is absorbing more reaction force.
When a bullet is fired, the powder inside ignites and creates an explosion. The bullet is forced out of the barrel because that’s the only direction the force can be pushed, since all around the bullet in other directions is the gun barrel. The shape, texture, and length of the barrel affect the movement of the bullet. (a barrel that’s too wide means the bullet inside might rattle around losing its energy rather than travel in a nice straight path out. Rifling (spiral grooves cut inside the barrel) help give the bullet spin like a football to stabilize its flight. The length of the barrel translates into more time for the propellant force to do the work of pushing the bullet forward (before escaping out the end of the barrel and dissipating into the air). As such, longer barrels typically result in higher muzzle velocity, to a point. TOO long of a barrel, and the expanding gasses lose pressure, but the barrel itself introduces friction and you’d lose exit velocity, so you have to strike a balance.
The longer the barrel, the more propellant force is applied to the projectile.
Assume a very short barrel. The bullet leaves the barrel almost soon as it fires, and the propellant force dissipates rapidly all over the place.
Now imagine a rifle barrel. The propellant force is contained along the length of the barrel and acts all the way along, pushing the bullet faster and faster until it leaves the muzzle.
By size do you mean caliber (diameter) or the length of the barrel.
For the caliber it doesn’t directly matter. A bigger caliber mean a large round, but you can have a large caliber with a small case like a pistol 9mm. The small case pack a small quantity of propellant so the bullet won’t travel fast or far. On top of that the 9mm bulllet is large in caliber, but small in lenght so it’s not particularly heavy compare to smaller caliber bullet that are longer and have more mass.
But you probably mean the lenght of the barrel when you talk about size. The reason a longer barrel increase velocity and range is because the gas from the explosion have more time to push the bullet through the barrel, once the bullet leave the barrel the pressure equilibrate with the atmosphere and no longer transfer it’s energy to the bullet. It work up to a certain point at which the gas no longer have enough pressure to compensate for the friction in the barrel, so if you barrel is too long it might start to decrease the velocity and range of your bullet, but you need a really long barrel for that to happen.
A very common misconception is that a longer barrel also increase accuracy or precision and that is just not the case, it simply increase the velocity and range.
Barrel length is important. While the bullet is in the barrel, the gunpowder explosion is imparting force on the bullet. The force causes the bullet to go faster and faster. The bullet is actually accelerating the entire time it is in the barrel. As soon as it leaves the barrel there is no more pressure behind it so it stops accelerating and starts slowing down instead due to air resistance. Longer barrel means more time accelerating which means a higher velocity when it exits.
The range is increased because, as I mentioned before, the bullet will start to slow down due to air resistance. The higher the initial velocity the longer it takes to slow down and therefore can travel further.
If we want to get a little more complicated, in reality, gravity acts on the bullet as well and will pull it down long before it actually slows to a stop from air resistance. This gives bullets a rounded trajectory. Two bullets of the same weight will always fall at the same speed, but the faster one will travel further before it hits the ground. This makes it easier to hit further targets since you don’t have to adjust your aim up as much.
The simple answer is that the bullet is accelerating while it’s in the barrel, and if it can accelerate longer it will be going faster.
Once it’s out of the barrel the expanding gases from gunpowder ignition are no longer compressed by the bullet/barrel, so the acceleration ends and top speed is hit.
The longer the barrel, the faster the muzzle velocity.
The reason muzzle velocity is useful is because it’s the fastest point in the bullet’s flight.
When you fire a round, the propellant is ignited and it rapidly reacts in the chamber to form hot gasses. As more gas forms, the pressure increases since there’s not much room for it to escape.
This pressure exerts a force on the bullet, pushing it along the barrel. As long as the gas cannot escape any other way, it continues to push on the bullet.
The more time and distance that the bullet is being pushed, the higher its velocity will increase.
Once the bullet exits the muzzle, the gas is free to expand in all directions. It’s now done pushing on the bullet, and the only forces on the bullet are friction, so it starts to slow down. This makes muzzle velocity the highest velocity in a bullet’s flight.
If you’re familiar with physics and energy, you can recall the equations of kinetic energy and work.
Ek = (1/2)*m*v^2
The final velocity is related to the amount of energy given to the bullet. The bullet gains energy from the work done on it by the force of the gas pushing on it.
W = F x d (cross product)
In this case F and d are co-linear so
W = F*d
F is highest immediately after the ignition and drops slightly as the gas expands through the volume of the barrel and decreases in pressure, but the pressure is still very high until the end of the barrel, so F is positive the entire length of the barrel.
d is the distance that the force is applied over, or in this case the length of the barrel.
Since W is proportional to d, a longer barrel corresponds to higher kinetic energy in the bullet and therefor higher velocity.
The only way that a longer barrel wouldn’t increase muzzle velocity is if the force exerted by the gas got lower than the friction and drag forces before the bullet traveled the full length of the barrel.
If you imagined a perfect long chamber and barrel where gas could not escape except through the muzzle, then as the bullet moved along the barrel the volume behind the bullet increases and the pressure would decrease. If the barrel is long enough, then eventually the volume would be so large that the pressure fell below the external pressure and actually started “pulling” back on the bullet. This would reverse the force vector and cause a longer barrel to be detrimental.
I’m not perfectly familiar with gun design, but I believe gas can escape through other gaps or vents in the chamber as well. That means the pressure will decreases more quickly and stop pushing on the bullet sooner. I’m sure this is taken into account when designing a firearm and its ammunition so as not to be detrimental to its performance.
Lastly, rifling is a useful design in the barrel. It causes the bullet to rotate in the barrel so that it will have an axial rotation in flight. In a rifled barrel, the longer it is more time and length it’ll have to start a rotation. If it’s rotating in the air, it helps to reduce drag by “spinning” the air away from it and increase accuracy by helping to balance the drag forces on each side of it. You can think of it like a football (American). If you throw a football and don’t spin it just right it wobbles all over the place, and might even turn end over end.
If a bullet wobbles at all, it drastically increases its drag and reduces accuracy and range.
Latest Answers