Airsoft Precision Barrels

Aggressor wrote:works at AirSoftAtlanta

My major in college is aerospace engineering, and I've taken more mathematics and physics courses than I'd like too. So here is a brief analysis to verify that a longer barrel inherently creates a more accurate gun than a shorter one. Even though everyone knows this for real-steel, and virtually anything that launches a projectile.

Projectile: an object that moves in two dimensions under the influence of only the gravitational force.
(Physics: For Scientists & Engineers, by Randall D. Knight)

Vfx = Vix * Cos(Theta)
Vfy = Viy * Sin(Theta)

Where Vfx and Vix, are final and initial velocities in the horizontal direction. And where Vfy and Vix are final and intial velocities in the vertical direction.

If the projectile is first propelled through a barrel, then the vertical velocity is virtually zero. I say virtually because there is a small deviation within the barrel and bb. If there is no deviation between the two surfaces then the friction is too high for impending motion, where a force applied is larger than the static friction within the barrel. Once the projectile is in motion, there are two frictional forces acting on the projectile.

1. Friction due to barrel: There is kinetic friction on the bb as it moves through the barrel. Which is determined by the equation F = uX. Where u is the coefficent of friction for the barrel and bb, and X is the distance of the barrel.

2. Friction due to air: Any object that moves through air has some characteristic of air resistance, this is complicated, as it is dependent on the surface area of the object, mass, or density, and also velocity. The general equation is D = -Bv, where B is the damping constant, as long narrow objects have lesser damping constant than that of flat objects, v is the velocity, and D is the drag force.

In general, if we treat the bb as a particle, and apply particle physics, igonoring rigid body physics, and if we ignore friction, then the only force acting on the object is gravity, along with the disapating force of the piston that thrusts the bb out of the barrel.

The barrel will contain the projectile, and keep it's motion within a horizontal direction, thus only a horizontal velocity.

Looking back at the equation, since the sine of zero is zero, and the cosine of zero is one with respect to the angle between the barrel and bb which is parrallel, which is zero. Thus even if there was a intial vertical velocity, sine of zero is zero, meaning the resulting final vertical velocity is also zero. This is due to the barrel impeding the motion of the bb in a vertical direction. Meanwhile, the horizontal velocity is at a maximum, as cosine of zero is 1, meaning that initial horizontal velocity is equal to the final horizontal velocity.

The equation for this velocity is shown by the energy equation.

KE = (1/2)*m*V*V

Unforunately I am not able to write velocity squared so I improvised and just multipled it twice by V, which is the initial velocity, and also muzzle velocity. Where m, is the mass of the bb, make sure that is in kilograms, and KE is the energy. So if you know the joule of your spring within your gun, solve backwards, then you get your muzzle velocity.

However, once the bb leaves the barrel, then the barrel no longer impedes movement in the vertical direction, and the bb due to Bernoulli's principle of fluid dynamics the projectile now will have lift, causing it to rise to a certain degree, depending on velocity. Hop up places a spin on the projectile to help maximize the idea of lower and higher air pressures created by the surface of area of the bb to maximize the distance the bb travels.

Because the bb now can move in a vertical direction, then it is no longer moving only in a horizontal direction alone.

Thus, a longer barrel helps keeps the projectile moving in a horiztonal direction. There is probably some time function equation, that relates how long a projectile must stay within a barrel to dispate the vertical initial velocity/ force on the object created by the piston. But, the longer the barrel, the more time it it allows for the dispation of that vertical velocity, because real world wise, there is friction, and air resistance, along with that small deviation between the barrel and bb that causes that vertical intial velocity. Therefore the longer barrel equals better accuracy, with airsoft or real-steel, whereas the shorter barrel equates to lesser accuracy.

Hopes that helps to settle the myth, but you don't have to take physics or math to understand this, just look at real-steel, you don't see short and stubby sniper rifles.

And there is a whole other set of equations that help snipers determine distance, and drop of there round, all formulated by the weapon they are using, the distance they want to place the shot, and the round they are using. But I won't go in great detail with that because it is finally Christmas over here and I don't have time.