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Bite The Bullet

Power, Range & Accuracy (2011-04-08)

As prized as range and accuracy are in Airsoft they also happen to be the very antithesis of our beloved technology. The very concept of an Airsoft weapon is that it is a softer version of an air rifle; using lower power to project a lighter pellet at lower velocity to achieve less kinetic energy.

To squeeze the best performance out of your Airsoft shooting you really do have to have at least a basic understanding of the science involved with the technology you are using.

The nature of an air pressure propelled projectile launch system is that the better the projectile is at catching air pressure and turning it into movement energy then the more efficient and effective it will be in turning that air pressure from the gun in to projectile travel energy.
Unfortunately, it is those very same characteristics that means when your projectile hits a static volume of air then those same properties also make that projectile very easily slowed and halted by that air.

When an object falls, its descent is achieved with the force of gravity. Interestingly enough, if you hold a bullet in one hand then hold a gun in the other at the same height from the ground, if you shoot that gun in level with the ground at the same time you drop the bullet from the other hand then both bullets hit the ground at the same time. One falls strait down and whilst the other may fly out a good 500m or more, it will still hit the ground as the same time.

When you shoot a BB, more power means more FPS. With a higher FPS the pellet travels faster which means it gets to travel further in the same amount of time, if it has X seconds before it hits the ground then it has X seconds to travel as far as its FPS will allow. So in theory, a higher FPS gun should be longer ranged right?

Not quite.

When you step up the FPS you are also increasing the air resistance factor on the BB. The faster the BB travels through the air, the faster the air is hitting the BB and so it slows down faster. The faster a BB travels, the more resistance it encounters. FPS does increase your range but really not by that much as most of the gain you would get is offset by air resistance.

Everything that makes a BB good for firing out of an Airsoft weapons makes it equally as bad at penetrating though air. Equally, while it is good at harnessing the gust of air from your gun it is just as enthusiastic about harnessing cross winds to throw itself violently off target. IN much the same way as Air resistance in static air, cross winds mean that your BB is much to keen to grab that random gust of wind and flit off in the wrong direction.

Gravity is a constant downward force so the effect that it has on a BB in flight is a constant factor. The hop-up is a backspin to create aerodynamic lift to counter act the gravitational drop effect.

In terms of engineering, the back spin is created by applying some kind of friction or torque on the BB as it flies out of the weapon. The hop-up unit uses a piece of rubber (bucking) to graze the top part of the BB such as to slow the top but allow the bottom to continue. The result is a BB that spins backwards as it flies, as such, creating aerodynamic lift.

What this means is that you BB starts with X amount of FPS then when it hits the hop-up unit the bucking slows the BB down to X minus Y FPS. By slowing it down, it steals away that energy to add spin to the BB. Hop-up is not just good for range, its incredible. It takes all that bloated characteristic of BB aerodynamics and uses it to turn the BB into a little wing increasing its range significantly.

As discussed, FPS helps with range but not by a lot but hop-up on the other hand is great. If you have a small amount of energy to work with, it is far more effective to spend it on the hop-up up then the FPS in order to achieve distance. As such, for an Airsoft weapon, the FPS could be anywhere in a window of 300 to 500 fps but its terminal range is not that much different but even a minor tweak in hop-up energy and that pellet can now outrange everything else on the field.

FPS will mean your pellet gets to your target sooner which means your target has less of a chance to move out of the way. The faster your target is moving, the more you have to lead the target as you aim in order to account for travel time of the projectile. The higher the FPS, the less lead you need to add. A 300 fps rifle with an incredible hop-up can most certainly hold well out to 30 or 40m but it will take so long to get there that it is hard enough to hit a slow moving target but hitting a running one can be close to impossible.

Furthermore, BBs slow down quite a bit in flight. If you are shooting at great range, by the time the BB gets there it could be of such low energy that it can strike a vest or jacket with almost no feeling at all. Our 300 fps rifle with an incredible hop-up can most certainly hold well out to 30 or 40m but by the time it does hit the target it might be traveling at less than 150 FPS making it quite likely that your target might not even feel it.

A BB travels down an inner barrel on a cushion of air so it does not touch the sides. This slight give also means the BB can move side to side inside the barrel, not much, but just enough to allow those BBs to come out of your barrel in a cone pattern instead of a line. A tighter barrel means less space which means less wobble which means a tighter cone. A longer barrel means more time for the BB to stabilize its wobble which again means a tighter cone.

It is important to consider the cone because your well tuned rifle might well be able to land BBs a good 50 or 60m away but if they are landing 10 or 20m apart then that accuracy is so low you cannot count on it to hit anything really. If you have a fully automatic assault weapon then you can create a beaten zone of area denial to keep heads down and hold opposing forces back.

If you have a bolt action or semi-auto weapon, if your landing pellets any more then 3m apart at range then you will have to empty whole magazines before you can expect to hit a human size target at that range.

The point being made here is that the length of your invisible cone is your maximum range but the weapons maximum effective range is the greatest distance along that cone before it is wider than the target you are shooting at. For a full auto weapon, a spread of 5m still puts enough pellets in your central 0.5m to be a threat but a slower firing weapon really can only afford to only land shots inside that 0.5m wide human zone.

So to sum up; range comes from the hop-up, FPS gives you flight time and distance to felt hits and barrel tightness and length gives you accuracy. Barrel length and FPS does not give you more range. Range is good but unless your landing 50cm groupings or tighter, that range at and beyond that point is pot shots.

A bolt action weapon shoots so slow that it absolutely must be shooting at targets up to the 50cm diameter cone section to be effective. A semi-auto has enough firepower to stretch its statistical likelihood of hits out to maybe a 2 or 3m diameter section of cone, beyond that its pot shots. A full auto weapon with high fire rate can deliver human kills out to 5m diameter cone section but if the intention is suppressive fire then you actually want a cone diameter section out to 10m across to create a deliberately poor accuracy so that the pellets are 5 or 10m apart but still have enough FPS to feel thus you create a kill zone area rather then a small window.

Airsoft is about having fun but the technology is about science. Play to have fun but if you want to be effective it pays to have a good sit down and think about things. Plan out your intentions, do your research and talk it over with experienced players and Airsoft engineers. Just because real guns work that way does not mean Airsoft will. Just because you think things work a certain way, does not mean they do.

- Arclight