For all their relative simplicity. Seemingly little is know about the exact physics of airsoft guns, especially when it comes to hopups and exactly how the BB interacts with the barrel given its backspin.
I have heard all kinds of crazy things, things like polishing barrels with car wax or how shorter barrels are actually better.
The second one I am particularly curious about. I keep dismissing it but it keeps coming up. So exactly how much truth is there in this claim?
I suppose that it does make sense to an extent in the sense that a shorter barrel minimized the number of bounces that the BB makes inside the barrel. Optimally a super tight, super short barrel would be best since it has almost no bouncing.
But that just works against all the common logic out there...
What do you all think about this?
A shorter barrel means less friction with the pellet. Less friction means less resistance applied to it, so less energy lost on the way out to the barrel. Less energy lost, means more kinetic energy kept in the pellet.
It's law of "energy within a closed system is never lost". Well a gun is not really a closed system and there are many outside factors (temperature, lubricant in the barrel, hopup, actual mechbox, weight of the bb, etc...). But still, less friction means more kinetic energy. More kinetic energy would theoretically mean a longer distance reached and/or a higher speed as well.
This needs to be said so you can understand the whole thing.
Now inside the barrel, the micro bounces you mention, are indeed happening, and a barrel's job is too make sure that the kinetic energy transferred to the pellet, is actually guided into one accurate direction. In the early stages the pellet has no kinetic energy, and when the mechbox is activated, a lot of compressed air rushes through the muzzle, pushing the pellet, and initiating its kinetic energy. Since it goes "wild", the pellet do a lot of micro bounces, and if the barrel is too short, the pellet won't have enough barrel to minimize the micro bounces and the pellet will just go wild out of the barrel, being rather inaccurate.
The longer the barrel is, the more it is able to minimize micro bounces by guiding its trajectory, and eventually reducing the bounces to a minimum making the gun as accurate as possible.
Sniper rifles have a long barrel for a reason... not just for the look, but for its accuracy
Also, to counter the friction of the barrel, and have enough mass/energy to reach far targets, the bullet needs to be bigger and with more propellant, simple physics.
Hope it helps ^_^
My take on the whole thing is that it’s really all about the back spin of the BB. In real firearms the bullet clearance of the barrel it's self and the barreling is about 0.008 to 0.014" on production rifles and 0.002 and creates the spin that allows the accuracy of the bullet, the pressures and effects of the vortices actually warps the bullet and leaves markings on the surface of the bullet and thus creating the spin of the bullet that has led to greater accuracies over the standard tube style barrel.
In Airsoft the BB is free floating in the barrel the pressures forced on the BB as it travels down the neck of barrel don't really have as such a significant effect on the physics of the flight of the bb but act more in a way guiding it in the right direction.
Having put a lot of hours and resources into the theory that back spin that the hop unit places on BB has more to do with accuracy in flight, I have come to the conclusion that this is in fact the case. Using Madbull Fish bone nubs and custom made swing arms I have created a hop unit that puts (as close as possible) equal amounts of pressure across half of the BB as it pass through the hop unit. This prevents the BB from having an off sided spin that can create deviation either left or right and also creates a larger surface exposed to the friction as it passes through the bucking, thus increasing back spin and reducing inconsistencies found in stock hopunits.
I have used this technique and method on a lot of my custom built rifles and the one replica that finalized my conclusion was the MadBull Noveske Talon CQB rifle I built. The weapon has a barrel exactly the same length as the Tokyo Marui G17, yet it is able to reach out accurately to 40-50 meters hitting a human shaped target with a 6.03mm barrel. I then used the same techniques in the MP5A3 with a stock 6.08mm barrel and the results were the same.
So in my opinion If you looking to increase accuracy, then I suggest you increase the back spin. Oh and as some of you have found…..even with lower FPS and higher back spin this design is still able to hit the 50m mark.
FarEast, tell me if I'm wrong, but you're mentioning accuracy like it's the actual range that matters. I for my part took apart the differences. Greater range should be achieved with shorter barrels, (I don't mention any spin or hopup because my knowledge of it is really limited at this point), but better "accuracy", should be reached with longer barrel.
Now, this is all theoretical, and honestly, BBs are so light and really not shaped for long distances, the slightest wind will screw up any accuracy test in real life game, and the difference between longer and shorter barrel made void, accuracy wise.
Kinetic energy wise, shorter barrel should still be better though. Again, less friction.
I guess we're all speaking from experience, so I'll give my own observations on the matter...
One thing I know between long and short barrels are, gas laws applies (from physics/chemistry). To produce the same muzzle velocity, a shorter barrel needs more pressure and less volume, a longer barrel needs more volume and less pressure.
With regards to accuracy and stability, an effective hop up is indeed a factor. But so is barrel length. The longer the BB is in a barrel, the longer it is protected from the effects of the environment. But then (correct me if I'm wrong), hop up spin will only work once it's outside the barrel.
I'd like to see how this discussion goes...
Mmm, I didn't consider the factor of gas expansion and volume moved. I just thought about the initial "push" given by the mechbox's muzzle to the BB.
Also, about the effects of the environment being delayed on the BB on a longer barrel, I do believe it's true to some extend, but not sure if something like 10 or even 20cm really make any noticeable difference. If there is wind after all, the 20cm won't change the fact that the BB will go off target anyway.
No ?
Anyway, I need more experience and tests to understand how the whole spin and hopup actually change trajectories and distances, I have no idea how it does that yet ^^
I actually have the Madbull Noveske Talon that Far East was talking about lol!
I got it from Anarchy.
I wonder why rifling an airsoft gun does not work... Moreover, why are BBs spherical? I mean if you use a spring loaded magazine, a cylindrical pellet would be practical, especially if you want to rifle it rather than put backspin on it.
I guess if you rifle a BB, you have to also put enormous force behind it for the pellet to engage the rifling. This would mean that the pellet would come out at dangerous velocities...
I'm curious about rifling too, as I just watched the latest episode of Mythbusters about curving bullets in Wanted.
In their last test they machined a gun barrel to remove the rifling, and that made the bullets unstable. And I wondered, would it actually matter in an airsoft barrel?
Tanio Koba has rifled barrels, and I actually have one on my HiCapa, but there doesn't seem to be any obvious effect. Maybe if it were longer? But I recall reading in other forums that the rifled barrels are more inconsistent at velocities above 300 ft/s.
Rifled barrels make a difference for projectiles who would actually benefit from it.
A BB being a round plastic ball, should not benefit from it much, since it doesn't have a front and a back, it's round.
As I saw the Mythbusters show too yesterday (funny seeing Adam in the Hornet haha
), I was exactly thinking that, since we don't have any rifling, our BBs must be "going nuts with spinning", but then I remember we actually have the hopup system which give a direction to the spinning.
For real bullets, spinning wildly in mid air doesn't really improve their speed nor penetration, especially if they hit the target on their side
If we were to change the projectile used in Airsoft, for something looking more like a real projectile, then rifling would definitely be necessary I think.
Any expert to agree or disagree with what I said ?
By the way, the instructions that come with the Tanio Koba rifled barrels says that if you set too much hop, the BBs will fly upwards and right. So does it mean that using Tanio Koba barrels will give BBs a diagonal spin?
I guess it means that it gives the BBs a left to right spin (like rifled barrels do), which combined with the bottom to up spin of the hopup will result in a nice diagonal and a lot of energy wasted
TK barrels don't rifle the same way that real steel guns do. The rifling in TK barrels is theoretically supposed to provide this "cushion" of air around the BB so that the BB does not contact the barrel. I have heard TONS of debate over their effectiveness. The only conclusive point seems to be that if the BB is traveling faster than 96 m/s then it doesn't work.