Barrel length

[hoggy21]

Re: Barrel length

Here's as scientific as I could get it...

with my TM sopmod m4, I have a 295mm, 363mm and 509mm, 6.03 madbull inner barrel, did a grouping test at 10m for all 3 barrels, the grouping was significantly better with the 509mm... the barrels are the same type, same make, same gun, same BBs... everything is constant apart from the inner barrel length, and the longer one performed better than its shorter version. For those who say that your pistol shoots as good as your rifle, it only proves one thing, you need to get a new rifle.

So, did you use the exact same rubber with your barrels? What order did you test them in? If you have a brand new rubber then put the longer barrel on last, the rubber might of bedded in. If you used it first on an old rubber it might of deteriorated when using the others. Did you have to adjust the hop at any point during your testing, or did you use it with hop fully off? Did you have the same battery power, the same BB's, the same magazine? All factors which could effect a group size. Much the same that in real life, wet or oily ammunition effects shooting by making the round go higher, due to the excess pressure generated in the barrel, due to the gas not expanding properly.

As this website shows (http://mackila.com/airsoft/atp/) there are many factors governing airsoft rounds, environmental and physical.

And this, stolen from AirsoftForum -

After reading the pinned thread about the supposed "myth" that barrel length affects accuracy I was surprised by how little many airsofters and shooters in general know about ballistics. Hoping to find evidence from both sides of the argument I saw the thread simply degenerate into little more than a large group of people claiming that barrel length "must" affect accuracy because it just seems like it should. Starting from the beginning it appears as if no one has realised what our fellow airsofters in england have known for a while. After reading the entire thread no one seemed to be able to explain in a scientific and factual manner why barrel length was so important. They simply took it as a "fact" that had been around longer than anyone could remember and one that could not be argued against. What follows is a more in depth review of ballistics in real and air weapons.

Humans, being primarily visual creatures, obtain most of their information from what they see. As rifles and sniper weapons have usually had long barrels we seem to associate a long barreled weapon with accuracy. Why if not for accuracy do we select long weapons for long range applications? The answer is simple: a longer barrel allows the firearm to more effectively use the propellant gases therefore producing higher velocities and longer ranges. The true key to accuracy is consistency thus variables produce inaccuracy. The most prized barrels are those that have no defects and are the most consistent. Whether they are the short barrels of 22 target pistols or the long barrel of a precision sniper rifle. Many accurate guns are pistols - and many target pistols rival the accuracy of any rifle. Unfortunately things are a little bit more complicated in airsoft. An airsoft gun can be likened to an early musket. Both have smooth bore barrels. In the early days muzzle loading firearms were loaded with a slightly undersized ball this allowed for easy ramming down the barrel. When fired the ball would bounce around in the barrel due its loose fit - the same happens in airsoft. After the invention of rifles bullets were given an expanding skirt which would flare out creating a snug fit and more accuracy. In airsoft the tightbore barrel produces a similar effect. Another accuracy booster was the rifling the spinning motion of the bullet gave it stability like a football and longer range. The airsoft equivalent of this is hop up. What "justification" do people give when they use long barrel? Most say that since the barrel guides the projectile the longer the projectile is in the barrel the more it has been "guided" and the straighter it will go. The direction a projectile actually goes when it leaves the barrel is based on the direction it was going last. An object in flight will only change direction if factors influence it in flight. The main factor is gravity whish pulls the bullet down, other factors include wind. Because of this once a projectile has been in the barrel for a few inches it is already travelling in one direction a longer barrel does not make it travel "more" in that direction. Compare this to a straight line. A line with 0 deviation cannot deviate any less. The direction a projectile will go in is only affected by the last surface it came in to contact with. A barrel that is loose at the beginning and tight at the end will group the same as a barrel that was tight the whole way through. Consider a barrel with a curve at the end. No matter how long the barrel is before the curve the projectile will still curve the same amount as a shorter barrel with the same curve. This is why a good crown is the key to a good barrel. The bit of barrel a bb hits will determine whether that bb hits its target.

If you still don't believe me look at the various proffessionals that have the same idea:

This link is to an article by Ryan Cleckner


http://www.sniperschool.com/sniper-rifle-barrel-length/

Drop your g3s and m16s because the extra barrel length is only slowing you down. Next time you visit your local airsoft field try asking a friend if you can borrow his mp5. You won't regret it...

-jvarma

[blobface]

Re: Barrel length

So, did you use the exact same rubber with your barrels? What order did you test them in?

Here's an undisputed fact, I had, in my test, before me, one marui M4 sopmod, with three 6.03mm madbull black python barrels, how many idiots in this world own the same brand barrel but 3 of them in different lengths? Probably not many, but I do, and I have done that test by swapping out NOTHING BUT THE INNER BARREL, not sure which part of "everything is constant apart from the inner barrel length" did we not understand, I was also in my living room shooting to a corridor, there was no wind to speak of. In this particular experiment, in my flat, with my gun, the longer barrel performed better, they were the same Madbull barrels, while it could be silly to assume that same manufacturer produces identical quality between batches, it's as scientific as one could get it, and the result of my gun in my test, was that 509mm > 363 > 285mm (typo from before, 285, not 295), so yes, perhaps this was a human error, I re-installed the gun that accidentally favoured the longer barrel, but that's as good as I can do it.

Next time you visit your local airsoft field try asking a friend if you can borrow his mp5. You won't regret it...

No thanks, I own a 300 fps mosfet'ed lipo tm mp7.. just to give you an idea that I'm not a long inner barrel "fanboy", but I've tested my own equipment in a way that I can pass off, atleast to myself, as being scientific, and I play depending on my understanding of my own equipment, and it seems that my gun with a longer inner barrel happens to perform better due to position of the planet alignment or whatever other cosmic reasons, so I'd stick with that for games where longer range shots are required without spray & pray, this might not apply to your stuff though, since your gun isn't my gun.

[hoggy21]

Re: Barrel length

No thanks, I own a 300 fps mosfet'ed lipo tm mp7..

Blatently missed the part of my post which i typed, and which was typed by somebody else on a website i pulled it from. I would of thought that the '-jvarma' bit at the end would of given that away, considering its not my name. Please re-read and come back once you can decipher which parts i wrote, and which i pulled from the website. I did actually mention at one point 'And this, stolen from AirsoftForum.'

Anyway, onwards and upwards with this dull and repetative thread.

I am willing to accept that barrel length may effect accuracy and range, if everybody else will admit that other parts are more than likely going to need to be changed too. Inblobface's post, he states one gun may not be the same as another. Accepted. But answer me this. IF barrel length is a direct corrolation to distance and accuracy, explain to me why a stock TM M14 can outrange a stock TM M16/AUG/M249, despite the exact same barrels being fitted. The only guns with longer barrels are the Sig 550 and PSG-1. Now, if you want to increase the accuracy, you may fit a tightbore barrel, which due to an increase in air pressure might increase FPS, but not distance. That is dependant on a combination of hop and fps, as well as air seals, cleanliness etc etc. But lets go back to my original point. A TM M16, AUG, 249 are, A LOT OF THE TIME (Note: Not ALL), outranged by the M14, despite exact same barrel lengths. Also, my old TM Sopmod with a madbull tightbore barrel could outrange my SRC with a barrel length of the same.
Could it possibly, at all, even the slightest remotest chance, be the internals?
I dont know, i cant be bothered to strip down my Masada and put on the shorter barrel, because the rubber on the end of the barrel is knackered and doesnt hold the air seal properly.
If you seriously believe that by only putting a longer barrel on your gun you are going to increase range and accuracy, feel free to crack on. But i personally think sticking a slightly shorter barrel on and spending some time and money on the internal bits and bobs might be more effective in the long run. At the end of the day, its an airsoft gun, not a real rifle. And due to this, the normal laws of firearms principles do not apply in their full form.

[Bachelarius]

Re: Barrel length

It's tricky really, I do believe your findings, blobface, but I do not agree with your conclusion. Longer barrel does not simply mean better range, mainly for the reasons that jvarma's quote describes perfectly.

That's what I meant by phase. A bb bounces around in the barrel, passing through a tonne of different trajectories before it leaves. The worst of these deviations is caused by the hop itself, inducing a tonne of these vibrations. The spin forces the bouncing not to simply move in a straight lines, but adds curves as well. So the final trajectory is completely unpredictable.

Use a flat hop (r-hop, h-hop etc.) or one of the old school LRBs to reduce these initial vibration and retry the experiment. I think you will find the same as others have, barrel length effects vary with length, but go up and down with the phase of the bb's flight path within the barrel and the exit accuracy is dependent on the bb's final trajectory.

Just my prediction however

[hoggy21]

Re: Barrel length

Using fibre optics as an example, (as its my job...), in multimode fibre when light enters the way it gets to the end is by bouncing down.
http://upload.wikimedia.org/wikipedi...fibre.svg.png/
Same principle of a BB going down a barrel. Accuracy wise, the tighter the barrel, the less lateral and longditutional (sp?) movement the BB has. So, in theory...
A 700mm long by 6.06mm wide barrel will not perform as accurately as a 350mm long 6.01mm barrel.
Like i said earlier, barrel length in real firearms is applicable. See below for an article of scientific study...


Barrel Length vs. Muzzle Velocity

It is a usually accepted fact that gun barrels of different lengths will produce different muzzle velocities with the same load. Generally, the longer the gun barrel, the higher the velocity...at least up to a point. Only a few decades ago the common length of center fire rifle barrels ranged from 26" to 30". These rifles were heavy and unwieldy to carry around in the field all day. Today, the more common lengths for sporting rifles are in the range of 22" to 24", resulting in a lighter and more portable firearm. With this change many shooters want to know just how much velocity is lost in switching to the shorter barrels or how much velocity gain can be achieved in a longer barrel.

It seems that little useful information can be gained by comparing the muzzle velocities of two different rifles, of the same caliber, but with different barrel lengths. Varying dimensions in the chamber, throat and start of the rifling affect the velocity too much for a meaningful comparison. The more obvious solution is to use a single rifle, cut the barrel off, in given increments, and carefully measure the muzzle velocity at each barrel length. Many experiments were performed using this technique on both rifle and handgun. The problem was that the variation in velocity, from shot to shot, with the same ammunition, was often larger than any effect noted by shortening the barrel in 1" or 2" increments. However, if the data were plotted graphically to smooth out the irregularities due to variations in velocity measurements then a reasonable relationship between velocity and barrel length can be shown.

Various mathematical equations were developed to relate muzzle velocity to barrel length, but one of the simplest relationships was developed by Homer S. Powley. He defined the relationship between muzzle velocity and barrel length, as one giving muzzle velocity (v) as a function of charge weight C, bullet weight B and expansion ratio (R). Here the expansion ratio is defined as the ratio of the barrel volume plus cartridge volume (total volume of the gun) to the cartridge volume. The equation relating to these factors is represented by:

v = K[C(1- R^-.25)/ (B + C/3)]^.5

Where, v is in f.p.s., C and B are in grains and K is a constant that depends on chamber pressure and other factors in the gun. The expansion ratio is dimensionless. From this equation, it can be seen that for a given gun, with a given powder charge and bullet weight, the muzzle velocity is dependent only on the expansion ratio. By cutting off the barrel the barrel volume is reduced, thereby reducing the expansion ratio. The relationship can be represented by:

F = [(1-R2^-.25)/(1-R1^-.25)]^.5

Where, F is the correction factor to correct the muzzle velocity at expansion ratio R1 to that of the reduced expansion ratio R2 (shorter barrel). For example, a rifle chambered for the .223 Rem. cartridge, has a 24" barrel, and fires a 50 gr. bullet at 3,080 f.p.s. when loaded with 25.1 gr. of IMR 3031 powder. The expansion ratio is 8.5. What is the muzzle velocity if the barrel is shortened to 22"? The new expansion ratio is 7.8. Plugging these values in the equation we get:

F = [(1-7.8^-.25)/(1-8.5^-.25)]^.5
= 0.9846
v = 0.9846 X 3,080
= 3,032 f.p.s.

The new velocity for the 22" barrel is 3,032 f.p.s. The velocity loss for removal of two inches of barrel is 48 f.p.s. (3,080 - 3,032).

Note that the greater velocity increase, per inch of barrel length, generally occurs in the shortest barrel length. As the barrel is lengthened the velocity increase, per inch of barrel length, decreases. For instance, the .223 Remington shows a 46 f.p.s. velocity increase by lengthening the barrel from 20" to 22" This drops to 38 f.p.s. when the barrel is increased from 26" to 28". Some of the magnum calibers show more variation in velocity from barrel segment to barrel segment, but the velocity change, per segment, is generally less as the barrel is lengthened.

The powder charges and powder types shown in the table are for illustration purposes only and are not to be used as load data. For details on loading for a particular cartridge the reader should consult a good loading manual or internal ballistics software program. The software program offered at this web site will quickly calculate muzzle velocity for any barrel length from 18" to 50".


Watch our web site for the next topic of interest. Until then, shoot safely and know where your bullets are going.


Sincerely,
The Ballistician


Now, you may ask why this all wouldnt apply for an airsoft rifle. The main reason is rifling. When a bullet is fired, the skirt along the bottom of the round splays out, making it fit into the barrel. The rifling causes the bullet to exit the barrel in a spinning motion. This is known as the coriolis effect.
A round being fired does not actually travel in a straight line. I currently do not have the right Pam in front of me, but there is a Pam for the effects of firearms. Basically, when a round is fired, it is fired at a trajectory higher than 0 degrees (where 0 degrees is parallel to the ground.) The sight system of a rifle is at 0 degrees, whilst the rifle is slightly higher. This causes an arc in the round being fired. The round travels up, hitting its ceiling, then starts to come back down until it hits the ground or its target. This is why when zeroing an SA80, the CZP is 90mm above the bottom centre of the white patch. The round is still travelling up. The minimum sight setting for an SUSAT is 300m, so at a target 300m away the round will strike at the CZP. At 100m it is above.
In an airsoft rifle, the round is subject to Bernoulli's principle. This is that higher air pressure goes under the BB whilst low pressure goes to the top, due to the spin in the BB. Also known as the Magnus effect. When a body (such as a sphere or circular cylinder) is spinning in a viscous fluid, it creates a boundary layer around itself, and the boundary layer induces a more widespread circular motion of the fluid. If the body is moving through the fluid with a velocity V, the velocity of the thin layer of fluid close to the body is a little greater than V on the forward-moving side and a little less than V on the backward-moving side. This is because the induced velocity due to the boundary layer surrounding the spinning body is added to V on the forward-moving side, and subtracted from V on the backward-moving side. One explanation of the Magnus effect is since there is more (forward) acceleration of air on the forward-moving side than the backward-moving side, there is more pressure on the forward-moving side, resulting in a perpendicular component of force from the air towards the backward-moving side. This layer of spinning air, however, is very thin, and it is more likely that most of the Magnus effect is due to the earlier detachment of the air flow on the forward-moving side, which results in a diversion of the flow (acceleration of air) with a perpendicular component towards the forward-moving side, coexisting with an opposing aerodynamic force with a perpendicular component towards the backward-moving side.
Changing the length of a barrel will not effect the range, but changing the hop will. Using the magnus theory, a barrel which is 100mm long can achieve the same range as one of 500mm, if you can create the same magnus effect in both barrels, using a combination of hop, pressure and airflow.

[C'tan]

Re: Barrel length

Ive been told by the guys at Zero one that the barrel length make no difference in accuracy or dispense. It does work with a proper fire arm.

[Brodhurst]

Re: Barrel length

Once the bb leaves the barrel we hope it travels on a straight and true route to target. specially if we have a good air seal and tight bore barrel.

Ask yourself this question? Can an object travel straighter?

The answer is no. It either travels straight or not. So if a bb leaves the gun straight (no matter what barrel length) it will remain that way until some element puts it of course, in airsoft mainly gravity and wind. Barrel length is only important in real firearms.

Cheers

Brodhurst

[Skolob]

Re: Barrel length

I think ovet at that mevhanics forum they did it o death and concluded that 455 mm is about as optimal as you can get with a 6.04 barrel ( systema & tanio kobe also go for 6.04). Is something like... after 455 the rond is generally stabalised and you increase the probability of the bb hittng the barrel side and imparting a in that is off vertical (i.e. putting i off axis slightly).
Of course it only takes a small lean of vertical when you fire to get a smilar effect ( foun this with my old maruzen l96), you would probably get a better effect if you replaced you sight with a spirit level

[joe123]

Re: Barrel length

Don't know if anyone has mentioned this, (I couldn't be bothered to read the same thing over again).. Accuracy is also depended on how consistent your FPS is. I do however agree that a longer barrel will increase range, but only slightly.