Barrel Length And Accuracy

ZeroSignal

I found a very interesting thread on another forum regarding barrel lengths and how they affect accuracy. According to this thread, cylinder compression has a lot to do with it too.

http://www.acmeairsoft.com/showthread.php?t=8358

The parts I find most interesting are these posts:

wrote:

LOL - and I even more rarely disagree with you, but here I must. Unlike in a real-steel rifle, where the powder continues to burn behind the bullet, constantly increasing velocity until either the bullet "uncorks" the barrel or the powder is fully combusted, AEGs get all their acceleration in the first three or four inches of barrel. The piston puts out one "puff" of air behind each bb - that bit of air does all of it's work almost instantly. Longer barrels don't matter, as the bb has gotten all of the impetus it's gonna get.

Obviously, there ARE exceptions to this general blanket statement. REALLY short barrels might not be long enough for the bb to reach full velocity before exiting, therefore "wasting" the air that escapes behind it. Also, if the cylinder port-location is mismatched for a given barrel length, you might see an increase if you lengthened the barrel (or you might see a decrease too - depends on the mismatch). Generally, though, given the proper cylinder and a barrel of anything other that very stubby proportions, that extra tube isn't doing anything.

Another exception is GBB, in which the gas continues to flow until after the blowback cycle, which doesn't even begin until the bb leaves the barrel. In that case, more power is being applied during the bb's entire length of travel. An extra inch in a GBB can make a significant difference. But the mechanism is entirely different from an AEG.

-Tuthmose

EDIT: I'd be interested to see some tests to show how long a barrel is sufficient to achieve this max velocity. I know it's only a couple of inches, but I'd be interested to know exactly how much, with say, a standard cylinder.

wrote:

the testing is already in the works

results...


longer barrel with heavier bb's improve accuracy BUT the longer cylinder stroke length decrease hop effect and reduces accuracy

short stroking a short gun can give better hop control and accuracy but the shorter barrel can lead to less stability

longer tighter barrels lead to smoother velocity increase
shorter tightbores can run better while moving
shorter open barrel can have massive power loss
longer open barrels can cause vibrations and loss of accuracy and fps

so... it just depends on the combination
IMO

As a rule it goes center/center short and long are bad in a stock barrel
the shorter or longer the barrel the better a tightbore is
short stroking produces better hop up and are better for cqb
long barrels produce that don't move create a stable platform

wrote:

mix and match cylinders, little things seemed best so far, harder springs cut shorter are more consistent, transfer more energy at the start which means you can use heavier bb's and apply more hop for a better effect, that means even running bore ups in mid length barrel and short stroking them.

then add in other factors
a barrel properly molly treated has less bounce and vibration
it also has less resistance on the hop rubber so you can use a longer barrel
h nubs get more grip on a bb with less pressure as well, so when you combine an h nub in a proper molly barrel, short stroked with a heavier spring to make up fps you actually get more consistent accuracy

All this comes out to... the heavier a bb is the shorter the barrel for better effect at the same fps (comparing a 1j .2 to a 1j .25 and up).
BUT since most people run .2g bb's the higher the fps the longer the barrel needs be to stabalize. Or in other words longer barrel for the 2 bb do make more accurate results. And if you use a .25g or heavier then it throws a wrench into all that and short barrels, short stroked with front porting cylinders, with molly barrels and h nubs rule in my tests so far.

It's why the mk23 sniper pistol (6.00 tightbore with highflows) that shot .2's at 500fps were all over the place but when we used .4's we could outshoot sniper rifles.

I'm planning a full test of all these factors at once, eventually but the total parts and setup to do this right is around $2,000+ not including my lab testing equipment for it. So it will wait till spring.

When I say run heavier bb's no one gets it, even TM's were designed for .25g bb's they include them with the replicas. And they only shoot 300 with a .2 in energy.

wrote:

IMO The reason full cylinders usually get less out of a short barrel (especially with lighter bb's) is the speed of the start of the air compression. It starts low and builds up, this means the bb leaves the hop at a lower speed and then tries to accelerate. A bore up with porting would solve some of that. (I actually was running tests o short stroked bore ups in mid length barrels with good results, only thing is the bore up parts suck)
Short stroking, higher spring power and more forward porting means the pressure is on harder faster and that transfers to more pop from the hop unit and better results from a shorter barrel (and even mid and long ones). My testing showed also that if you move the replica while shooting (like turning) a long barrel can make the bb do weird things i.e. curve.

I suggest short barrels for most, mid length for outdoor play and only a long barrel if the replica is to be shot from a stationary position. Even then a mid length barrel at the same fps can usually outshoot a long barrel.

Discuss.

Firekitten

From personal experience, i find 'quality' of barrel gives a better performance than length.

Some say 'oh i put an m16 barrel in my m4, it shoots so much further and more accurately'

what they forget to mention is they took out the stock 6.08, and put in a promy 6.03...:rolleyes: (or similar).

Cylinders hold a fixed volume, as the article says, it doesnt help with airsoft. However, at low fps, and short barrels, the accuracy and range will be improved by a longer barrel. However, there is an optimum length for the cylinder capacity, a relatively fixed entity in airsoft (if you want to maintain decent fps).

At 1j, and around 400mm is your optimum I find, 350 in england, its a little shorter, m4 length, the volume is expressed faster, and thus, barrel length to cylinder ratio is lower...

One could go into insane scientific detail, but I spent the morning lecturing classmates on why the jet stream being abnormally far south leads to flooding, and haven't the breath to continue :P

ZeroSignal

• Firekitten wrote: »

Cylinders hold a fixed volume, as the article says, it doesnt help with airsoft. However, at low fps, and short barrels, the accuracy and range will be improved by a longer barrel. However, there is an optimum length for the cylinder capacity, a relatively fixed entity in airsoft (if you want to maintain decent fps).

At 1j, and around 400mm is your optimum I find, 350 in england, its a little shorter, m4 length, the volume is expressed faster, and thus, barrel length to cylinder ratio is lower...

Thanks for the good post.

What one poster there mentioned is to shorten the piston stroke by removing teeth, therefore making the cylinder capacity "smaller". That would probably be a good way around changing the size of a cylinder.

Firekitten

No real need to be honest... Vented type for shorter than 350ish, non vented over... Im saying 'larger' than standard size, is needed to truely make use of a longer barrel. Shortening the size of the cylinder that way will force you to crank uip the spring size to compensate, stress your gears, and deffinately stress the piston forcing it to engage earlier than it wants to.... There's really no NEED to make it smaller capacity....

Phractal

Ok I actually wrote an article on this, funnily enough. I will recover it tomorrow and post it up, it was originally sent in to Take AIM but ah well may as well provide it as free information. It uses basic physics to explain why longer barrels = diminishing returns. Basically, a longer barrel WILL stabilize the BB more, PROVIDED it is a quality barrel. As FireKitten said, quality is more important than length. Basically, the barrel must first be of high quality. Then Cylinder Vol. Must match Barrel volume.

.22 Lover

Are prometheus worth the few bob? i stuck one in a classic army M15A4 SLV [long version] turned it into a dboys SPR mod 0 new hopup with standard rubber kept the old gearbox and now its weaker then my Glock 26c pistol anyone know what the problem might be?

Witcher

.22 Lover wrote: »

Are prometheus worth the few bob? i stuck one in a classic army M15A4 SLV [long version] turned it into a dboys SPR mod 0 new hopup with standard rubber kept the old gearbox and now its weaker then my Glock 26c pistol anyone know what the problem might be?

Is the hop rubber and unit on the barrel correctly, could be an air leak there. Also after spending money on a Prommy barrel it's a shame to use a standard hop with it, a Guarder one would get the most out of it.:)

.22 Lover

i got a guarder hopup rubber but destroyed it trying to get it on this is my first airsoft gun and first time upgrading so there could be an air leak

Witcher

.22 Lover wrote: »

i got a guarder hopup rubber but destroyed it trying to get it on this is my first airsoft gun and first time upgrading so there could be an air leak

Best thing to do is strip the hop up again and put it together carefully, make sure the hop rubber isnt being forced too far down the barrel by the unit going over it.

.22 Lover

how far down should it be it currently just the slightly smaller ring part that's not on the barrel and the nub is in the square hole where i think it should be anyway.

Phractal

Barrel length and effects on BB velocity: The simple truth.

I have read in Take AIM (issue 4, ICS M-16 review) that longer barrel in an AEG gives greater accuracy, and often gamers claim a longer barrel gives higher velocity. This belief is especially seen as ‘Gospel Truth’ amongst the Sniper types in Airsoft.

THIS, is a lie. A basic misconception often seen also in real steel circles, which has passed on to the airsoft scene.

I hate to talk about real steel in an airsoft article, but its very relevant in order for you to grasp the concept I am explaining, which is firmly based on physics. In a real steel firearm, barrel length in a .223 rifle is often 20 inches or so, like a M-16 rifle. This provides high velocities and excellent accuracy. The M4 carbine, with 14 inch barrel, has a lower velocity and range – or so we are told. Target rifles often have huge long barrels for accuracy, and this leads to the belief of ‘longer barrel = better’. However, the truth is that barrel length is not truly relevant. People have used .223 weapons with down to a 6” barrel with the same result as a 20” barrel. Why is this? You say. This is counterintuitive. Well, the barrel length doesn’t matter due to the powder charge. If the powder is still burning when bullet exits, velocity suffers. If the bullet is still in the barrel when powder burns out, velocity suffers as the ‘push’ is gone, and the rest of the barrel is merely friction, slowing the projectile down (different powder loads deal with this).

HOW does this translate to airsoft? You say. Well… If the piston has ‘bottomed out’ before the projectile has left the barrel, the BB is slowed by friction, and a phenomenon known as ‘suck-back’ occurs as a small vacuum can be formed. This is because the 'push' is gone. This further slows the BB, lowering velocity – and therefore accuracy. This effect is rather noticeable in the VSR-10 type rifles where often the piston bottoms out prior to the projectile exiting the barrel..

AS for accuracy, it is the last two inches of barrel that decide upon the direction the projectile takes.

If the piston has bottomed out after the BB has left the barrel, it is merely inefficient and some power is wasted. Also, the push of air following the BB can kick it off course a bit, losing more accuracy. This occurs if the barrel is too short, and if the axial alignment at the muzzle is not dead on the puff of air will CERTAINLY skew the projectile off target.

Now the thing is – one should have figured out at this stage that the optimum barrel length is evidently a goal. How do we find this? You say. Well… Look to the maths! Find the volume of the cylinder with the piston to the rear (cocked), by the simple mathematical formula (3.14*radius*radius*height) (exchange ‘height’ for ‘length’) of volume of a cylinder. Now this volume should be the volume of your barrel. By working backward from the volume, the barrel diameter being found with a vernier calipers, one can calculate the optimum barrel length.

Now your barrel could well be too bloody long for the gun. HOW on EARTH do we deal with this? Well, we have two options. One option is to ‘port’ the barrel, the other is to saw it off. There are various good, and bad, points to both of these.

Obviously, I advise doing this to a tight-bore barrel for best results!

Now to the business… First we shall examine why porting is a godawful idea.

Porting involves making a hole in the side of the barrel to let air in after the piston is bottomed out, killing the ‘suckback’ effect. HOWEVER, this has two BIG disadvantages. First, the BB is often ‘shaved’ by the port, deforming or breaking it entirely. This puts the **** to your accuracy as the BB is mangled – sometimes it even JAMS! Also, the remaining barrel length is merely friction, and therefore slowing down the BB. Porting is merely used as it means your AEG looks the same still.

Sawing off is the way to go, as it kills the suck-back, maximizing velocity and has optimum efficiency. Also the BB does not get ‘shaved’ or such. However the AEG’s aesthetics may not be the same – people don’t saw off their PSG-1 (another weapon with an over-long barrel - at least the TM one) as they sacrifice velocity and efficiency for realism and looks. If sawing off, ensure the muzzle is exactly 90* and re-crown it..

The way to fix the aesthetics is to make the gun ala ‘shortie’ with a new barrel end kit, making it look the same, merely shorter or ‘stubbier’.

Another way is to build your own barrel. This is NOT easy to do, and I only recently managed one. My barrel is entirely plastic, extremely smooth finish, and 5.99mm ID. Unfortunately it needs improvement as a fall killed it – the plastic used was too brittle. Once I get the process down you may see ‘Mr Martyns Polymer Precision Barrels’ on sale in your airsoft shop… MAYBE.

Happy playin’! Darren.

ZeroSignal

Excellent post, Darren.

So, is there anywhere I can find out more about standard cylinder capacities?

Also, how would a Tanio Koba Hop-Twist barrel affect suck-back?

Firekitten

A tk twist will have the same performance as any other barrel when suckback occurs... the tk difference is merely accuracy increasing...

ZeroSignal

Firekitten wrote: »

A tk twist will have the same performance as any other barrel when suckback occurs... the tk difference is merely accuracy increasing...

Okay, my problem is that I really like the aesthetics of the AK-74M (502mm) but would the accuracy difference really be much more noticeably better if I got an AK-105 (360mm)?

gungun

great post:D
on the tk twist barrels, would the indented rifleing very slightly increase the volume of the barrel putting off your results or would it be an insignificant difference?
after reading that im gonna take a while checking the vsr:)

Firekitten

On the aks... Firstly the 74 has a 415-495 length inner... 520 would poke out of the vent on the muzzle, or end of barrel by my reckoning. The 105 is 295 to 380, At either extreme, not really, The shorter 105 barrel would require a vented cylinder for optimum power output, whereas the 74 would require a non vented. Which would be more accurate? Depends what the barrel inner diameter is... I've not seen 'significant' difference between any ak model besides the aksu and shorter barreled 105s. The 74 's performance would be best with a non ported as 420 is roughly the length you'd want for a v3 cylinder, the standard barrel length from the tm ak47. (same as the 74 just add muzzle brake.) Longer than 420ish begins to be a tad silly unless its a longer cylinder.


On the TK twists... No, The 'inverted rifling' or channels in the barrel are full of air. As the bb passes, they are under pressure, and actively seal the barrel around it making the bb more stable in its flight, note, they do not make the bb rotate on its horizontal axis. The performance at 1j, is superior to most 6.04 to 3 tightbores. The answer to your question is nope, they reduce it.

gungun

about the one joule limit, i was thinking today about these barrels and with real steel guns the rate of twist varies at different calibers etc.
if the rate of twist was greater or lower would that make them work on a higher/lower powered gun?( im not making an overpowered gun, i just want to see if twist differences would work)

Firekitten

not sure to be honest... I'm sure others could answer this better... but I'll try.

Essentially the grooves in TK twists are to support airflow. Under 1j. and up to 1j, TKs are at their prime. However, over this becomes slightly more of an issue... Not a 'huge' one, but the efficacy begins to dip. Up to 500 they still show improvement over normal tightbores.... So what would move the peak further up with fps? deeper channels? wider? We run a risk of 'scouring' the bb surface with any more drastic modification to the dynamic of the inner barrel. I think unfortunately, that the TK is a design that can't really be improved in that direction, its certainly not the only way to go in accuracy.

Stercus Accidit

The TK barrels are pure snake oil, don't even bother.

They are sold with the intention that people will recognise rifling as being in real steel, and think its cool to have that in airsoft. Then TK spin some pseudo science, really questionable stuff, to justify it. People want rifiling to work in airsoft, when it really has no place, so they convince themselves its true.

Real bullets spin on their axis of trajectory, this imparts gyroscopic stability, this keeps the pointy end facing into the wind resistance and into the target, with super high velocities, drop due to gravity is minor as your bullet has travelled so far in such a short time, but of course, bullets drop under gravity at range. (ignore bandy computer games)

Airsoft bbs go slow, gravity effects them more at range as they take a long time to get there, hop up adds a back spin to counter act this, like curving a football. Once you have a projectile spinning in one direction, you will not be able to spin it in another way, it would just curve to one side.

TK barrels don't spin a bb, they do nothing to it, rifling in RS works as above, in airsoft hop up is more important, you can only have one or the other.

Just get a regular tightbore, never mind the bling factor of look alike rifling.

Firekitten

think you missed the point there sam... it doesnt spin the bb... misconception.

What they do, is rotate the air around the bb in the barrel maintaining its stability like a much tighter barrel without the chances of a jam. Idiots bill them as rifling, you were right there. But the science is good, and I've seen then out perform regular tightbores tbh.

Phractal

Sam: you are right in saying that conventional rifling is pointless- the BB is spherical, and spherical projectiles never worked as well with rifling as, say, cylindrical with a pointy bit. Also it can only spin on one axis and the hop has done that.
Firekitten: you are ALSO correct. The TK twist barrels have nothing to do with spinning the BB but instead Its all about sealing and such. I think I may be installing one in my JG G36c when it arrives

Stercus Accidit

Firekitten wrote: »

think you missed the point there sam... it doesnt spin the bb... misconception.

What they do, is rotate the air around the bb in the barrel maintaining its stability like a much tighter barrel without the chances of a jam. Idiots bill them as rifling, you were right there. But the science is good, and I've seen then out perform regular tightbores tbh.

Thats the snake oil I'm on about.

TK barrels do not out perform similar tightbore barrels, I have seen the results tested with some degree of scientific process and documented, unlike the claims that they rotate air which is not demonstrated in any way. The results are no better than a tight bore of similar quality.

This idea of rotating air is hogwash, and I hit my point completely, in real steel rifling has a purpose, in TK barrels, it merely has recognition as something cool, and has a makey uppey reason that it is functional.

Masada

Your 100% right sam, I even compared mine with a standard G&G barrel in my MP5 and a Madbull python too, guess what was the best.

Phractal

So Richie... What WAS the best... The Madbull?

I figure the normal JG barrel is grand with a good hopup - rebarreling can come later with a Prommy barrel.

Puding

Prommy barrel.

to be honest go with the mad bull, for the price they can not be beaten

Stercus Accidit

The madbulls are aluminum are they not? Can they stand up to wear and tear, the potential for grit etc making its way in there and leaving a scratch? I've always wondered how they lasted.

Puding

i think i have 4 installed myself and installed a unknown number in aegs at the club, the v1 madbul where not the best, the quality of the aluminum was great the finish used was know to come off, they seem to have fixed this problem with the v2 barrels, personal i've had no problem with them

Phractal

A mate tested both the Prommy and Madbull - he reckons the Prommy is a better barrel - you get what you pay for!

Puding

Phractal wrote: »

A mate tested both the Prommy and Madbull - he reckons the Prommy is a better barrel - you get what you pay for!

tried both myself and i would go with the madbul swings and roundabouts as with everything depends on far more than the individual components, hopup bucking used bb used for starters, an aeg is a sum of its parts as i where, go with what ever works for yourself then

Phractal

Really I think its a matter of personal preferance. I am keeping the JG G36c as stock for a while, working out what are the best bits to put in it - and getting the optimal barrel length - then giving it the 'works'. I think a nice rewiring, MOSFET, V-ROF unit, nice optimal length barrel, Guarder Hopup, and some mods to the cylinder/gearbox unit will be in order - as will the 'pimping' of it with the accessories

Masada

Sam: i haven't had any problems with them in the time ive been using them, they've been the best of the bunch and ive tried various others, including the prommy. (which is still a good barrel though)