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Yea the formuli for calc. the opt. barrel length is based on .2g and does not account for certain magic things i don't even know about and there is a lot missing still, for it to work streamlined.. EDIT:Update might be coming up as i'm reverse engineering some of HS5's formulies, will e-mail him 'bout it as well.
Hey Peteralan, that makes two of us, i actually made some progress already, i made it so you can input bb weight and in a crude way include air loss between the bb and the barrel. One big thing i'm still missing is a proper calculation on how the spring transfers it's energie to the bb.
 
very nice ! I get it (I already was aware of this ratio importance) but you explain it very well, it mainly depends on the weight of the bbs, so with heavy bbs, you don't need such a long barrel as with lighter bb's...
 
Super nerd alert, you've gotten me on a roll now. Okay, so first off, thank you Reliku for an awesome thread. I feel like with a little work we could have every last bit of this physics figured out into a comprehensive guide to airsoft sniper tuning. I have a SW M24 that i'm determined to bleed dry of every last bit of performance. So, stay tuned for some additions to this epic thread. Hoping to have a few spreadsheets put together with FPS, barrel lengths, cylinder sizes, bb weights, hopup types, cylinder head types, etc. Btw, there is little info out there regarding actual cylinder dimensions. Could a couple people maybe toss out their rifle models with the measurements? I'm thinking that the stock space on the bottom of many cylinders will also come into play. We'll see. Again, epic thread.
 
Your best bet is this:
0.3gm bb use a 554mm barrel (15821 mm^3) = 2.26:1
0.32gm bb use a 530mm barrel (15136 mm^3) = 2.36:1
0.36gm bb use a 500mm barrel (14279 mm^3) = 2.51:1
0.4gm bb use a 470mm barrel (13422 mm^3) = 2.67:1

0.43gm bb use a 430mm barrel (12279 mm^3) = 2.92:1
0.45gm bb use a 400mm Barrel (11423 mm^3) = 3.13:1
How do you arrive to those conclusions? I ask because I'm getting a stronger spring for my rifle and also want to use heavier BB's.

After reading this thread, I feel like I may be limited to getting .32's or maybe .36's ?

I have the M24 from A&K which has (apparently) quite a long barrel at 520mm
It also has a barrel cap at the end which I think looks nice and provides additional support for the inner barrel. So my inclination is to keep it, especially since I bought a PDI tightbore made specifically for it.

With all that in mind if I increase my stock setup w/ a new spring to create 500fps using .2's ... what does that mean in the end? Like if I get 400-420fps now, and I increase the force, it will negatively impact my using heavier projectiles?

It's like the more power you have and the heavier bb's you use, the barrel length according to you and others is that length needs to goes down significantly. So if I put .4's or .43's in my setup the theory is that my accuracy will go down the toilet.

Just add to the picture I'm currently using .3 bio's and I'm not ultra-happy w/ the accuracy. Because of leaves falling etc I have been able to re-test the accuracy of my setup and I can hit a chest-size target including shoulders at 135ft all the time - but I can put a target at 95ft and the spread is like 8-12" which isn't that great - so extrapolating that at further distances like 200ft my confidence hitting anything man-sized w/ consistency is low. I feel like a lot of guys on this board would have no problem hitting 200ft 8/10 times if not more.
 
I agree Fatman. I don't see a logic to the barrel length stuff either. The only advantage that a shorter barrel has is more joule creep (aka inefficiency with a light BB).

This thread is a lot of calculation to satisfy a number that has not been proved or defined in the real world very well. No offense meant, i just think it misleads peoples time.

I run .43 and .50 through a 555mm barrel. If i could snap my fingers and magically decrease barrel length, i don't think it would make the gun more accurate or harder shooting.
Granted, the increase in power is marginal as you increase the barrel length, but it's not detrimental IMO.
The biggest reason for me to run a long barrel is simply that it reduces the muzzle report, and i like to poke my barrel through brush. Shooting a .50 at 2.5J, the BB in the air makes more noise than my rifle :)
 
Discussion starter · #108 ·
The cylinder:barrel ratio theory is pretty dated because it doesn't account for piston travel length, piston travel time (and thus piston mass, spring power) and stuff like that. For VSR cylinders the ratios are pretty accurate because they're acquired by empirical data through testing, for different cylinders the optimal ratio is more like an educated guess. If you want to be absolutely sure, take your setup and shoot different bb weights through the gun, and test which weight ends up having the most kinetic energy.

Length alone doesn't say much. A longer barrel is theoretically more accurate because the projectile has more time to speed up, but that's only true as long as there is pressure behind the projectile, so there needs to be enough cylinder volume to support the length. Heavier bb's benefit from more volume (as explained in this thread).

So, don't be fixated on length. Compare your cylinder volume to your barrel length and you'll have an educated guess about what bb weight is optimal. Then again, you don't want to be shooting .32 unless you're restricted to crazy low fps and can't go any heavier. If it's for sniping, .4+ is preferred (assuming you've got 500 fps or more at your disposal). Once you're picked a bb weight (according to what fps rules you'll have to comply with), you look up the optimal ratio (for example: 2.7:1 for 0.40 gram bb's) and you determine your cylinder volume. Once you know the cylinder volume and the ratio you're aiming for, you buy a barrel with the length fitting those numbers, and then you've got the optimal setup for your fps: the heaviest bb you can use, with the optimal cylinder:barrel ratio for that bb.

If your barrel is longer, you'll need a less powerful spring and your muzzle noise will be less, but you'll see less joule creep.

If your barrel is shorter, you'll need a tougher spring to keep the same fps, without any real advantages.
 
This thread is a lot of calculation to satisfy a number that has not been proved or defined in the real world very well. No offense meant, i just think it misleads peoples time.
You will find that the cylinder to barrel ratios from the VSR were originally done by me. These are what most people use. So these here:

0.3gm bb use a 554mm barrel (15821 mm^3) = 2.26:1
0.32gm bb use a 530mm barrel (15136 mm^3) = 2.36:1
0.36gm bb use a 500mm barrel (14279 mm^3) = 2.51:1
0.4gm bb use a 470mm barrel (13422 mm^3) = 2.67:1
0.43gm bb use a 430mm barrel (12279 mm^3) = 2.92:1
0.45gm bb use a 400mm Barrel (11423 mm^3) = 3.13:1

To come up with these numbers I did over 100 hours of experimenting and these are accurate. They are not made up and they do apply to real world situations. So these numbers have been proven. I do have charts for the VSR that if I get time, I will post them up. But the important info is that these cylinder to barrel ratios produced the most energy with these bb weights.
 
Is this just a thickly veiled joule creep thread?
Getting the correct cylinder to barrel ratio will definitely help with JC but that is only one reason why you want the correct ratio. With an under volumed system, there will be a negative pressure behind the bb and this can cause the bb to vibrate as it goes through the barrel causing inaccuracies. So getting the right ratio is mainly about accuracy and efficiency for a certain bb weight.
I once used an M170 spring in a VSR10 and a 690mm long inner barrel. When firing 0.2gm it chronoed somewhere around 650fps (3.9 joules) which seems awesome but once I tried it with a 0.45gm bb, it would only shoot about 20 meters before it would flick off into any direction. Normally, it would flick straight to the ground. So I would have never been able to hit a target. This was caused in my opinion by the massive lack of volume in the system.
 
Getting the correct cylinder to barrel ratio will definitely help with JC but that is only one reason why you want the correct ratio. With an under volumed system, there will be a negative pressure behind the bb and this can cause the bb to vibrate as it goes through the barrel causing inaccuracies. So getting the right ratio is mainly about accuracy and efficiency for a certain bb weight.
I once used an M170 spring in a VSR10 and a 690mm long inner barrel. When firing 0.2gm it chronoed somewhere around 650fps (3.9 joules) which seems awesome but once I tried it with a 0.45gm bb, it would only shoot about 20 meters before it would flick off into any direction. Normally, it would flick straight to the ground. So I would have never been able to hit a target. This was caused in my opinion by the massive lack of volume in the system.
so if you were to compare an L96 cylinder (aps2) volume to a VSR one, which is typically bigger?

All things being equal, wouldn't the cylinder volume be irrelevant if you have a joule/energy reading from the piston head? So for example if I get 4 joules out of my piston head, that alone, I would imagine would determine if my barrel is too long.

Basically the whole motivation of my post was I want to keep my longer barrel and was a bit disappointed to learn that I may not be able to have great accuracy 'no matter what'. So if I buy say an s170 spring and shoot .4's compared to my stock spring and .3's - I may not be more accurate and may indeed be less accurate. Would you say this could be the case?
 
Discussion starter · #113 ·
All things being equal, wouldn't the cylinder volume be irrelevant
No. Check out the opening post in this thread, because that's what it's all about.

Why would you want your inner barrel to be long? You can always put a shorter inner barrel in a longer outer barrel, if you want a long barrel for looks or to poke through bushes. Long inner barrels are usually not good for anything, the only thing they really cause is reverse joule creep or in the worst case scenario as described by 1tonne, a loss of accuracy. Match your barrel length to the cylinder according to the bb weight you want to use, that's going to give you the optimum. If you go shorter, you'll need a tougher spring, if you go longer, you may see your performance suffer.

A type 96 cylinder has about 28 cm^3 and a VSR cylinder has about 35 cm^3. Even though the type 96 cylinder is smaller, they can use longer barrels because the piston travel length is longer compared to the cylinder diameter. This is a prime example of the volume not being the only variable influencing efficiency.

For both guns, a 400-450 mm barrel is optimal for .4-.45 bb's. Assuming a standard cylinder without an airbrake.
 
I would need to see, and repeat myself, a lot more about long barrel = less accuracy theory before i would accept it as a conclusion i can work from. I haven't seen any pattern indicating this before, but i haven't looked for it either yet.

How did you arrive at the conclusion that the BB vibrates in the barrel? You would need a transparent barrel and a highspeed camera, maybe even multiple (x/y).
Wax build up in the barrel can be caused by many other things, and is not an indicator.

As long as a longer barrel shoots harder, that is more optimal. If joule creep is the goal, that should be clearly presented with the data. Also there are other ways to make joule creep, far beyond the normal 20-40% difference on a gspec.
The data presented is simplified too much, making people think that shorter barrels are necessary, where as, at best, it is just the same performance as a long barrel.

A longer barrel will always give an overall better result, unless you want to chrono low on 0.20 and high on .45, or believe that a longer barrel decreases accuracy (i am not disputing the possibility of this, it's just too farfetched without proof yet). In Scandinavia, and any site where i have a say in the rules, we always chrono people as-used. Hopup set and with the BB they use. So joule creep is irrelevant as a performance factor here.

Again, there are too many factors to just say "X length is optimal".
My rifle is better with a longer barrel because it reduces the muzzle puff and makes it shooter harder (or rather, i use a weaker spring. So it is more quiet, easier to load, shakes less and wears less).

It is a tiny test sample, i can only work on so much at a time, but i have tried 300, 400, 500, 550mm barrels in my VSR, and it shoots exactly the same precision wise with all those barrel lengths. But there was definately a decrease in power. I cut a 500mm barrel down in steps and measured the power output. It drops very little, but it does drop. Progressively the drop is more and more. But maybe my VSR is not precise enough to truly show the details, i don't know. It does torso shots at 80-90m if the conditions are right (2.5J 0.43, 2m overhold), and headshots at 50-60m. I am sure it can be better if i improve it. I am not satisfied with the result yet...;)
I have switched between full-length springs and springs that are cut so short that the piston is loose for 1-3cm (no pressure!), and it still shoots the same. However, it becomes incredibly silent when done so. It reduces the pressure at the end of the stroke.
 
I would need to see, and repeat myself, a lot more about long barrel = less accuracy theory before i would accept it as a conclusion i can work from.
Your best bet is to do some experimenting yourself and then find out that the info given is correct.
When doing your experiment, remember to measure in joules using the bb weight that you desire.
The old way of measuring is by firing a 0.2gm bb but this is not a true indication of the energy coming out of the muzzle.
 
Discussion starter · #116 · (Edited)
Let me put it this way:

I have never seen a short barrel having a negative effect on accuracy.. However, I have seen long barrels having a negative effect on accuracy.

While there is insufficient knowledge to truly explain that phenomenon, I do think it's there if you make the barrel excessively long (beyond 550 mm), depending on cylinder volume of course.

However, that's not the only aspect. The other aspect is efficiency, so how much energy from the spring actually ends up in the bb. This depends on many factors, but the cylinder:barrel ratio has some (pretty significant) influence on it. This has been shown empirically by 1tonne's data (and other people after him), and if you test this yourself you will find roughly the same numbers.

If your barrel is long compared to the cylinder, it will gain high efficiency with .2 bb's. However:

If your muzzle energy with .2 is higher than with .4, then your ratio is more suited for .2 than .4. It means the maximum efficiency point of the .4 is still inside the barrel. Which means the .4 at one point experienced a higher force in front of the bb than behind the bb, which caused it to stop accelerating, and it started decelerating.

Now I don't have a correct physics explanation of what happens then, but since it does happen (as shown by lots of empirical evidence), I can only imagine it has some effect on accuracy as well. And something like this probably isn't going to positively affect accuracy.

Which reinforces the phenomenon airsoft techs have observed for quite a while: shorter barrels are better when using heavy bb's.

If you're trying to get maximum noise suppression, or if you only care about fps with .2, then yes, long barrels work well, but in the real world fps with .2 doesn't matter, and while noise suppression does, there are different methods to suppress a gun without lowering its muzzle energy with heavyweight bb's and potentially affecting accuracy.

That's my view on it.
 
Your best bet is to do some experimenting yourself and then find out that the info given is correct.
When doing your experiment, remember to measure in joules using the bb weight that you desire.
The old way of measuring is by firing a 0.2gm bb but this is not a true indication of the energy coming out of the muzzle.
I can't help but feel that you've not properly read my post. Almost every post i make, in various threads, highlights that people should chrono correctly instead of with 0.20.

Look in the post above:
Jeppe said:
A longer barrel will always give an overall better result, unless you want to chrono low on 0.20 and high on .45, or believe that a longer barrel decreases accuracy (i am not disputing the possibility of this, it's just too farfetched without proof yet). In Scandinavia, and any site where i have a say in the rules, we always chrono people as-used. Hopup set and with the BB they use. So joule creep is irrelevant as a performance factor here.
I already tested. I have build thousands of guns, altough not VSR's, and the pattern you indicate, i have not seen. "Barrel suck", in it's many forms, is a myth. I've build 500fps (and higher...) highspeed rifles with fairly long barrels. The only issue is the eventual PME/tappet-PME when you push the ROF limit.

The problem is that there is no surrounding explanation for what "optimal" means. Yes there is words, but no actual connection for why the number has the amount it has. So you make a lot of data, boil it down to a simplified conclusion, and then people run with it. If you've done a lot of work and recorded the results, i respect that, and i would love to see the charts posted. I don't deny that the energy difference between, say, 450 and 550mm can be negligble, and it could be considered to basicly plateu with heavier weights, but if the longer barrel shoots harder, it is more optimal! Accuracy being a seperate point.

Let me put it this way:

I have never seen a short barrel having a negative effect on accuracy.. However, I have seen long barrels having a negative effect on accuracy.

While there is insufficient knowledge to truly explain that phenomenon, I do think it's there if you make the barrel excessively long (beyond 550 mm), depending on cylinder volume of course.

However, that's not the only aspect. The other aspect is efficiency, so how much energy from the spring actually ends up in the bb. This depends on many factors, but the cylinder:barrel ratio has some (pretty significant) influence on it. This has been shown empirically by 1tonne's data (and other people after him), and if you test this yourself you will find roughly the same numbers.

If your barrel is long compared to the cylinder, it will gain high efficiency with .2 bb's. However:

If your muzzle energy with .2 is higher than with .4, then your ratio is more suited for .2 than .4. It means the maximum efficiency point of the .4 is still inside the barrel. Which means the .4 at one point experienced a higher force in front of the bb than behind the bb, which caused it to stop accelerating, and it started decelerating.
No, this conclusion i do not agree with. If what you say is that a, for example, 2.5J 0.40 550mm VSR has the barrel cut down to 400mm, it will become maybe 2.6 or 2.7J instead, then i don't agree.
A heavy BB will not increase speed by having a shorter barrel installed in the gun, in my opinion.
Build a long gun (550mm barrel in a gspec or something), testfire, cut the barrel down, testfire. Speed will decrease (progressively more and more), not increase. This is the best way, as to not effect airseal, hopup setting, seating etc.

I'm not trying to be an ass just for the sake of it. I would love to be proved wrong in my assumption, i would immediately change viewpoint, but it requires a lot factor-elimination before i draw conclusions. Reliku can attest that i notice the details ;) and thinks quite creatively.
 
@Jeppe When the piston is done pushing air out of the cilinder but the bb is still in the barrel and the air in the barrel behind the bb is not expanding anymore, what is the bb doing from that point on? Continuing to accelerate, decelerating or acting outside the laws of physics?
Say the bb came to that point at 400mm but the barrel is 550mm and lets say the bb is decelerating for the rest of the way, what will cutting the barrel down to 400mm do? (keep in mind that the bb will touch the inside of the barrel in a bad way with out an air cushion behind it, resulting in extra friction.)

Extra note: Where this point in the barrel is depends primarily on cilinder volume, bb weight, spring strength and barrel bore diameter.
 
Jeppe no ofense man but I don't know why are you so ignorant at simple explanation. Look at it like this: piston pushes air through cylinder and out through nozzle, air is compressed with pressure greater than atmospheric, pressure (P) on area (A) behind bb equals force (F) or F=P/m, by newtons 2nd law object on which constant force is applied will have constant acceleration (a) or a=F/m , so it is simple physics it you have long barrel and you run out of air thus force to push bb out of barrel friction and air resistance will slow down bb more since they are acting in opposite direction and bb will have lower velocity and thus kinetic energy (E=(mv^2)/2). Lets say you use shorter barrel and you don't run out of air, you will have constant force (greater than friction and air resistance) to push bb out of barrel and your bb will leave barrel with higher velocity and this higher kinetic energy.

Next , if you wonder how can friction from barrel surface act on bb? The answer is simple, magnus force. That is the same force that is applied through hop up to negate force of gravity and give bb flatter trajectio. Ever tried over hoping bb? I which direction will go? The answer is upwards. Also lrb(long range barrel) mod (used before invetion of hopup) was working on principle that you bend last third of your barrel down by few milimeters and bb bounce on top of barrel and friction was creating magnus force, lot weaker than hop up of today but still it achieved greater range than rifles without that mod.

And from empirical point of view, I've build well aws l96 (small volume cylinder, 320 mm inner barrel 500 fps) and it had the same range and almost the same energy as my well aps2 l96 (big volume cylidner, 509mm inner barrel) with 0.4 bb's , precision was also the same.

Do not be ignorant to science or physics, it's all around you ;) :yup: :cheers:
 
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