Barrel length effects on accuracy - Breakdown and recommendations

[jack25]

Barrel length should have no effect on accuracy, but I'm not sure.

 

[Pseudotectonic]

I think ultimately it depends on the context and detail of the question.

Are you asking about a physics problem, where all other variables including cylinder size and spring and hop are unchanged, would simply a longer or shorter barrel affect accuracy? Yes, because changing the length would unmatch the air volume, which affects fps, in turn affect reach, and then accuracy. Is it day and night difference? It will not be day and night difference, if your barrel length is not day and night difference.

Are you asking about swapping a different length barrel on the same gun, while re-tune the cylinder and hop so that the fps is unchanged? Probably depends more on whether your tech skills can tune it to the same fps and hop. Anecdotally a shorter barrel feels more accurate (see above comments) but it is unknown how air volume factor into this, and whether it is measurably more accurate in a target grouping test. Therefore, in the same gun, the effect of the absolute length of barrel is negligible and unpredictable, because of all these other variables you are inevitably changing at the same time. Some might say it makes "no difference" in a practical sense. Unless you are doing something extreme, of course. Incidentally polishing the same barrel will make a bigger improvement than swapping to a longer or shorter barrel, so is changing hop rubber, or use a heavier BB; barrel length is the last thing you need to worry about, when upgrading the same replica.

Are you asking about choosing between two entirely different guns with two different barrel lengths, like an MP5 vs an AK? Or a pistol vs sniper? Now the pool of variables are even bigger, because ergonomics, skills, play style, and even situations where you use them would be so vastly different it would be comparing apple and orange. Even if they all shoot the same fps, the difference in weight of the replica alone would probably make a greater difference in your aiming posture and control than say the barrel length difference. So the barrel length difference, in this question, is quite irrelevant.

 

[Pseudotectonic]

Bonus question:

In a physics problem, comparing two barrels, one longer and one shorter, assuming in both situations the BB will exit with the same velocity of 300 fps while spinning at the same RPM for hop, would the longer or shorter barrel provide more accuracy? This is an unsolved problem, both theoretically and experimentally. In pure geometry a longer barrel should suggest a more precise exit vector with less angular variation, however the question of BB ballistics inside the barrel is a complex situation combining the Magnus effect, Bernoulli's principle, Coanda effect, harmonics, interactions of plastic vs brass (or steel), and inevitably the probabilities of defects and surface finish variations, etc. We are still very far from a comprehensive theoretical model that describes everything that happens in this simple system, and as far as I know no one has done such an experiment. So really it is still up to debate.

 

[ParHunter]

Is there somewhere a formula in matching your inner barrel to your piston and spring?
I understand that the volume of the cylinder (the active part - how do you actually figure that out? I guess you could measure how far you pull back the bold handle) should be higher than the volume of the inner barrel but by what factor?

And how does the spring come into the equation?

I got a TAC41 LS and I was told the barrel is too short for the gun and I should get a longer barrel for it. And that was mentioned as the first improvement I should do. Apparently I could go down to the weaker 100NM spring and pretty much achieve the same distance but with better accuracy. They also mentioned that the bb would be pushed offline when the air pressure is too high when the bb exists the inner barrel.

On another note, would it be possible to 3d print a ‘compensator’ with build in barrel extension? I guess you would not be able to get a good air seal. 

 

[Pseudotectonic]

@ParHunter Very roughly this is a guide for voluming, generally you want to follow a rough ratio of say > 2. The cylinder volume is just literally the cylindrical shaped block of air, inside the cylinder, in front of any port opening on the cylinder. That is the block of air that is being compressed when the piston slams forward.

Stronger spring can compress a certain air volume faster, which gives the BB more acceleration, thus fps. (In car: how hard you press the gas)

A bigger air volume, will accelerate the BB for longer (given a long enough barrel to make use of it). (In car: how long you hold the gas)

You can accelerate to a certain speed by pressing the gas harder, or by holding the gas longer. If you press hard enough, you can get to a high speed using less runway distance. And if you have a long enough runway, you don't have to press the gas as hard, you can just hold the gas for longer, so when you reach the end of the runway you would have gained enough speed.

 

[ParHunter]

Thanks for the link @Pseudotectonic very helpful! I understand that a stronger spring would compress the air quicker and thus provide more acceleration. I was just wondering whether the spring comes into the equation for determining the optimal barrel length but it seems not.

 

[Sewdhull]

You will note that there is no optimum barrel length for a cylinder volume, there is a range of ratios and this is because of the other variables, air pressure loss and starting pressure, BB mass, hop setting, barrel bore and general quality. Also what your goal is for the system.

Ratios quoted like 2 to 1 etc are to allow there still to be useful pressure in the system so the BB is still accelerating in the barrel, still supported by an air cushion. In this case and any case where there is more than 1 to 1 ratio(without losses), a stronger spring will allow more energy to be imparted to the BB in the same length of barrel or keeping the same spring allow a longer barrel to absorb more energy in a longer time or combination of the 2.

In a zero loss system with 1 to 1 ratio there would be no purpose in a longer barrel, regardless of spring strength because altho average pressure would be higher it would still be atmospheric when the bb left the barrel.

I too enjoy flecktarn kit.

 

[ParHunter]

Given the calculator @Pseudotectonic linked to I’ve established that the ratio for my TAC41 LS is 4.32 with the 330mm barrel (the volume of the cylinder is quoted as 41cc). That sounds way too high. Even with a 440mm barrel it is still a ratio of 3.25.

I have yet to play with the TAC41 or shoot it at any distance further than 10m so I have no idea how she actually behaves on the field so I won’t go ahead and order a longer inner barrel just yet (which Airsoft retailer is best for parts?) but I would like to plan ahead.

Coming back to my idea of printing a ‘silencer’ with a build in barrel extension (probably not at 6.05 but a bit wider). I didn’t study fluid dynamics but I could imagine that it would be very easy to create turbulences and make things considerably worse. Am I right with my guess or could a little gap between the inner barrel and the barrel extension actually ‘release’ some of the excess pressure without creating turbulences around the BB?

Update: 

ChatGPT shot down my idea saying that it would indeed create turbulences. So would probably go down the route of a longer inner barrel which would be concealed by a suppressor. 

 

[Adolf Hamster]

Given the calculator @Pseudotectonic linked to I’ve established that the ratio for my TAC41 LS is 4.32 with the 330mm barrel (the volume of the cylinder is quoted as 41cc). That sounds way too high. Even with a 440mm barrel it is still a ratio of 3.25.

I have yet to play with the TAC41 or shoot it at any distance further than 10m so I have no idea how she actually behaves on the field so I won’t go ahead and order a longer inner barrel just yet (which Airsoft retailer is best for parts?) but I would like to plan ahead.

Coming back to my idea of printing a ‘silencer’ with a build in barrel extension (probably not at 6.05 but a bit wider). I didn’t study fluid dynamics but I could imagine that it would be very easy to create turbulences and make things considerably worse. Am I right with my guess or could a little gap between the inner barrel and the barrel extension actually ‘release’ some of the excess pressure without creating turbulences around the BB?

Update: 

ChatGPT shot down my idea saying that it would indeed create turbulences. So would probably go down the route of a longer inner barrel which would be concealed by a suppressor. 

if you mean the suppressor causing turbulence, i can't say i ever noted an accuracy penalty from running one.

that is, as long as you skip the fart flap, that'll make a barn door an optimistic target from inside the barn.....

 

[ParHunter]

if you mean the suppressor causing turbulence, i can't say i ever noted an accuracy penalty from running one.

that is, as long as you skip the fart flap, that'll make a barn door an optimistic target from inside the barn.....

It wasn’t about the suppressor but printing an inner barrel extension inside the suppressor when you can’t achieve an air seal between the inner barrel and the extension.

 

[TrooperX]

I had one of the original JG G36Cs back in 2000andsomething.  What’s that, a 250mm inner barrel?  The range and accuracy was insane. There just seemed to be a sweet spot with the overall set up of a lot of those back then.

 

[Adolf Hamster]

It wasn’t about the suppressor but printing an inner barrel extension inside the suppressor when you can’t achieve an air seal between the inner barrel and the extension.

Ahh, yes that won't really be much benefit, getting the join to line up well enough to not mess up the accuracy isn't really practical.

You'd be better off with no barrel extension and just an empty can

 

[Cannonfodder]

 I've had some pistols with barrel extensions and I never used them as they ruined accuracy.

I don't know if them being GBB rather than AEGs makes any difference but I guess not

 

[EDcase]

Given how sensitive accuracy is on inner barrel quality, its almost impossible for two barrels to screw together perfectly enough.

 

[Sewdhull]

Given how sensitive accuracy is on inner barrel quality, its almost impossible for two barrels to screw together perfectly enough.

I d agree here, alignment of the barrel would be really tricky.