A question about barrel length
 

As I look at different models I find that quite often there are guns that come with 3 different barrel lengths, but are otherwise identical internally ( I assume).

I understand the benefits of having a shorter barrel for CQB play, but how much benefit, if any, do the longer barrel sizes give you when it comes to range and accuracy? At what point does increasing length deliver diminishing returns?

Read the part about barrels

http://www.airsoftcanada.com/showthread.php?t=166583

TLDR; longer barrel makes absolutely ZERO difference what so ever at the muzzle energies we play at, it is purely aesthetic.

the size of barrel has two things:
1. where the air window should be places inside your gearbox for maximum performance
2. how much stuff you want to attach to it.

Aside from these points, there is not difference in terms of performance.

When it comes to CQB, I opt for 416 or MP5 as smaller size allow for very good manuver around corner. I have not played outdoor and I am not a sniper.

The best idea is to go to store and hold the actual gun. If you go out to play, ask people about the piece and see if they allow you to hold it for testing.

Here is a definitive answer for you. At least accuracy wise.

You will not see any more accuracy/consistency benefit after 450mm length. This is kind of the sweet spot that allows your spin from your hop up to stabilize but not so much as to start having irregularity down the barrel.

That being said if you need a smaller one for cqb you will probably fine.

Edit: if you're an aeg player you will need to match your cylinder volume. (I'm not an aeg player so I'm uneducated about the subject.)

The length really won't effect the accuracy at all. The quality/consistency of the bore of the barrel and a quality hop rubber and BB'S of a heavy enough weight will.
My mp5k I had, with a pistol length barrel, could shoot as far as my m4 with 510mm inner. Both around 400fps both with promy flat hops. There was maybe a slightly better grouping at max range with the longer barrel. But the stock on the long gun could likely be the difference.

The number you're looking for is 420mm, and that number describes the best possible efficiency of air volume while using a full cylinder. It has nothing to do what so ever with accuracy.

If my pistol can get a 4" grouping at 150ft with it's miniscule 3" barrel, then how will adding another 13.5" of barrel will somehow make that any better?

Guy spends $3000 on a CQBR ptw, there's a reason he spent it on a CQBR instead of a 16" DMR. And that reason is, they have the exact same range and accuracy.

First of all. The barrel length does effect accuracy but no where did I say that is where most of your accuracy comes from. I was adressing what length is best for accuracy and that is all. The optimal length is 450mm, the difference between a 500 mm barrel and a 375mm barrel with be hardly noticeable. I did not adress bore size, hop up, or materials.

The OP asked what length is best and that's the answer.

Not what I'm talking about. See post below

Here is a good article for you.

Sounds like a lot of american bullshit tech blabber to me.
#1 point that gives away the fact he doesnt know what he's talking about is he thinks pistons can cause suck back in high RoF builds.
At 300fps it takes a BB less than 65ms to leave the barrel.
At 60rps thats a 166ms cycle time
And it takes around 30ms for the piston to come all the way forward
That leaves 35ms for the BB to leave the barrel while the gear train is taking 166ms to do a full cycle
There's no suck back. There's a loss of lressure at best but no way in hell you'll ever be able to create a suction force to stop the BB in the barrel to cause a misfeed.

Furthermore, if he thinks that is whats causing misfeeding in high rof builds, then he doesnt understand high rof builds.

I have a simpler explanation that makes a hell of a lot more sense;
Its easier to aim a longer rifle than a shorter one.
Your own personal accuracy is going to be better with a 30" barrel rifle thats hard to swing around versus a 9" barrel rifle thats pointing all over the place.

If his theory had any ounce of truth, then a pistol with a 3" barrel would be very easily notably less accurate at 160ft than a 16" rifle. And yet it's not.

In airsoft, the barrel is only a method to confine air to accelerate the bb. The accuracy and range come entirly from the hop up. The best barrels are the ones that touch the bb the least and if they do, affect it the least.

lol suckback.

There are so many other places to draw air from, I guarantee you it's not trying to suck it back from the barrel.

longer rifle allows for slightly better aim down the sights, sure. Longer guns are far more cumbersome though. Length of the barrel has less effect in airsoft than people are led to believe, I get similar results from my 229mm mp5 vs my 407mm g36.

smoothest, most consistent bore of barrel matters, not length. Quality of airseal and hopup are the most important in getting more precision out of the rifle. Higher weight, higher grade BBs also help.

Anyone that thinks suck back is a thing is an absolute moron. The suck back theory is a poorly thought out idea made by people suffering from tappet plate pre engagement who were too stupid to figure out how to solve the issue at hand. Suck back is not possible because the nozzle breaks the seal with the barrel before the piston even begins to retract. The guy that wrote that has no idea how to build high end AEGs.

As far as barrel length and accuracy goes, most people seem to think 300-450 is the ideal barrel length. I think that that's all blabber. I had a M14 with a 550mm Prometheus barrel. I had setups with 509, 455, 433, 407, 363, 318, 300, 285, 260, and 247mm Prometheus barrels. Accuracy was pretty much the same.

The reasoning for the theory that 450mm is the longest effective barrel length for AEG makes sense, in that after a certain point you run out of air volume and pressure to center the BB in the barrel. If you have a flawless air seal and are shooting 400 FPS or higher, than you can exceed 450mm without detrimental effects to accuracy. The easiest way to determine the longest barrel length your setup can support is to gradually try longer barrels until you stop gaining FPS from having a longer barrel. From 509mm to 550mm I went from 445 FPS to 455 FPS.

I'm not supporting his suck back theory cause I have no knowledge of aeg's but the BB rolling on the top of the barrel theory seems pretty sound to me.

Except that the Magnus effect doesn't work the same when in a tube... Sort of like how the Bernoulli principle is supposed to give F1 racers better traction, but when Ayrton Senna's diffusers touched the ground they stopped working and got him killed.