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Discussion Starter · #1 · (Edited)
Is there any advantage to using longer inner barrels (with correctly matched cylinders, of course). I've heard very controversial reports on this subject. For example, take an SVD with a 690mm barrel vs an AK47 with a 455mm barrel, with both guns having correctly matched cylinders and near-perfect compression. Assume that both barrels are perfect quality and are very straight. Which rifle will perform better? Some people say that past 450mm barrel accuracy will go down, while others say a longer barrel will result in more accurate shots, even though the difference is minimal past a certain length. Does anyone have any test data regarding this?

I've also heard that longer barrels = more fps. Will a longer barrel + big cylinder have more fps than a shorter barrel + small cylinder? Assume C:B ratios for both barrels are ideal and everything else is the same. After all, why do people use long barrels and bore-up cylinders? And a longer barrel makes the rifle quieter, right?
 

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I can confirm that a longer barrel will give you more fps, because the bb has longer to accelerate. As for making it quieter, most of the sound comes out of the receiver section and echoes in the stock, not the barrel. A longer barrel if anything will just add a few more vibrations to hear, though you probably won't be able to notice it. (Pretend this is a new pararaph lol.) Barrel size past a certain point will not increase accuracy.With a properly tuned hop, you will see no difference between the accuracy of a g-spec vsr and the pro version. The only thing the longer barrel of the pro version does is add some LRB freedom. Of course a barrel does stabilize the hop somewhat, like with an LRB, but having an uber long barrel can only hinder mobility. People use bore-up parts because they are either obsessed with fps or have the misconception it will give a more stable hopup somehow. Realistically, if you already have that bb going straight and you already applied hopup to it, more barrel to keep the bb centered won't accomplish anything. I think there is a stickied post about this somewhere but I don't feel like searching through posts.
 

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@Chach- With all those free fps mods out there (there is even a whole big write up on them stickied somewhere) it really isn't worth it. Just get a batter spring if you really want that extra kick which serves no purpose either. Past a certain point, fps does nothing for accuracy (assuming hopup stays consistent). You'd just be throwing money at your rifle to get slightly more fps out of it. Forgetting about the caps, it won't do you much good anyway. The only thing that affects accuracy is the hopup. You can whack the bb with a baseball bat and it will go straight, but that backspin is what keeps it level, and keeps it steady in the wind. (New paragraph.) @Sand- for the most part, the mainstream rifles already have optimized volumes. It also depends on fps though, as mentioned in the sticky two from the bottom, labeled something along the lines of "the airsoft trajectory project" or something. The post also tells you how to find the optimized volumes, or at least a generalization of them. Sorry for the long posts, lots of info.
 

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Discussion Starter · #6 ·
Ahh, that's interesting. I suppose an AK47 shooting at 450 fps will have the same performance as an SVD shooting at 450 fps, assuming they have the same internals besides cylinder and barrel, but the AK47 would need a heavier spring to achieve the same fps as the SVD. Interesting how people who want to upgrade their rifles to DMR's always go for the longer barrel.

But are you sure longer barrel doesn't make a quieter gun? Based on my experience, I'm almost positive that it does. To me it makes sense, as a longer gun means more "stuff" to absorb the sound.
 

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There are some other advantages, but accuracy is not inherent.

A long barrel with the same spring can give more energy to a heavier BB than a lighter, which can be quite beneficial.

Putting energy into the ball means a quieter shot too, since the pop at the end is the extra energy blasting out the muzzle after the ball. For instance, my DMR makes practically no noise but the gearbox's turning. It makes less noise when dry-fired with the barrel in than with no barrel too.

I use a long barrel because that is what the gun demands.
 

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Oh, a wider bore might provide more power, since there is a bit of mechanical advantage to putting a wider volume through a smaller aperture, as how mechanic's hydraulic lift works.
 

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I suspect because the air has expanded in the barrel and is a touch less sharp, slower when it comes out. Or, it just might be the shape of the body when the barrel is out is like a trumpet mouth.

Anyway, heavier balls take energy that could be used to make noise in stead.
 

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Discussion Starter · #15 · (Edited)
Interesting. From my observations, I can still say that a longer inner barrel (generally) makes a quieter gun. Maybe this is because the air isn't escaping through the ports in the sides of a ported cylinder which is used for shorter barrels?
 

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Discussion Starter · #17 · (Edited)
I really think it is just the length allowing more energy to go into the ball and less into the air at the muzzle.
Alright, I did my own research. It turns out that a longer inner barrel + larger cylinder generally means a quieter gun because:

"Another thing to note is that longer barrels tend to give a quieter "muzzle blast" if you will, because of the increased expansion room within the barrel. Even properly volume matched, a gun with a shorter barrel relies on using a low-volume high pressure burst of air which expands much more suddenly within the barrel. The longer barreled guns have more space to accelerate the bb, and thus the air leaving the cylinder is at a lower initial pressure and loses its pressure more gradually since it accelerates the bb over more distance."

taken from
http://freedomairsoft.forumotion.com/t72-aeg-silencing-guide

Also, Noobie did a test regarding barrel length vs. fps. He matched a 500mm barrel and a 313mm barrel with cylinders which provided peak efficiency for the two barrels (all other components being the same) and found out the 500mm barrel got 520 fps, while the 313mm barrel got 510 (although he did say that he could have improved his C:B ratio for his 500mm setup by a little, so maybe the difference is a little more). He then upped the spring power on both guns and found the longer barrel shooting 18 plus fps harder. So I guess the FPS difference between barrel lengths is actually quite minimal. Noobie also said that there was no difference in accuracy between the two barrels.

taken from:
http://www.airsoftretreat.com/forums/index.php?topic=88662.0

So in conclusion the advantage of using a longer barrel and larger cylinder is decreased noise (the "pop" of the BB being fired, not GB noise) and (very slightly) increased fps efficiency. I find it interesting that a longer barrel won't do much for accuracy or fps, although I guess a few free fps wouldn't hurt anyone!

Here is an example of what I just said. It's a chrono of the Echo 1 AKM and the Echo1 RPK. I'm pretty sure that they use the same spring and have similar internals, although the RPK probably has a larger cylinder. You can see that the RPK is shooting slightly (5-10 fps) harder than the AKM, and it is also has less of the "pop" noise while firing because of its 590mm barrel.
 
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