AOSC Forum Archive

Alright, Cylinders, ported, non ported, what do they mean, what do they do, how do they work?

Alright, where to start.

Full cylinders. Full cylinders will have as much as as possible behind the bb (almost, Bore-Up cylinder sets will provide more, but the same concepts still apply). They are perfect for your DMR applications. As soon as the piston is released, the bb will start to accelerate down the barrel. The bb will continue to accelerate until it leaves the barrel, or until it runs out of air. With heavier bbs, they will take longer to accelerate up to speed than light weight bbs. Simple physics, a heavy ball is harder to throw than a light weight ball. Because of the full cylinder, you take more advantage of your spring, allowing it to be more efficient, as it has more air to push the bb, it's able to maximize its output when using heavier bbs. Light weight bbs don't see this advantage because they don't have the mass that creates the pressure build up behind the bb. This is joule creep. It's dangerous, be aware of it. Just because your gun shoots at 360fps with .25s, doesn't mean that your .3s chrono at the same power level. Be careful.

Something else to be aware of with full cylinders is over voluming. Not only does it result in joule creep, but it can also mess with your accuracy. Behind that bb is a wall of pressure, when the bb leaves the barrel, that wall effectively explodes out behind it. This is why you see barrels with "crowns" a beveled end. That helps to aim the "explosion" around the bb, to create less turbulence. Crowns are very important for accuracy because of this. Every good system is a least a little over volumed, so there will always be excess air behind a bb. In extreme cases, you create a shotgun effect. But, that's related to super short barrels (<200mm) and a full cylinder. This is also related to why it's so incredibly hard to make an MP5 or MP5k DMR. Having such a short barrel doesn't give bbs time to accelerate like they need to do, especially heavy bbs. You have to use enormous springs to see even a slight increase in fps because of how short the barrels are. In situations as extreme as this, it's not uncommon to have bbs chronoing with the same fps. Imagine chronoing at 300fps with .2s, and then chronoing at 290fps with .4s. That's the kind of crazy stuff we are talking about. When you have a barrel that's only 150mm long, and a cylinder with enough air to blast a .4 through a 500mm+ barrel, you get some crazy stuff. And sure, you've managed to break your MED with something like that, but you also have almost no accuracy. This is a painful realization, that while you have no accuracy, you have almost twice as much power. People who use this to cheat are only out to hurt others. Always, always, always be aware of what your gun chronos at with the bbs you use on the field, especially if you are just under an MED limit. I know the FPS rules of the AOSC don't exactly account for this, but as fair, honorable players, you should be aware of it, and should fix your system, given your abilities, so that if you have joule creep, you do not go over your MED.

I'll hit ported cylinders in a bit, It's purdy outside and I want to enjoy it a bit. Ask questions, and I'll answer them all later this evening when I vomit info about ported cylinders and why you use them.

How does one go about "balancing" the volume of the cylinder to the barrel they plan on using?

Ported Cylinders. A different beast. Weird little creatures that almost seem to have a mind of their own. You see, what a gun will chrono with a full cylinder is likely to be much lower than what it would chrono with a ported cylinder. Now, isn't that weird. A full cylinder puts your .25s at 360fps, but a ported cylinder bumps it up to 400fps. How'd that happen? With a ported cylinder, the piston has more time to accelerate. So when the piston finally hits the air, and starts compressing it to push the bb, it is hitting it with a much higher force than what would be there with a full cylinder. This is beneficial for several reasons with different setups.

For high speed setups, you rarely want a full cylinder. Reason being is exactly what I've already said. The piston accelerates faster than it does with a full cylinder. This mean it reaches its resting point faster, and THAT means that the piston returns to the position it needs to be for the gears to engage it faster. This will help prevent premature engagement. Now, this should never be the difference between PME and not, it will help, but rarely affects it enough if you are already getting PME. But, that is a slightly different topic, perhaps for another time.

You also have less air. After reading above, it might sound like it's always good to have more air, you get more out of your spring. While it's true you get more pressure with heavier bbs, all that air is wasted on light weight bbs. Generally speaking, high rate of fire set ups have shorter barrels than normal. Remember what I talked about, about ALL that air, and a short little barrel? It messes with accuracy, big time. Not really an issue for CQB, but if you plan on using that rifle in a field, it'll put a new definition to spray and pray.

By having a ported cylinder, you can more easily use heavier bbs without going over the fps limit, something you can't easily do with a full cylinder.

There are many different applications for cylinder ports, or the lack thereof. Full cylinders, short barrels, and heavy bbs are a great way to make your gun loud, especially with a barrel that has no crown at the end. That "explosion" of air behind the bb when it comes out of the barrel. Heavy bbs create a pressure spike, full cylinder supplies a large amount of air, and a short barrel ensures that the pressure spike is high when it's released. The lack of crown stops the air from being cushioned as
it goes around the bb, basically creating a choke point, where it rushes out once the bb passes the edge of the barrel, magnifying the pop even more. Couple that with a heavy piston, metal piston head, and a hard washer on the cylinder head, and you'll have one loud, nasty sounding gun.

You also have uses such as balancing your barrel, which leads us toooo.....

Titan wrote:How does one go about "balancing" the volume of the cylinder to the barrel they plan on using?

Balancing your cylinder is a little tricky. Ideally, your piston hits the cylinder head instants before the bb leaves the barrel.

Some things to keep in mind are cylinder to barrel ratio. Generally, this needs to be 1.5 to 2.0, meaning, you want 1.5x or 2x the amount of air in your cylinder as you have in your barrel. This has to do with the bb weight. As your bb goes down the barrel, air escapes around it. The longer it's in the barrel, the more air that escapes. So, .20 gram bbs will leave the barrel quickly, so not as much air will escape around them, thus you only want a lower ratio, like the 1.5. However, .40g bbs are very slow, so they are in the barrel for much longer, and more air escapes around them. To compensate for this, you need more air in the cylinder, thus the 2:1 cylinder:barrel ratio.

So, the barrel is easy to figure out.

((Barrel Bore Size)/2)^2 * pi * (Barrel length)

So for your 6.03mm 363mm barrel, the math would be ((Barrel Bore Size is 6.03mm)/2) * pi * (Barrel length is 363mm) = (6.03/2)^2 * pi * (363) = 3.015^2 * pi * (363) = 9.09*pi*363 = 10366.5 cubic mm. It's really not THAT complicated, but a calculator helps.

It's the same equation for the cylinder, but you just have to measure it a little differently. Cylinders are approximately 24.5mm in diameter. Bore ups are a little larger, for obvious reasons. Now, the length of the cylinder is the hard part. You can't just go measuring the whole thing to see what it is. You have to remember, the cylinder head takes up room, as does the piston head. If the AoE is corrected, that also takes up more room in the cylinder. You are going to need to measure the length of the useful cylinder area with the cylinder head in. You'll want to measure it to the port of the cylinder, or to the very edge, if it's a full cylinder. If it's a full cylinder, you'll have to measure the piston head, and subtract that from the volume as well, be careful to measure it correctly, it could be a little difficult. You'll have your cylinder length now, and you can plug it into the equation above.

For simplicity's sake, let's say you have measured 50mm of room. That could be something like a Type 1 cylinder, or a full cylinder with AoE correction. Anyway, same equation as before. ((24.5)/2)^2 * pi * (50), to just cut to the chase, that's 23571.7 cubic mm.

So, you have a cylinder to barrel ratio of 23571.7:10366.5, or 2.27:1. That's a quite large ratio. But now you know where you stand, and know you know where to move to.

Consider working backwards.

You know your barrel has a volume of 10366 mm^3, You plan on using .25s, so you want a ratio of about 1.6. So, using a little algebra, you'll find that 1.6/1 = (cylinder volume)/10366, multiply each side by 10366 and you'll find that you'll need a cylinder volume of 16585 mm^3. We know that standard cylinders are ~24.5mm, so, once again, we can use a little algebra to find the length of the useable cylinder area.

(24.5/2)^2*pi*(Cylinder Length)=16585
150 * pi * (cylinder length) = 16585
pi * (cylinder length) = 110
Cylinder Length = ~35mm

That's roughly a type 3 cylinder. If you're feeling daring, you can cut the holes yourself, measuring 35mm off of the cylinder head's internal padding. It'll be closer, much better than normal, but still not quite perfect. To get it exactly where you need it, you'll need to start running trial and error to find the perfect spot. However, you will be close enough to negate any over voluming issues, and reduce the noise of your gun. Remember that it's good to be slightly over volumed, differences in air pressure (air density) will affect the ratio. This is a rather dumbed down way to find your perfect cylinder to barrel ratio. The actual methods of finding it are rather complicated, and require a great deal of work and specialized equipment, thus, getting close is good enough.

If you're especially bored, and want to try and get the most performance out of your rifle, you'll need a good microphone, computer that can run audacity, and a piece of hard, thick plastic, metal, something that will make a noise when shot.

Load your gun, turn on audacity, and place the piece of metal/plastic in front of the barrel. Fire one shot (I should mention, it's probably a good idea to have eye protection, and maybe do this outside if possible. Your bb will likely ricochet off of the metal and go somewhere around the area. I suggest doing this in such a way that you won't damage your computer, yourself, or anything else around you. Generally, I'm also assuming the people attempting to optimize their gun in this manner also have enough common sense to be safe). Anyway, fire one shot into that piece of metal. The metal should be RIGHT in front of the barrel. If you have to, remove the flash hider to get as close as possible. It's difficult, but what you are measuring is when the piston hits the cylinder head, and when the bb hits the piece of metal. If you do a little thinking, you will realize this has to do with what I said before "You want the bb to leave the barrel moments after the piston head hits the cylinder head" By using audacity, you can pinpoint when the piston head hits the cylinder head, and then when the bb hits the metal piece, symbolizing when the bb leaves the barrel. If the spikes on audacity are far apart, you'll need to port the cylinder a little further, if they aren't, you might be happy with it. Likely, you'd want the spikes to be touching each other, or almost right on top of each other, as the bb's mark would be slightly delayed because it has already left the barrel when it hits the metal piece.

Of course, this method takes lots of time. You have to completely disassemble your gun, drill the hole in the cylinder, or slightly drop the port, reassemble your gun, test fire it and see where you are. I suggest little steps so that you avoid under voluming your gun. Not having enough air will cause the bb to drastically slow down at the end of the barrel, and your fps will really drop off because of it. It'll also do a number on your accuracy, and you want to avoid that at all costs. Again, a small amount of over voluming gives a little buffer to that happening, and helps to make sure that things run as they should.

Ideally, using this method would negate the use of foam filled suppressors, as they simply absorb the extra air that comes out behind the bb. If the amount of air that comes out behind the bb is negligible, then the mock suppressor wouldn't make a difference. For those that refuse to use them due to legality reasons, this is how you make your gun quiet, without breaking federal laws.

ur rong and u dont no wat u r talkin abut

...but seriously. That was very thorough and an excellent explanation of concepts that are often difficult and time consuming to convey. Thank you for providing such a useful repository of the how and why behind cylinders/barrels/volume/ports.

lol, why thank you Dom. Token and Titan were talking about it in the chat, and it's just too much info to convey in that tiny little chatbox. They wanted to know, so here's the post describing it.

I'm glad you approve

Star_folder wrote:I'm glad you approve

What's that you say? This thread is...

Now is when I wish I didnt suck so bad at math.
Fortunately I am pretty good at audio engineering, so I might go that route.
Amazingly good write up as always Star.

so if eye put dez bore up thing im meh polar star it will make shoot far?

no, uz getz morez fpses. duh.

na d00d its all about dat REAPs bucking, dat thing xtendz yo range to infinity dawg

On a serious note this is very useful information, and might explain why one of my AEG's is more effective at being a shotgun than all airsoft shotguns. Now all I have to do is figure out what type of cylinder I need to match my barrel with out my head exploding. I think it is a type 3 for a 374mm barrel. Any body want to confirm that I did my math right.

Cilenderz are four noobz. Juzt git a pularster.

As a basic rule of thumb.

Type 0 for 509+ (No Ports)
Type 1 for 455 (Ports on the edge of the cylinder, some brands skip right over this kind of cylinder)
Type 2 for 400 (Ports just inside the edge of the cylinder)
Type 3 for 363 (Ports about 3/4ths of the way)
Type 4 for 300 or less. (Ports just above the middle of the cylinder)

I don't think there is a Type 5. As it is, type 4s are half way through the cylinder. I guess, realistically, if you needed anything shorter, taking one of the other types and flipping it around would work, but really, you should never need anything shorter than a Type 4.

lulz u all r stoopid, git da LRB ef u wants rainge

Seriously, good write up, now time to do this for LRB systems

LRB systems, are complicated, more so than cylinders. lol.

Also, using that general rule of thumb I posted earlier, remember, it's just a general rule of thumb. I've used a Type 2 with a 455 barrel without issues. It's got lots to do with how good your compression is, how well everything seals together.

Edit: Moving question to tech talk