Barrel Length

[Kupalranger]

Hi, I'm not sure if there's a thread for this but

Does changing the barrel without changing the internals bad for the gun? Let's say, a 363mm barrel is changed to a 455mm barrel. Would that have more negative effects on the gun the positive? Would it decrease my fps by a lot?

thanks =)

[Styrak]

Doing that change won't have much effect. Going to a 500+mm barrel will have effects. They can be lowered FPS, and other effects because the cylinder isn't matched to the barrel. You shouldn't have a ported cylinder with a barrel 455mm (AK) and above.

[Short Round]

Originally Posted by Styrak

Doing that change won't have much effect. Going to a 500+mm barrel will have effects. They can be lowered FPS, and other effects because the cylinder isn't matched to the barrel. You shouldn't have a ported cylinder with a barrel 455mm (AK) and above.

Listen to this guy ^^^^

I get a FPS drop every time I use my 433mm barrel in my gun (which is upgraded for a 247 barrel) probably by 20-30fps.

So I suggest if you do plan on using a longer inner barrel (as your primary barrel) just upgrade the cylinder to match it as well.

[Kos-Mos]

Originally Posted by Najohn

Listen to this guy ^^^^

I get a FPS drop every time I use my 433mm barrel in my gun (which is upgraded for a 247 barrel) probably by 20-30fps.

So I suggest if you do plan on using a longer inner barrel (as your primary barrel) just upgrade the cylinder to match it as well.

You case is extreme a bit... going from the smallest to one of the longest...

To OP:

You are better buying a good quality tightbore in the original length and have "perfect" match than getting a longer barrel.

Length of the barrels make little difference unless you add quite long.

[HackD]

Just an example - changing inner barrel length from a stock ICS 363mm to a 262mmx6.04mm (from 14.5" down to a 10.3" setup, both on an M110(?) spring). No other internals changed at the time. FPS went from ~384fps to ~371fps.

[JLiang]

The thing is, cylinder type must be changed if your barrel length is changed.

There's a lot of math involved, of which you can go as any senior member (I personally am not going to bore the crap out of everyone with the details). Basically, the volume of the cylinder must match the volume of the barrel in order to achieve maximum results.

Think about it like this. If you have an amount, say, 60 mm cubed worth of air volume in your cylinder. When your piston pushes it out down the barrel, that volume should be enough to get the BB out, and just that. Too much is not good, and too little is not good, either.

We'll use the previous example. If you have a cylinder that has 60 mm cubed of volume, and your barrel has 70 mm cubed of volume, the amount of air in your cylinder has run out before your barrel has. Therefore, the BB becomes 'stuck' in equilibrium. In layman's terms, your BB now has to 'suck' air in order to continue going.

That was an example of a barrel being too long. If a barrel is too short, say, 40 mm cubed of volume (All these numbers are hypothetical, by the way), your 60 mm cubed of cylinder volume is not yet empty by the time the BB has left the barrel. This results in overpressure, and the excess air continue to buffet the BB after it's left the barrel. This results in unstable flight, reducing accuracy, and potentially the life of your gearbox.

GENERALLY, and I repeat, GENERALLY, the pairings of Cylinder Type to Barrel Length should be as follows:

Type 0: (No hole) 450mm+.
Type 1 (Tip hole) 350-450mm.
Type 2 ('M4' hole) 229-430mm.

Again, these ARE NOT DEFINITIVE answers. The Barrel/Cylinder volume ratio will depend on your case, and keep in mind is ALSO INFLUENCED BY BB WEIGHT.

I don't know the formula for that, but there is a large influence played by the BB.

But before you stress out, remember that there is no perfect machine in the world. You CANNOT obtain a perfect Cylinder/Barrel match, and after you throw BBs and Compression Leakage and all sorts of other crap in, you end up with a pretty flawed system.

Try to match them up as best you can, and if you know what you're doing, you'll manage.

[Kos-Mos]

Originally Posted by JLiang

The thing is, cylinder type must be changed if your barrel length is changed.

There's a lot of math involved, of which you can go as any senior member (I personally am not going to bore the crap out of everyone with the details). Basically, the volume of the cylinder must match the volume of the barrel in order to achieve maximum results.

Think about it like this. If you have an amount, say, 60 mm cubed worth of air volume in your cylinder. When your piston pushes it out down the barrel, that volume should be enough to get the BB out, and just that. Too much is not good, and too little is not good, either.

We'll use the previous example. If you have a cylinder that has 60 mm cubed of volume, and your barrel has 70 mm cubed of volume, the amount of air in your cylinder has run out before your barrel has. Therefore, the BB becomes 'stuck' in equilibrium. In layman's terms, your BB now has to 'suck' air in order to continue going.

That was an example of a barrel being too long. If a barrel is too short, say, 40 mm cubed of volume (All these numbers are hypothetical, by the way), your 60 mm cubed of cylinder volume is not yet empty by the time the BB has left the barrel. This results in overpressure, and the excess air continue to buffet the BB after it's left the barrel. This results in unstable flight, reducing accuracy, and potentially the life of your gearbox.

GENERALLY, and I repeat, GENERALLY, the pairings of Cylinder Type to Barrel Length should be as follows:

Type 0: (No hole) 450mm+.
Type 1 (Tip hole) 350-450mm.
Type 2 ('M4' hole) 229-430mm.

Again, these ARE NOT DEFINITIVE answers. The Barrel/Cylinder volume ratio will depend on your case, and keep in mind is ALSO INFLUENCED BY BB WEIGHT.

I don't know the formula for that, but there is a large influence played by the BB.

But before you stress out, remember that there is no perfect machine in the world. You CANNOT obtain a perfect Cylinder/Barrel match, and after you throw BBs and Compression Leakage and all sorts of other crap in, you end up with a pretty flawed system.

Try to match them up as best you can, and if you know what you're doing, you'll manage.

Sorry, go back to your maths, it's really basic stuff and you are wrong on both the "matches" and your theories behind the works...

Too "small" cylinder will result in slight FPS drop and important accuracy issues as the BB starts to slow down before leaving the barrel because the air pressure drops. The BB then has less help to push the air in the barrel tip out (it is harder to blow in a straw than out in the air... same thing).

Too "large" cylinder will result is LARGE drop of FPS with no consequence in accuracy. Because the system is spring-driven, the speed of the piston and thus air pressure is not constant. That means that most of the force is transmitted to the BB in the last section of the barrel/piston travel. The BB will then simply have less energy resulting in less FPS. Most people would not see this difference as the FPS drops cuts only 10-15 feet of range. Technically, you can use a stronger spring to get the exact same results as using the correct cylinder. But it will put a lot more stress and wear on the mechbox components.

If you really want to match a barrel and cylinder, you have to measure the volume with water displacement and leave a bit more in the cylinder than barrel. You want the pressurized air to push the barrel out then dissipate in the atmosphere gradually at the tip, once the BB left the barrel.

But a rough estimate:

Over 500mm -- Bore-Up kit, full cylinder
400mm-540mm -- Type 0 (full cylinder, no cut)
340mm-455mm -- Type 1 (hole cut at the tip, opened at the edge)
300mm-380mm -- Type 2 (M4 type, cylinder cut at 3/4)
255mm-325mm -- Type 3 (cut in the center, MP5K/P90)

Some Chinese MP5Ks used Type 2 put backwards. It is not far from the correct volume, so it had very little difference (especially with that short of a barrel).