Get your AEG’s internals working together. Enter your inner barrel length, bore and cylinder to check the cylinder-to-barrel volume ratio, see which cylinder suits your barrel, and get a hop-up rubber and BB weight to match your power.
Why the cylinder and barrel need to match
When an AEG fires, the piston pushes a set volume of air out of the cylinder. That air has to push the BB the full length of the inner barrel. If the barrel holds more air than the cylinder can supply, the BB slows down before it leaves (under-volumed). If the cylinder supplies far more than the barrel needs, the extra air is wasted and the gearbox works harder than it has to (over-volumed).
Ported cylinders have a hole partway along so only part of the piston’s stroke compresses air, which is how makers match a standard gearbox to shorter barrels.
Which cylinder for which barrel length
| Cylinder | Approx. volume | Suits barrels of about |
|---|---|---|
| Full (no port) | 19.0 cc | 370 to 550 mm |
| 3/4 ported | 14.5 cc | 280 to 420 mm |
| 2/3 ported | 12.7 cc | 250 to 370 mm |
| 1/2 ported | 9.5 cc | 180 to 280 mm |
| Platform | Typical inner barrel | Suggested cylinder |
|---|---|---|
| MP5 / short SMG | 229 mm | 1/2 ported |
| M4 CQB / G36C | 247 mm | 1/2 ported |
| G36K / short carbine | 300 mm | 2/3 ported |
| M4 carbine | 363 mm | 3/4 ported |
| AK47 / AK74 | 455 mm | Full (no port) |
| M16 / SR-25 | 509 mm | Full (no port) |
Hop-up rubber hardness
The hop-up rubber (bucking) puts backspin on the BB so it flies flat for longer. Its hardness needs to suit your gun’s power: a soft rubber grips well at low power, but a powerful gun or heavy BB can squash it and over-hop.
| Power on 0.20g | Rubber | Typical guns |
|---|---|---|
| Up to 330 fps | 60° (soft) | Indoor and CQB AEGs, pistols |
| 330 to 380 fps | 70° (medium) | Most outdoor AEGs |
| 380 to 450 fps | 75° (hard) | Upgraded rifles and DMRs |
| Over 450 fps | 80° (very hard) | Bolt-action snipers |
Our step-by-step hop-up guide shows how to set it once it’s fitted.
Tight bore or standard bore?
| Tight bore (6.01 to 6.03mm) | Standard bore (6.05 to 6.10mm) | |
|---|---|---|
| Efficiency | Slightly higher fps from the same spring | Slightly lower |
| Consistency | Very good with quality BBs | Good |
| BB quality needed | High: seamless, polished BBs | Tolerates cheaper BBs |
| Cleaning | Regularly, or it loses accuracy | Less often |
| Jam risk | Higher with dirty or oversized BBs | Lower |
Watch your fps. A tight-bore barrel or a better air seal can push your gun over your site’s limit with the same spring. Chrono after every change, and check it with the fps to joules calculator.
Planning a spring change too? See the typical fps for each rating with the Airsoft Spring FPS Calculator, and pick a BB weight with the Airsoft Range & BB Weight Calculator.
Frequently asked questions
What inner barrel length is best for an AEG?
There’s no single best length. What matters is matching the barrel to your cylinder volume. Short barrels (around 200 to 300mm) suit ported cylinders, while long barrels (450mm and up) need a full cylinder. A longer barrel doesn’t add range on its own: hop-up, air seal and BB quality matter far more.
What is the cylinder-to-barrel ratio?
It’s the air volume the piston pushes out of the cylinder compared with the volume inside the inner barrel. A commonly used guide for AEGs is about 1.2 to 1.8 to 1. Too little air and the BB slows before it leaves the barrel; too much and the extra air is wasted. The calculator above works it out for your set-up.
Is a tight-bore barrel worth it?
A tight bore (around 6.01 to 6.03mm) can add a little fps and consistency because less air escapes around the BB. The trade-off is that it needs quality, seamless BBs and regular cleaning, or it can jam and lose accuracy. For most players a 6.03 to 6.05mm barrel is a good balance.
Which hop-up rubber hardness should I use?
Match it to your power. Soft rubbers (around 60°) suit lower-powered guns and light BBs, 70° suits most AEGs at around 350 fps, and harder rubbers (75° to 80°) suit DMRs, snipers and heavy BBs. Too soft and a powerful gun over-hops; too hard and a low-powered gun can’t lift the BB. See our hop-up guide.
Does a longer barrel give more range?
Not by itself. Once the cylinder’s air is used up, extra barrel length just adds friction. Range comes from a good hop-up, a consistent air seal, the right BB weight and your gun’s energy. Our Airsoft Range & BB Weight Calculator estimates range for your power.
Upgrade the outside too
Sights, rails, grips, suppressors and tracer units for your build.
More airsoft tools
Airsoft Range & BB Weight Calculator
Find the best BB weight for your gun’s power and how far it should reach with a good hop-up.
Open the calculator →Airsoft Spring FPS Calculator
See the typical fps an M90 to M190 spring gives in an AEG or sniper, and which spring hits your site limit.
Open the calculator →BB Weight FPS Calculator
Chrono’d on 0.20g? See what your gun shoots with 0.25g, 0.28g, 0.30g and heavier BBs.
Open the calculator →A guide based on commonly used figures. If in doubt, ask an airsoft tech before changing internals.