Inner barrel length
Work out your barrel volume and the air your cylinder needs, and check the usual lengths per replica.
Your barrel
Result
- Barrel volume
- 10,366 mm³
- Recommended cylinder air
- 15,550 – 25,916 mm³
- Nearest standard lengths
- 363 mm · 407 mm
Usual lengths per replica
| Replica | Inner barrel |
|---|---|
| M4 / AR15 carbine | 363 – 370 mm |
| SCAR-L standard | 363 – 384 mm |
| SCAR-L CQC | 275 mm |
| SR25 / AR10 | 455 – 510 mm |
| P90 | 247 mm |
| MP5 (A4/A5) | 208 – 229 mm |
Indicative only: every brand and version differs, and many lists mix outer and inner barrels. Always measure yours before buying.
Standard lengths
| Length | Volume | Cylinder air |
|---|---|---|
| 110 mm | 3,141 mm³ | 4,712 – 7,853 |
| 141 mm | 4,027 mm³ | 6,040 – 10,067 |
| 229 mm | 6,540 mm³ | 9,810 – 16,349 |
| 247 mm | 7,054 mm³ | 10,581 – 17,634 |
| 275 mm | 7,853 mm³ | 11,780 – 19,633 |
| 300 mm | 8,567 mm³ | 12,851 – 21,418 |
| 363 mm | 10,366 mm³ | 15,550 – 25,916 |
| 407 mm | 11,623 mm³ | 17,435 – 29,058 |
| 455 mm | 12,994 mm³ | 19,491 – 32,484 |
| 509 mm | 14,536 mm³ | 21,804 – 36,340 |
| 590 mm | 16,849 mm³ | 25,274 – 42,123 |
Why it matters
The cylinder has to push an air volume proportional to the barrel's: 1.5 to 2.5 times is the usual range. With less air you get suction (the BB slows before leaving); with much more, the extra air adds nothing and stresses the gearbox.
That is why switching to a longer or shorter barrel usually means checking the cylinder type (full or ported). For the full calculation with your cylinder, use the ratio calculator.
Frequently asked questions
What inner barrel does an M4 use?
Most M4 carbine AEGs use an inner barrel of about 363 mm (some brands, 370 mm). CQB versions are shorter.
Does a longer barrel give more range?
Not necessarily. Beyond what the cylinder can fill, you lose speed. Range depends more on the hop-up, the bucking and the BB weight than on length.
Which inner diameter should I choose?
6.03 mm is standard; precision barrels (6.01-6.05 mm) slightly change air use and consistency. The calculator accepts any diameter.