Inner Barrels

Bore size: how tight is too tight?

Stock inner barrels are around 6.08 mm; a tight-bore barrel of 6.03 or 6.05 mm reduces the gap around the BB, raises efficiency and gives a small gain in velocity and consistency. A 6.01 or 6.02 mm bore is the tightest choice and demands clean, high-grade BBs, since any dirt or an oversized ball will jam. For most AEGs and gas pistols 6.03 mm is the sweet spot; snipers who sort their BBs go tighter. Stainless steel resists wear and corrosion, brass is cheap and easy to polish, aluminium is light.

Length and cylinder matching

Longer is not always better. A barrel should match the air volume of the cylinder in an AEG, which is why a 363 mm barrel suits a full cylinder and a 247 mm barrel a ported one; a longer barrel in a short gun can actually lose velocity. Measure your outer barrel, or hide extra length under a suppressor. Pistol barrels run 90 to 120 mm, carbines 230 to 370 mm, rifles up to 510 mm and sniper rifles longer still. The length and bore filters do the sorting.

Fitting

An inner barrel is only as good as its hop-up: fit a new bucking at the same time, check the window cut matches your chamber type (AEG, GBB, VSR-10 or L96) and clean it with a cleaning rod before the first shot. Barrels are unrestricted parts.