The inner barrel guides the BB out of the rifle. Bore diameter and surface finish determine how accurately the BB exits — the second most important component after the hop rubber.

An airsoft inner barrel is a thin metal tube that the BB travels through after leaving the hop unit. Its job is simple: guide the BB straight, with minimal contact along its length, and let the hop-applied backspin develop into the airborne trajectory. Two specs matter: bore diameter (typically 6.01mm to 6.04mm internal) and surface finish (mirror-polished or precision-honed). Length is a third spec but it's usually dictated by the rifle's outer barrel rather than chosen for performance.

Bore diameter is the biggest decision. 6.03mm tightbore is the modern consensus sweet spot — tight enough for consistent BB-to-bore relationships, loose enough to tolerate small BB diameter variations across batches. 6.01mm precision tightbore is the tournament-grade option — maximum accuracy with premium BBs but intolerant of any BB diameter variation. 6.05mm wide bore is the older stock standard — tolerates anything, less accurate. Use a tighter bore with consistent premium BBs (BLS, Vorsk Precision, RZR) for the best results.

Brands. Maple Leaf dominates the airsoft inner barrel market with 6.02 and 6.04 tightbores in every standard length. Prometheus is the premium tier — precision-machined, mirror-polished, the tournament barrel for VSR-10 and high-end M4 builds. PDI specialises in sniper-rifle barrels with extreme precision. ZCI and SHS cover the value end. Match the barrel length to your outer barrel length — an inner barrel can be longer than the outer (with a suppressor housing the extra length) but never shorter without specific configuration.

💡 Titan Forge tip: A 6.03mm inner barrel from Maple Leaf with premium 0.28g BBs (BLS or Vorsk Precision) outperforms a stock 6.05mm barrel by a noticeable margin at 30+ metres. The upgrade combo is about £30 of parts and represents one of the biggest accuracy improvements you can make to a stock AEG short of replacing the hop chamber.