Tightbore Barrel

Stock inner barrels typically run around 6.08–6.05mm bore; tightbore aftermarket barrels tighten that to 6.03mm or below, which cuts the space a BB can wobble in as it travels and lets the bucking's nub grip it more evenly for consistent backspin.

The tighter the bore, the pickier the barrel gets about BB quality — undersized or poorly finished BBs jam or scuff more easily in a very tight bore than a stock one. Tightbores are the default choice on DMR and precision builds, where the accuracy gain outweighs the need for higher-grade ammunition.

Cleaning frequency matters more with a tightbore than a stock barrel, since even a thin film of residue narrows an already tight bore enough to start scuffing BBs or causing intermittent hop-up inconsistency.