Lil Gun burns past peak around 16" with 250 FTX bullets. That's not to say that the remaining but dropping pressure won't still contribute to more velocity. Far exceeds the loss due to bore friction. That's more of an issue with long barreled, 22 BR rimfire barrels. In their case, the main benefit from the longer barrel is it stabilizes the velocity ES, which is real important when you're trying to put a .224 bullet
consistently inside a .375 ring at 50 yards, while having to re-aim every shot and settle down to read the wind,
against the clock.
My other passion Hoot