A tight barrel will lead to tight shot grouping and greater range ONLY IF barrel pressure is constantly maintained high and the projectile is a tight fit on the barrel.
A loose barrel, commonly seen in nerf guns, has wide shot grouping, is ineffecient in terms of propulsion of projectiles(i will look further into loose barrels)
Nerf Guns are loose barreled because they cannot(Even without air restrictor, or with your semilethal homemade) have a velocity high enough to get darts to effeciently fly past the tight barrel(see my topic on rifling). Military guns (such as the AR-15/M-16, whose springs are exploited by the hardcore nerf gunsmith) on the other hand, are TIGHT barreled because the bullets they fire can effectively use the advantages of a tight barrel, even with the intense friction inside the barrel when firing.
As always, i will conduct more research on this matter in my free time.
Edited by Nerf FNG, 06 November 2013 - 08:55 PM.