Also allows for better air efficiency. When it comes to an air gun, the longer the barrel, the higher the rate a projectile increases to.
For instance, with a 10 foot barrel a paintball could increase to 500mph or more. Physics son.
Plus I had a friend who did his engineering final on the difference between barrel lengths and accuracy. Showed that as a barrel gets longer it does get more accurate.
Used a wind tunnel and a mounting block as well as the same bag of paint on all tests.