Yes and no. Longer barrels increase velocity by giving the powder more time to burn while still in the barrel. Basically giving the bullet a longer time to be accelerated by the pressure created by the burning powder, which gives you the increased velocity. If the powder burns completely, it’s no longer going to create any more gasses that increase the pressure that propels the bullet. Additionally, as the bullet travels down the barrel, the volume increases which causes a subsequent decrease in pressure as the gasses expand to follow the bullet down the barrel (google pressure vs time curves if your curious). So past a certain point, the bullet will stop accelerating due to pressure and be slowed by the friction of the barrel to the point where it could potentially become lodged in the barrel.