You either overestimate projectiles or underestimate powered melee fighters. Simple strafing is already enough to complicate aiming with a normal gun - unless you have an iron grip and perfect control over your body, in which case you could easily keep the barrel steady and land the bullets more or less precisely while moving. However, add the decreased projectiles speed as a factor, and the difficulty increases exponentially. One has to take into account the time it will take the bullet to actually the opponent, which at 30 meters - a dangerously close distance - will equal to roughly half a second. Considering that their target would have to move only about 1 meter to avoid being hit, that is a lot of time for a bullet to reach a moving target.
EDIT: hadn't read your second comment before posting this. I worry the same about facing guns in this tournament, however, 250 fps is too low of a speed in my opinion. Also, my point about bullets not able to simply kill on touch still stands true.
EDIT: hadn't read your second comment before posting this. I worry the same about facing guns in this tournament, however, 250 fps is too low of a speed in my opinion. Also, my point about bullets not able to simply kill on touch still stands true.