So you expect someone to just "happen" to bring a paintball gun and paintballs to your show? Where I'm from people don't just carry these things around with them all the time. I mean it's not like borrowing a coin or something. In other words, borrowing the item is not natural. People will see him as a stooge.
The borrowed gun method also means that the spectator cannot load the gun himself. He can't confirm that the ball actually went into the chamber just seconds before he fired the gun. In all, the effect becomes much weaker.
This also means you have to give the gun and paintballs back at the end of the performance. So now, you run the risk of an audience member grabbing the gun and firing it at you while you are still on stage. Why not? You caught the bullet before didn't you?
the place that i'm performing at has paintball guns right there and i know the guy that runs them and he said i could use one for this trick.
The risk still remains!! Performing at a place with paintball guns is irrelevant. What is relevant, is the fact the guns are not in your control. Other people have access to them. This means that if you performed the stunt successfully once, somebody could immediately fire another paintball gun at you. You would more than likely fail to catch a second paintball, as the element of surprise is now working against you.
"Velocity" is a showcase effect. As such, the weapon is under your control at all times. Safety concerns are all built into the effect.
Trust me, I would not perform the effect you are describing. The variables and risks are far too great.