As promised, I went out and picked up some Reball (reusable) paintballs to try in my Tacamo T68 AK47 styled paintball rifle. I wanted to see what kind of damage they could inflict on various targets. The purpose of the Reball is mainly for practice or training use with paintball guns, they are also used in some indoor paintball facilities. Reballs have the advantage of not only being reusable but also not making a lot of mess.
Another benefit is that Reballs do not break apart and so they will deliver more energy on target which may be useful in a self defense situation with a high fps Paintball gun. Now I am not recommending these guns in any ways to be used for self defense or non-lethal use but other people have suggested it to me, and I wanted to see what these little rubber balls could do to different targets.
Keep in mind I was not looking for penetration as that is not the purpose of a "traumatic round", such as a rubber bullet. Rubber bullets are not supposed to penetrate but rather stun a person.
I found the Rubber Reball Paintballs to be about the same weight as standard paintballs and so they shoot about the same fps which in my gun was about 350 fps.
In conclusion, I would not want to be shot with a Reball out of a high fps paintball gun, as for stopping an intruder, maybe? You most certainly would be able to pick them out of a police lineup because they would be riddled with red welts :)