A couple thoughts.....
I've actually had one of these markers for about a year and a half....and here's a few things to consider. If your buddy is using old/paint left out in the heat/brittle paint, this marker will chop it to pieces. The gti+rampage operates at about 850 psi and therefore puts a lot of pressure on the paintball when air is discharged by the bolt. Basically, if there's anything even remotely wrong with the paint that's being used, this gun will shred it. Even if there's not anything wrong with the paint, the operating pressure of the gun is so high that breaking paint is just something he may have to learn to live with.
I've had the exact issue you describe, and this may help alleviate the problem. Unscrew the eyes from the body of the marker and remove the little black eye casings and reinstall the eyes. The black casings are meant to hold the eyes in the place, but they end up causing more trouble than anything, plus they stay in place without them. The eyes tend to recognize the casing as a paintball because they cover up most of the eye, so the marker still fires even if no paintball is in the breach, which will cause the marker to shred paint like crazy. This is more of a theory than anything, but removing the casings has allowed the marker's eyes to function properly.
Third.....if he's adjusted ANYTHING on the circuit board besides the BPS or debounce-- it will screw up the performance of the marker so bad it's practically unusable. DO NOT change the dwell. He can set the debounce to around 8-9 and be safe and the BPS to around 15. The eyes are not good enough for the marker to actually fire 25 bps, as the manufacturer claims. If he starts changing the circuit board, the marker will do crazy things on the field, including shooting 4 balls at a time, not shooting at all, shooting at 100 fps, the solenoid not activating, etc. It's a disaster. The rampage board is pretty awesome, but it's too advanced for the Piranha--don't adjust the settings as if it were an Angel or a Luxe.