Reballs themselves aren't problematic, the dirt and grime that usually gets on them is what causes problems. I would use a barrel you don't care about because dirty reballs can act like sandpaper down your barrel and breech but I wouldn't worry too much about actually breaking your gun shooting reballs. I put probably 5+ cases through my Marq 6 with reballs at a local reball field and it didn't have any obscene amounts of wear in the breech or barrel. The bolt would get pretty dirty though so be sure to clean your gun after you use it.
This line is in remembrance of Jared Wilson, friend and paintball teammate who died on 7/27/2005. My Old Feedback +1/-0 | CCM T2 | OLED G6R | Entertaining Offers for either/both