The problem with polygonal barrels comes with use of non-jacketed ammo (lead bullets). Use of jacketed open-tip bullets should be no problem. I have heard some people using lead bullets succesfully in polygonal rifled barrels, but that requires very careful cleaning of the barrel, regularly and often. If you have to ask about it don't try it. Better leave experimenting to experts and just follow the common rule of no lead bullets (wadcutters, semiwadcutters) with polygonal rifled barrels.
Ossi