Found this earlier last week when I was finalizing my research on bullets for my Glocks and handloads:
HARD CAST BULLETS IN POLYGONAL BARRELS
True hard cast bullets (as opposed to lead swaged bullets) that are properly lubed will not lead foul polygonal barrels any more than any other type of rifled barrel. Ever since Glock Corporation warned to not use lead bullets in their pistols with polygonal barrels, a myth that hard cast bullets will lead foul polygonal barrels has become wide spread in some parts of the firearms world. However, the myth is untrue. Hard cast bullets are not "lead" bullets. (See my article on "Dangerous Pure Lead Cowboy Bullets")
Pure lead or nearly pure lead bullets have a tendency to foul any barrel, not just polygonal barrels. Years ago, when several Glock pistols experienced cracked barrels because of fouling build up from shooting pure lead bullets, Glock issued a warning not to shoot lead bullets in their polygonal barrels. From that warning, the myth that you should not shoot hard cast bullets in polygonal barrels was born.
Provided you use real hard cast bullets with good lube, you can shoot them all you like in polygonal barrels without causing lead fouling deposits at the front of your chamber or anywhere else in the barrel. If you are concerned about lead fouling from hard cast bullets, all you have to do is to clean your barrel after firing hard cast bullets and before firing any jacketed bullets. However, in my experience, quality hard cast bullets won't foul a Glock polygonal barrel or any other type of barrel but lead bullets normally will.