Below is the reason why the bronze distributor gears are used. This came directly from Summit's website. As I said before, Winze, it's cheaper to change a worn distributor gear, than changing out the camshaft.
Gary
***************The right distributor gear for your roller cam application.
These bronze distributor gears from Mallory are compatible with any cam, and recommended for steel billet mechanical roller tappet cams and slot hard faced steel billet mechanical flat tappet cams. Bronze gears absorb the increased wear in special cams and magnetos, and are easily replaced before costly damage to the camshaft gear occurs. The gears are precision-machined from the highest quality aluminum silicon bronze alloy for maximum durability.