Advanced Bimetallic Liner. Specialized form of ABN. Instead of a single-step, single-material plating, the ABL Plating process is based on a layered approach made possible by two OS-developed hard-nickel alloys. The first alloy is used as the bottom (bonding) layer, to fuse the top layer to the brass liner. The second alloy, developed for superior hardness, forms the top layer. Together, they create a barrier that protects the liner against excessive heat and wear.