Which material is commonly used in the practice of fire lapping?

The practice of fire lapping involves using a specific abrasive material to improve the accuracy and smoothness of a firearm's bore. Aluminum-oxide grit is commonly used for this purpose due to its effectiveness as a non-toxic abrasive that can help polish the barrel.

Aluminum oxide is hard, durable, and can create a finer finish than many other materials. When used in fire lapping, it helps to smooth out imperfections in the barrel's surface, which can enhance bullet travel and thereby improve accuracy. The grit effectively removes any minor burrs or rough spots that might have formed during the manufacturing process.

Other materials, such as steel shavings, lead dust, and copper particles, are not typically utilized for this specific process. Steel shavings might cause more damage than benefit due to their hardness, while lead dust and copper particles do not provide the same level of abrasive action needed for the lapping process. Thus, aluminum-oxide grit is the preferred choice for fire lapping.