Millingford barrels are made from a variety of materials, they are also precision honed and are polished within API specified tolerances to give an optimum surface finish. They are straightened to a maximum of 0.005” Total Indicator Reading (TIR), barrels are checked for straightness by drift testing with a 5ft long test plunger with minus 0.0005” to 0.00075” fit. Hardened barrels: Made from low chrome molybdenum alloy steel with a nitride hardened bore to give a surface hardness between 58 and 63 RC. This is our standard barrel with mild to moderate corrosive and abrasive environments. Chrome plated: Base material and chrome plating to customer specifications. For use in mild to moderately corrosive environments but with extremely abrasive conditions. Monel barrels: Made from menel 400 which has excellent corrosion resistance properties for extremely corrosive, but non abrasive materials.