The throat diameter range for achieving maximum accuracy is extremely narrow, at 0.004 inches. Deviating from this range, either smaller or larger, will result in reduced accuracy. By inserting the plug gauge into the barrel throat, users can quickly determine when they are nearing the correct diameter, providing a warning before exceeding the optimal range. This tool is also valuable for diagnosing firearms with accuracy issues, particularly those with chamfers cut using our tools, as it may not provide accurate readings on firearms with different chamfer angles. Each gauge is self-piloted, precision-ground, hardened and stepped to indicate both the minimum and maximum optimal diameters. The 11 degree and 18 degree gauges measure both chamfer angles.