The Lock-N-Load Headspace Comparator extends brass life, improves accuracy, and enhances safety. The gauge measures variations in brass before and after firing or re-sizing. It allows for headspace comparison between fire-formed brass and re-sized brass. The five bushings that come with the Lock-N-Load Headspace Comparator provide the ability to check most bottleneck cases, from .17 Rem through belted magnums. Ackley Improved chambers use the same bushing size as the parent case.