What is the Accu-Prime Manual Bench Priming Tool from Lyman? Glad you asked! The Accu-Prime tool is one of the most accurate and precise priming tools available! What makes this tool so accurate is their patented adjustable priming punch! Lyman's patented adjustable priming punch is unique in that the primer cup acts as a stop as it contacts the bottom surface of the cartridge case. In this manner, you can precisely control the exact amount of primer depth below the bottom surface of the case! S