The Hornady Lock-N-Load OAL Gauge (formerly Stoney Point) is an extremely easy to use tool. It only takes a couple of minutes to find the overall length for a particular bullet. The tool is threaded on one end to accept specially modified cartridge cases. Once threaded onto the tool, a bullet is inserted into the cartridge. The tool is then inserted into the chamber of your rifle. The push rod on the tool is used to push the bullet up against the rifling. The rod is then locked in place and the tool can be removed from the rifle. You then measure across the base of the cartridge and the top of the bullet with your dial calipers (use of a bullet comparator at this time is highly recommende Mfg: Hornady SPECS: Gauge- Machined aluminum, 12" (30cm) long, anodized finish, red. Straight Gauge for bolt and single shot actions. Curved Gauge for auto, pump, and lever actions.