Lock-N-Load O.A.L Gauge The Hornady Lock-N-Load O.A.L gauge regulates seating depth and the resulting “jump” to the rifling is widely regarded as fundamental to improved accuracy. A few thousandths of an inch change between the bullet and the rifling can make the difference between average accuracy and real tack-driver performance. Lock-N-Load O.A.L Gauge CURVED MODEL Item #C1550 For all autoloader, lever-action, or pump-action rifles. Also fits all bolt-action and single-shot firearms. Inserts into chamber through ejection port. Not compatible with Adapter “D” or short-bodied cases. Achieve precise bullet seating depth. To use the Lock-N-Load® O.A.L. Gauge, you will need a Modified Case (sold separately) to fit your firearm’s chamber and thread it onto the gauge. These specially prepared modified cases are threaded at the case-head and have a .002″ oversized neck to accept the same bullets you intend to load. This is critical, as the Lock-N-Load® O.A.L. Gauge dimensions obtained will be accurate to .001″. These results cannot be attained with competitive products, which use a simulated bullet with an arbitrary shape.   Lock-N-Load® O.A.L. Gauges & Modified Cases – Hornady Manufacturing, Inc J&A Outdoors – Firearm Solutions – Shooting Products (jaoutdoors.com)