Regulating 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.
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.