The Sinclair Seating Depth Tool has been used for decades by handloaders seeking the most accuracy out of their rifles. We have recently improved our seating depth tool to accommodate 17 and 20 caliber shooters without having to have two tools. Our newest model is made from one fourth inch ground and polished stainless steel with one end turned down for use with 17 and 20 caliber rifles and the other end used for 22 caliber and up. This tool helps you determine the length of a loaded round touching the rifling. This length is generally considered to be the best starting point in load development and the best length for fireforming most cases.
The Sinclair Seating Depth Tool will work with most bolt action, single shot and AR type rifles. The tool includes a Delrin action guide for most bolt-action rifles (Remingtons, Savages, Winchesters, and Rugers), a stainless steel measuring shaft, two stainless steel stop collars and complete illustrated instructions.
We also make a guide for use in AR-15's, AR-10's, and Tubb's 2000's. Many shooters load single shot rounds longer than magazine length. The guide is a little different than our standard bolt-action guides. This guide inserts into the back of the upper receiver (with the bolt removed). The tool is then used as normal.
Big Book Catalog, Issue:68, Page:531
Sinclair, Issue:5B, Page:025