Check the listing for details. Sinclair International - Bullet Comparator Insert SS - .308/7.62MM Caliber. Condition: New. Listed at 9.99 USD. Photo for reference only Our Sinclair Bullet Comparator attaches to the blade of your caliper and uses inserts for each specific caliber. The inserts are stainless steel and machined with a taper and a short straight section to more accurately duplicate the chamber throat. This eliminates the wobble experienced with many comparators which have standard drilled holes. Our design allows you to quickly and accurately measure the bullet's bearing surface of the bullet. Comparator inserts are available in 17 thru 45 caliber, and they can be used in both the Sinclair and older Stoney Point comparator bodies. These inserts are not intended to measure rounds seated to magazine length or shorter. Comparator Body sold separately and calipers are sold separately.