The guage shown above is a copy of the Sinclair Seating Depth Tool. $28.95 WITH the bore guide. www.sinclairintl.com
part # 09-400
Only the one above does not show it coming with a bore guide.
Also are you asking for OAL or seating depth which are two different things?
Measuring simple OAL, any dial caliper will work.
IF you want to measure how far the ogive is off the lands to set up accurate seating depths, you will need the sinclair tool above and the Stoney Point Chamber All Bullet Comparator from sinclair part # BC-4000 for all calibers at $27.50 or the Davidson Seating Depth Checker part (two part, base and nose piecer per caliber for $25). It measures the ogive which is the part of the bullet touching the lands.