If you dont have a stoney point gauge then you can take a bullet and put it in a case just enough for it to hold, color all of the bullet that isnt in the case and push the cartridge into the chamber, pull it out and if the bullet is stuck just take a peice of a cleaning rod and drop it down the barrel, re-seat the bullet to the mark the case left on the bullet when it got pushed into the case and measure the length. This usually gets your OAL length from the ogive. I sometimes do this because I dont have a OAL gauge. I usually just trim the cases to an exact length and maybe .004" shorter on accident, then I'll seat the bullet to the same length as a factory load of the same bullet weight then due to each bullet being longer or shorter I'll re set my seater die to compensate for each bullets length. That way each cartridge is the exact same length.