You don't need a $50 device to measure the OAL..a long wood dowell will do it fine...put a bullet (a bullet only) in the lands very lightly snug...stick the dowl down the bore from the front and mark the at the crown with a marks alot. then remove the bullet put the bolt in and close it then put the dowl rod back in to meet the bolt face and again mark the dowl at th crown..measure between the two marks and that is your overal max length..take off a couple of thosands and to to the range..you may need to tweek that distance a few thou to get your best accuracy..
I wouldn't go to the trouble except for that holy grail of a group for pictures on the internet!
just load up a good load and sight it in, hope for a 1" group and get there with a proper powder charge and bullet..its a lot easier.
