For years I used a piece of 1/4" wooden dowel, a sharp pencil and a set of calipers to measure distance to the lands. Close the bolt on the rifle with empty chamber, drop the dowel down and make a mark at the muzzle. Next, drop your bullet (not loaded ammo!) in the chamber and ensure it's seated using a pencil. You have to hold the bullet in place. Next, put the dowel in the barrel against the bullet tip and make a second mark. Measure between the two and that is the max overall length for that bullet.
Obviously there are lots of ways to make errors using this method. Like most things in life, attention to detail will help yield consistent results.
I will say that I bought a sinclair tool several years ago to do these measurements and it works pretty well. Does it the same way and from the breech. But I got by using the dowel for many years and for hunting rifles, it worked fine.
