My .357 Mag barrel has a very long, gradual leade at the end of the chamber, way longer than any other rifle barrel I have been able to see so well (another Handi advantage -- you can look at the chamber a whole lot more easily than a bolt-action allows).
Bluebayou -- The Sinclair measuring device is nothing more than a steel rod with a couple of stops that can be locked with set screws. It just records the depth of the chamber from the bottom of a bullet to the end of the chamber. If you have a caliper with a depth-measuring function, you don't need the Sinclair device for the Handi. You can calculate cartridge overall length by measuring your bullet's length with a caliper, then dropping the bullet nose-first into the chamber until it seats loosely at the origin of the rifling (DON'T press it). Then, use your caliper's depth-measuring function to determine the distance from the base of the bullet to the end of the chamber. Add the two together, and you have the length of a cartridge with that particular bullet touching the lands of the rifling. Reduce the sum by about 0.003" to start and you have a good working cartridge overall length, for use with starting loads. Vary the overall length a thousandth at a time to see what your barrel likes best.
Example: the Honady .357" diameter 180-grain XTP is 0.750" long. From its base in MY chamber to the end of the chamber measures 1.291". Added together that's 2.041", so 2.0" to 2.001" for the loaded round should put the bullet 3 or 4 thousandths off the lands. The OAL figure I have for .357 Maximum is 1.990". Unless the brass jams against the long leade of the rifling, sounds like I have a Max chamber, whether intended by NEF or not. Once again, this is MY barrel, not a standard barrel.
Tim -- If this basement-gunsmith method sounds fishy to you, please let us know before I blow up my gun and someone else tries it and blows up THEIR gun. Thanks!