When you cut a stock to fit someone's length, how do you measure it? I have heard from the shoulder to the trigger finger when bent but that seems to be to many positions and movements to cause a bunch of different readings. What is the best way to do it. My 7.7 Jap has a real short stock and I need to add to it. Is there some kind of adjustable stock you can set to get your length?

I've used a rubber slip on recoil pad and used known shims in it to have folks see if they like a length. Add or remove shims until the guy says.....that's it. All the gages are not worth much if the guy brings the gun to the shoulder and says.....AAAAHHHHHHH....too short/long.
LOP to me is from the trigger to the far end of the stock/butplate/recoil pad.

I fit a few hundred stocks a year for customers. When the gun is being mounted it shouldn't hang up on the arm or shoulder. When mounted your thumb should be not less than 1.5" from your nose so you don't bump yourself. The clothing you will be wearing while using the gun need to be taken into consideration as well. You will also find that different shape pistol grips lead to different LOP's for the same shooter as well. After making the stock fit, then you can position the scope properly. Good shoot'n