Don't set the die to set the shoulder back 0.001" or 0.002"...
... first off, you will not be able to accurately measure that - even with the gauges mentioned above.
But secondly, there is no need to size the cases that much, cuz if you set the die up that way, you will be also sizing the body every time, and there is no need to do that, cuz you will be overworking the brass a bunch.
If he doesn't have a "neck size die", have him set the FL die up so it is about 1/2 turn off of the shell holder, and don't touch the shoulders until the cases are tight in the chamber.
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First off, what's so hard about accurately measuring case shoulder setback? If you can read a micrometer, I'd say most anyone can do this very easily, using the inexpensive gauges.
As far as overworking the brass, that minimal setback will not wreck your brass. Most likely, the case necks will fail before you ever stretch the body enough to be a problem.
If you want to neck size, thats fine: use a neck die. However, backing off the full length die will cause the shoulder to rise... and within a few loadings, that brass will get tight in your gun, to the point where it might not chamber. I'd much prefer having things work smoothly, all the time.
Backing off the full length die can be useful to find the correct setting for it though. Take a couple brass, size them with the full length die backed off 1/2 turn, load and fire, then repeat. Usually after the second time, that case gets pretty snug. Then, you can take the full length die down in small increments, until you can just barely feel that sized case being chambered. Your full length die will then size your brass perfectly for that gun. (But the gauges do the same thing, quicker and easier)