I will be reloading for several friends ar's 223. Does you just load to the specs noted in the book or do you experiment with each? I don't have one to experiment with.

It happens that people reload for others but it's not a good idea. Civil liability is the problem if ANYTHING goes wrong. If you must, have them present EVERY time you load for them. Teach them and have them reload their own.

Yep!

And depends on your actual question. If the headspace is similar on each of them, maybe within 0.002", probably fine using the same sizing die setting. Otherwise, I'd personally adjust it for each - or get some shims to make the adjustment, much easier (set for the shortest headspace and use the shims to go longer). Just my personal opinion, nothing else.

And most likely setting OAL to fit the magazine, so same from rifle to rifle.

chamber size can vary and for brass life, you size to each chamber...

Accuracy can vary from gun to gun too some. Depends on how picky you are.

RE liability, its always tehre, bothers me none. The folks I load for would not be ones to sue.... YMMV

I don't and won't load for other people