Springfield Inc. bolt replaced with USGI bolt

My question is if you find a USGI bolt that headspaces to spec. with the headspace guages do you have to check anything else. I will also do the tilt test to see if everything moves on its own without the op rod spring and guide.

I hear about lapping bolts, when and why would you do this?

How do you know if you have even contact on the bolt lugs?

I am going to buy a bolt and check it and if all is good use it or save it for when I need a new barrel and have it headspaced with the new barrel if I ever get that far.

thank for the help and info