Ok lets do this in parts
) Cleaned cases, deprimed, cleaned inside of neck with a nylon brush{} Yes!!!!
2) Lubed case with my standard case lube, bumped shoulder [and used a bushing that would resize the neck to give about 0.003" neck tension}<<< cut this part out
3) Cleaned cases to remove case lube Yes!!!!
4) Lubed inside case neck with graphite Yes!!!!! very little is required a dusting inside case mouth
5) Resized the neck with an expander mandrel give 0.002" neck tension Yes!!!!
6) Relube the neck<<<<<<< NO cut this part out the graphite in the neck already from neck tension is all you need} and seat bullets to 0.020 from the lands (didn't have time to do the seating depth ladder - so I crossed my fingers and went with 0.020) that is OK
So yes your barrel is going to speed up between rounds 10 and 200 this will change your SD, you are using Retumbo right? so heat should not change the speed or sd as it is a extreme powder, and yes upon firing quickly lay another round on top of Mag and be prepared to fire when your spotter gives you correction or you yell hell yeah when he says impact.... but be ready to send another round to take advantage of wind condition.
Yes numbers will drop and rise a small bit due to first firing brass and case stretch and as you reach copper equilibrium you will see your numbers start to settle that is why I hardly ever clean my gun only when accuracy starts to fade, also what seating die are you using are you getting consistant size? measured from the ogive NOT overall length .
your 6 and 7 strings are shooting almost exactly like my gun playing with seating depth and tweeking powder charge up or down will also help, the biggest thing that helped my SD was being meticulas on weighing my powder charges no throwing from scale I weigh each one with a digital scale after getting charge from powder measure and i trickle up to weight, and stap as soon as my digital scale shows my weight.... but hey you are looking good and on the right track...
And I do nothing on first firing except set neck tension just fire form the case and look for dents etc.