Re: How long do you expect accuracy to remain
If this were a benchrest gun shootin in the zeros (0.0xx) for 5 shot groups, you might get 6-8 shots before groups began to open up visibly and statisctically.
If this were a simple hunting gun shooting top-line hunting ammo and shoots 1.2" 5-shot groups, you could probably go thousands of rounds befor you could measure the fouling hurting the accuracy.
So, more data is needed to answer your question.