Good job!
BTW it's not slag that's coming off the pellets, it's lead. Slag is a bi-product of smelting and was removed from things long before JSB ran that lead through the machines
IME the thing about washing that improves things is getting rid of those little bits of lead that are loose but stuck to the pellet. Those little bits can easily get stuck in the barrel. Anybody that's run a tight patch through their barrel will see the little bits on the patch. I can speculate on how exactly that effects POI, but I'll leave that...
A couple things I do differently...
I use hot water, as hot as I can stand to work in. The hotter the better. I'm assuming the coating on JSB pellets is oil based and oils come off better/faster with heat. I use the Dawn too, great stuff!
I use shop towels to take up the excess water, then use several old baking sheets I picked up from a yard sale to lay them out to dry. Not being stacked on top of each other helps them dry faster.
I don't wash as a first step, for me I feel I save time by doing a high level visual inspection, then run it through my sizer. I will often toss pellets in the sizing step, it becomes very obvious with experience that a pellet is over/under sized just by dropping the pellet in the sizer. I toss anything that doesn't "look the same" in the sizer. Another reason I size before I wash is that sizing can/will create those little bits of lead.
After washing I do a more detailed visual inspection under 20x magnification and high light. Pick off any little bits that might have survived washing. Toss for various reasons like dents in the head, symmetry and the like.
Then its time to sort by weight. This is so subjective! What works for me, my guns and what I'm expecting of them is going to be different than someone else. But IME you will get a lot of one small range size, something like 85%+ in one small range of weights. In my testing this will also be the "sweet spot" and these will shoot more consistently than say the outer edges of the bell curve of weights. Anymore I will only shoot this center weight grouping for score.
I plan to testing out coating pellets later this year. My assumption is that coating will accomplish a couple of beneficial things... First that it will prevent lead from coming off the pellet while going down the barrel potentially resulting in a degraded accuracy. Second that the coating will fill many of the little imperfections in the head of the pellet resulting in a mirror smooth surface. Remember our pellets are plowing through the air with the head and any little dent is going to effect the stability/flight path of the pellet.
