I noticed clip-on brackets from WW's in your skimmed 'dross'. Skimming off what comes to the top of a WW mix after melting will still leave you with alloyed lead, somewhat harder than pure lead. It would most certainly be nice if simply skimming WW alloy would leave you with pure lead. Not going to happen.
I've tested this myself, back in the 70's & 80's when I had difficulty getting pure lead, but buckets of WW were simply available for the asking at tire shops.
Melting, skimming- let it harden, melting, skimming, let it harden, melting skimming - even 3 times still left me with alloyed lead suitable for my .44 mag. That is, lead that was alloyed and not dead soft. It was softer than before I started, but still considerably harder than pure, dead-soft lead. Yes I know, what I am calling pure lead is likely only 98.6%(Plumbers lead = PB) or 99.0% pure. That is still not 'perfectly' pure, but certainly softer than the result of attempting to soften WW alloy by skimming.
Of course, this harder lead is still usable, but normally with smaller sized balls and patch that will still go to the bottom of the grooves to seal.
Getting a good seal at higher pressure is likely impossible due to the harder lead not forming into the lands as well as necessary.
Using a wad can help in this instance. Be sure to check for accuracy changes.