Just in case anyone is interested; I successfully fired off 5 black powder rounds through my SKS today.
I took some brass cased surplus, pulled the bullet, dumped the powder and packed the case full of Goex 2F and stuffed the bullet back on.
All the rounds cycled the action; weakly, but nevertheless, they cycled. The bolt even locked back after the final round.
Fouling was not terrible, the bore was still fairly clean; I fired a regular smokeless round afterwards and the bore wasn't significantly cleaner.
If you were on the 50yd range at silverdale this morning, you might have witnessed it; one of the RO's on the 50yd range definitely took an interest.
I'll report back after cleaning and let you guys know if cleaning was any more intensive than usual.
While there's not too many practical applications for running BP in an SKS, it's certainly satisfied my curiosity.
Now I'm curious as to how many rounds can be fired before it stops working.