John,
It is indeed either powder and/or lead that is coming back at me, as I can feel particles hit my face, and when I look in the mirror after shooting this gun, I can see small particles on my face and shirt. (Yes, I am using safety glasses.) I have experienced VERY occasional blow back with other revolvers, using certain loads, but nothing like this one does.
As noted above, I recently purchased one of the newly released Ruger SP101 .22lr revolvers, and it shows NO significant leading after shooting hundreds of rounds, and doesn't blow-back powder/lead. Why can't my S&W do the same thing?
I can try some higher velocity rounds in the 617 (CCI Stingers, perhaps?) out of curiosity, but if it won't shoot regular run of the mill bulk .22lr ammo, it's not acceptable to me. It defeats the purpose of having a .22lr.
James