i doubt it is "powder". i suspect you are being sprayed with gasses and particulates (that are already inside your receiver).

all kalashnikovs outgas thru the action cover button hole in the rear of the action cover. just like the ar, this vent can be sealed off by using silicone applied to the button prior to reassembly.

i've also had some success by slipping a o-ring over the button, then installing the action cover.

my reading comprehension must have sucked this morning...fore HAND , not foreHEAD! doh!!!

here's another tip or two:

for slow fire/target plinking: wear a glove for your forehand. no. 1, this will help your accuracy if you are punching holes in paper. all target/match shooters use a glove or mit. no. 2, your grip on the forend should be loose for accuracy shooting. just let the rifle lay in your hand. do not attempt to grasp it with your fingers.

for rapid fire/full auto fun: wear a work glove. it protects the hand against heat, also.

note to self: drink more coffee before logging on!