I would be wary of any polystyrene filler/buffer. The range of formulations of polymers is vast and somewhat unpredictable. Any polymer getting rammed down a barrel by incandescent gas has the potential to either burn or melt. Burning can cause residue problems, and melted leftovers in the bore present obvious problems. Shotgun wads are polyethylene formulations, generally more resistant to burning, vaporizing, melting or otherwise causing trouble, but they still can leave melt deposits in a bore if not cleaned. Ethylene or styrene polymers are generally not soluble in the solvent that work for powder like Hoppes No. 9. I've never used it, but I read all the time about corn meal used as a filler. Makes sense as the cellulose (nature's polymer) lights off and burns more readily than manmade stuff without melting.