Floor Sweep Compound In Tumbler

That would scare me. Especially if you tumble after gas, because the gas might not play well with this material you're asking about.
Tra tor supply has some kind of Cobb grit that they use for chicken cages, if you're having trouble getting Cobb. I'd try that first if I was in a pickle.
Hope this helps.

 

Floor sweeping compound is made of sawdust OR other absorbent fibrous material and usually contain oils, waxes or water-wax emulsions. Other materials that can be present is salt, sand, coloring agents and perfuming agents. Doesn't sound too feather friendly to me.

 

Yikes! Yeah, I don't even know what this stuff is. Not sure why the author would want to get away from Cobb grit other than he cant get it or it is costly where he gets it.

 

Cob grit is the best tumbling medium that I have used. If used properly, it will not stick to the down when dry, it is reusable and not costly.