[PzGren]

I have had excellent results with rust blueing. It is extremely labour intensive, preparation has to be *clean clean* but Midway sells the smallest bottle for about $7. It is not very hard to do, the first job turned brown but now I have a black that can barely be rivaled by hot blue.

I usually use Belgian blue and the biggest downside is that the parts have to be boiled, i.e. you'll need a pan large enough to immerse the part. Kind of hard for rifle barrels.