Rust is not "dirt, grit, oil or grease" so that rusty shot does not contravene the quoted specification. This implies that you could be forced to accept the shot, having purchased it. On the other hand it should not have been rusty. Steel shot as-manufactured is covered with a thin skin of iron oxide. Reputable manufacturers store their shot in air-tight containers to prevent water molecules in damp air reacting with the iron oxide to form hydrated iron oxide, aka rust. I suggest that you do not use the rusty shot but ask your supplier to replace it with rust-free shot.
