Well, plastic explosives aren't what you would call conventional. Until a precisely timed triple frequency charge is sent through them by the detonator which is nothing but a small charger and receiver, they're just a hunk of material. You can even burn plastic explosive without setting it off. So I don't think it would fall under the active materials that are scannable category.
And decently sized. For a concussive charge like that, at least 2 pounds total, shaped into fist sized charges.
And decently sized. For a concussive charge like that, at least 2 pounds total, shaped into fist sized charges.