New systems and methods have been invented for explosively forming openings, ledges, windows, holes, and lateral bores through tubulars such as casing, which openings may, in cerain aspects, extend beyond the casing into a formation through which a wellbore extends. In certain aspects openings (e.g. ledges, initial, or completed windows) in wellbore tubulars (e.g. tubing or casing) are made using metal oxidizing systems, water jet systems, or mills with abrasive and / or erosive streams flowing therethrough and / or therefrom.