Abstract: Method and apparatus for perforating a well casing (14) with a large pressure differential toward the well casing (14) from the surrounding oil and gas-bearing strata using a casing gun attached on a wireline below the tubing is disclosed. A perforator (12) is attached to a casing gun adapter (10), the casing gun adapter (10) is releasably attached to production tubing (16) and inserted into the well casing (14). After the production tubing (16) is installed, a collar locator (26) and a firing mechanism (44) are run on a wireline and attached to the casing gun adapter (10). The casing gun adapter (10) and the perforator (12) are released from the tubing and lowered to a predetermined stratum using a collar locator where the perforator (12) is detonated. After detonation, the perforator (12) and casing gun adapter (10) are raised and secured in the production tubing (16). The collar locator (26) and the firing mechanism (44) are detached from the casing gun adapter (10).