How many external (cm 2 ) are there for the .338 lapua magnum chambering?
CREATE TABLE table_29162 (
    "Chambering" text,
    "P1 diameter (mm)" text,
    "A external (cm 2 )" text,
    "P max ( bar )" real,
    "F bolt ( kgf )" real,
    "F bolt" text
)
SELECT COUNT("A external (cm 2 )") FROM table_29162 WHERE "Chambering" = '.338 Lapua Magnum'
Below are sql tables schemas paired with instruction that describes a task. Using valid SQLite, write a response that appropriately completes the request for the provided tables. ### Instruction: How many external (cm 2 ) are there for the .338 lapua magnum chambering? ### Input: CREATE TABLE table_29162 (
    "Chambering" text,
    "P1 diameter (mm)" text,
    "A external (cm 2 )" text,
    "P max ( bar )" real,
    "F bolt ( kgf )" real,
    "F bolt" text
) ### Response: SELECT COUNT("A external (cm 2 )") FROM table_29162 WHERE "Chambering" = '.338 Lapua Magnum'