Question: How many  external (cm 2 ) are there for the .338 lapua magnum chambering?
Schema: create table table_26967904_2 (a_external__cm_2__ varchar, chambering varchar, PRIMARY KEY (a_external__cm_2__))
SQL: select count(a_external__cm_2__) from table_26967904_2 where chambering = ".338 lapua magnum"