CREATE TABLE table_26967904_2 (p1_diameter__mm_ VARCHAR, chambering VARCHAR)

What is the p1 diameter (mm) when .300 lapua magnum is the chambering?
SELECT p1_diameter__mm_ FROM table_26967904_2 WHERE chambering = ".300 Lapua Magnum"
SELECT "p1_diameter__mm_" FROM "table_26967904_2" WHERE ".300 Lapua Magnum" = "chambering"