Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_29159 ( "Chambering" text, "P1 diameter (mm)" text, "A external (cm 2 )" text, "P max ( bar )" real, "F bolt ( kgf )" real, "F bolt" text )

### Question ###
What is the p1 diameter (mm) when .300 lapua magnum is the chambering?

### Accurate SQL ###

SELECT "P1 diameter (mm)" FROM table_29159 WHERE "Chambering" = '.300 Lapua Magnum'