CREATE TABLE table_20821 ("Gun" TEXT, "m/v ft/s" FLOAT, "Shell  ( lb ) " TEXT, "Time to ft  ( m )  at 25\\u00b0  ( seconds ) " TEXT, "Time to ft  ( m )  at 40\\u00b0  ( seconds ) " TEXT, "Time to ft  ( m )  at 55\\u00b0  ( seconds ) " TEXT, "Max. height  ( ft ) " FLOAT)

If the gun used is the qf 12 pdr 12 cwt, what is the shell weight?
SELECT "Shell (lb)" FROM table_20821 WHERE "Gun" = 'QF 12 pdr 12 cwt'
SELECT "Shell (lb)" FROM "table_20821" WHERE "Gun" = 'QF 12 pdr 12 cwt'