CREATE TABLE table_204_343 (id DECIMAL, "nation" TEXT, "model" TEXT, "length" TEXT, "barrel length" TEXT, "weight" TEXT)

which rifle has the longest barrel ?
SELECT "model" FROM table_204_343 ORDER BY "barrel length" DESC LIMIT 1
SELECT "model" FROM "table_204_343" ORDER BY "barrel length" DESC NULLS LAST LIMIT 1