CREATE TABLE table_203_253 (id DECIMAL, "model" TEXT, "frame" TEXT, "years mfg'd" TEXT, "caliber ( s ) " TEXT, "production" TEXT, "barrel" TEXT, "notes" TEXT)

what model revolver had the least number of revolvers produced ?
SELECT "model" FROM table_203_253 ORDER BY "production" LIMIT 1
SELECT "model" FROM "table_203_253" ORDER BY "production" NULLS FIRST LIMIT 1