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

how many other models are the same length as the m1898 carbine ?
SELECT COUNT("model") FROM table_204_343 WHERE "model" <> 'm1898 carbine' AND "length" = (SELECT "length" FROM table_204_343 WHERE "model" = 'm1898 carbine')
SELECT COUNT("model") FROM "table_204_343" WHERE "length" = (SELECT "length" FROM "table_204_343" WHERE "model" = 'm1898 carbine') AND "model" <> 'm1898 carbine'