user: Question: What's the type of muzzle devices on the models with Round hand guards?
Columns: ['Colt model no.', 'Name', 'Stock', 'Fire control', 'Rear sight', 'Forward assist', 'Case deflector', 'Barrel length', 'Barrel profile', 'Barrel twist', 'Hand guards', 'Bayonet Lug', 'Muzzle device']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['601', 'AR-15', 'A1', 'S-1-F', 'A1', 'No', 'No', '20 in.', 'A1', '1:14 (early) or 1:12 (late)', 'Triangular', 'Yes', 'Type 1 Duckbill/Type 2 Duckbill']
SQL:

assistant: SELECT "Muzzle device" FROM "Table" WHERE "Hand guards" = 'Round';