user: Question: What is the rear sight type on the model with the ACR muzzle brake device? 
Columns: ['Colt model no.', 'Military designation', 'Barrel Length', 'Barrel', 'Handguard type', 'Buttstock type', 'Pistol grip type', 'Lower receiver type', 'Upper receiver type', 'Rear sight type', 'Front sight type', 'Muzzle device', 'Forward assist?', 'Case deflector?', 'Bayonet lug?', 'Trigger pack']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['601', 'AR-15', '20 in (508mm)', 'A1 profile (1:14 twist)', 'Green or brown full-length triangular', 'Green or brown fixed A1', 'A1', 'A1', 'A1', 'A1', 'A1', 'Duckbill flash suppressor', 'No', 'No', 'Yes', 'Safe-Semi-Auto']
SQL:

assistant: SELECT "Rear sight type" FROM "Table" WHERE "Muzzle device" = 'ACR muzzle brake';