CREATE TABLE table_23430 ("Colt model no." CLOB, "Military designation" CLOB, "Barrel Length" CLOB, "Barrel" CLOB, "Handguard type" CLOB, "Buttstock type" CLOB, "Pistol grip type" CLOB, "Lower receiver type" CLOB, "Upper receiver type" CLOB, "Rear sight type" CLOB, "Front sight type" CLOB, "Muzzle device" CLOB, "Forward assist?" CLOB, "Case deflector?" CLOB, "Bayonet lug?" CLOB, "Trigger pack" CLOB)

What is the rear sight type on the model with the acr muzzle brake device?
SELECT "Rear sight type" FROM table_23430 WHERE "Muzzle device" = 'ACR muzzle brake'
SELECT "Rear sight type" FROM "table_23430" WHERE "Muzzle device" = 'ACR muzzle brake'