Question: Name the barrel length for rear sight A2 for Factory compensator
SQL: SELECT "Barrel length" FROM "1-12834315-4" WHERE "Rear sight" = 'A2' AND "Muzzle device" = 'Factory compensator';

Question: Name the barrel twist for colt model MT6400
SQL: SELECT "Barrel twist" FROM "1-12834315-4" WHERE "Colt model no." = 'MT6400';

Question: Name the forward assist for A2 barrel profile
SQL: SELECT "Forward assist" FROM "1-12834315-4" WHERE "Barrel profile" = 'A2';

Question: Name the stock for colt model MT6601
SQL: SELECT "Stock" FROM "1-12834315-4" WHERE "Colt model no." = 'MT6601';