Drawback delegation: Commissioners may determine and provisionally grant duty drawback subject to bonds and government review. Amendments delegate determination and provisional grant of drawback to the Commissioner of Central Excise or the Commissioner of Customs and Central Excise, subject to applicants filing within sixty days (with a possible thirty day extension for sufficient cause), stating materials, proportions and duties paid; provisional payments may be allowed against bonds and are adjustable against final drawback, while the Central Government retains power to revoke or direct withdrawal of rates or amounts determined.