Colt Defense filed for Chapter 11 bankruptcy on Sunday, after a year of sharply falling sales and dwindling cash that made it hard for the company to meet demand for its sports rifles and handguns. A bondholder attorney told Judge Laurie Silverstein in Wilmington, Delaware, that Sciens was to blame for Colt’s inability to compete. Colt had planned to use the hearing to seek approval to borrow $20 million from its current lenders.