One of the United States' most venerable firearms manufacturers has filed for bankruptcy protection.The 179-year-old gunmaker Colt Defense, maker of M4 carbines and M16 rifles used by the US military and other armed forces, filed for bankruptcy amid delayed government sales and declining demand.Colt's business was hurt when it lost a 2013 contract to supply M4 carbines to the US military, said Pimm Fox, an analyst speaking on Bloomberg television. Colt had held the contract for more than 80 years.About 7 per cent of the Hartford, Connecticut-based company's business is tied to the US military, Fox said.The company's financial problems reached a head in May when it missed an interest payment. A 30-day grace period expired Sunday, forcing the bankruptcy filing.Fox said the company's business had been affected by "a lot of discounted weapons that have come onto the market, which has displaced the weapons that are made by Colt."While firearm sales in the US are up, most of the buyers are people who already own a gun, making the cheaper weapons a more likely choice.Colt Defense said it expected the bankruptcy process would speed up the sale of Colt's business operations in the US and Canada."Colt intends for the sale to ensure a smooth and swift transition of the business with all of its iconic brands, products, and operations supported by a stronger balance sheet due to a significantly lower debt burden," Colt said.The company intends to continue normal business operations. It plans no layoffs, and the current management will be maintained throughout the restructuring process, it said.In its long history Colt has had frequent financial problems, including a bankruptcy filing in the 1990s.The company was founded in 1836 by Samuel Colt, who obtained a patent for a revolver with a cylinder holding six bullets. This technical development meant the gun could be fired six times without reloading.Colt initially had difficulty selling the new firearm and had to close its first factory in New Jersey. In 1855 the Colt Manufacturing Company was founded, and when the US Civil War broke out a few years later its revenue boomed.