Adams Arms, Inc. sued Sig Sauer Inc. for infringement of U.S. Patent No. 7,971,518 (the 518 patent) in the U.S. District Court for the Middle District of Florida. The patent covers a retrofit system to convert AR-15 and M-16 rifles from a direct gas impingement system to a direct drive system. This lawsuit appears to continue a feud between the companies involving U.S. Patent No. 7,469,624, the parent to the 518 patent. The present case no. is 8:11-cv-01473-EAK-TBM, filed on July 5, 2011.