Complex sentence: After Colt's patent expired in 1857, other manufacturers began producing double action revolvers, but Colt's Manufacturing did not manufacture its own double action revolver until 1877, twenty years after the patent had expired.
Split into simpler sentences: After Colt's patent expired in 1857, other manufacturers began producing double action revolvers. Colt did not manufacture its own double action revolver until 1877, twenty years after the patent had expired.