Complex sentence: While the military use of the flintlock declined after the adoption of the percussion cap from the 1840s onward, flintlock rifles and shotguns remain in use among hobbyists used in the United States.
Split into simpler sentences: While the military use of the flintlock declined after the adoption of the percussion cap from the 1840s onward. Flintlock rifles and shotguns remain in use among hobbyists used in the United States.