JACKSON, Wyo. (AP)  An unknown number of dud artillery rounds litter the slopes above a remote pass inside Yellowstone National Park. But there are no plans to find and safely detonate them or stop the avalanche control program that uses artillery shells to keep the pass open during the winter. One National Park Service study estimates around 300 unexploded shells above Sylvan Pass on the east side of the park, but Yellowstone officials say no one knows the real number.The Associated Press reports at least one artillery shell was found on the highway that goes through the pass.Despite the danger, Yellowstone's proposed winter use plan would continue the practice of using artillery to keep the pass open over the winter. Public comment on the plan ends Monday.