A 24-year-old Lowell man is facing armed assault charges and several firearms violations following a Sept. 26 altercation on Gold Street that left one man bleeding from a gunshot wound to the back. That man was transported to a Boston hospital for treatment. His alleged assailant, 24-year-old Ricky Sin, was arrested several blocks away a few hours after the shooting. Sin is well known to Lowell police. Police officials said the violence may have stemmed from a dispute between the two men over an unidentified woman.