Besides books and articles, historical government and archival data can be useful for Second Amendment research. The links below will provide access to congressional proceedings, historical U.S. law, and more:
This library unit, located on the 4th floor, contains a wealth of primary sources, especially on topics that would have been studied, reported, or debated by the federal or state government.
Use this database for primary source material, such as congressional documents and reports, 1817-1980.
Like the Congressional Serial Set, but covering the years 1789-1838.
Historical Statistics contains quantitative data on demographics, work and welfare, governance, and economics.
Below is a list of some broad-coverage digital archives and government search portals that can be found online. You will most likely need to seek out specialized digital collections in addition to these more general sources.
This easy-to-use congressional website provides access to current and historical legislation, as well as congressional records and committee reports.
The Internet Archive is an immense collection of original documents, photos, open source books, and other odds and ends. With over 7 million books included, you are bound to find something on your topic.
This ongoing digitization project features collections of books and articles from universities around the world.
The Library of Congress is in the process of digitizing historical American newspapers. Currently, high-quality, searchable scans are available from 1836-1922.
This Wikipedia list includes links to various newspaper archives.