Thanks for the info. I haven't done any research on small arms which is probably what you are looking for. The holdings of the National Archives within Record Group 156 are huge, with some thousands of different entries listed in the "finding aids" book. That book for RG156 is about an inch thick, has standard 8.5x11 sheets, double-sided, an average of maybe 15 entries per page, so there is a LOT of stuff. Some weapons are covered from many different angles, beginning with the contract records, then there may be inspection records, issues, inventories at various locations, etc. etc. One type of record which is faster to use is the ledgers. The kind that takes a lot more time are the correspondence files, which are often multi-page letters folded in thirds, filed end-up in special "shoe-boxes."
Then there are the various archive locations. The main building with text material is in Washington DC. The "Archives II" with graphic materials and a lot of other things is in nearby College Park MD. Then there are many regional archives which will often also hold ordnance records peculiar to their area, such are records from an arsenal.
I've used the extensive records of Allegheny Arsenal which are in the Philadelphia branch of the N.A. I actally found some of my cannons listed specifically by type, date, and registry number, which had passed through Allegheny Arsenal.
If you list more specifically what you are looking for, some of the CMH small arms experts will probably be able to tell you where to look in the Archives collections.
To Join the Company of Military Historians click here