You'll probably find that the papers etc. were split up among his children and have spread out from there. You'll need to track all those descendants down to be sure you have found it all.

Are you planning on writing a biography of him? He certainly deserves one.

If guns are not your thing, that would be a steep learning curve to cover that aspect of his life. Of course that is the aspect that most people would want to read about.

If a biography is your intention, perhaps you can find a collaborator who is already a student of A.H.'s guns who could work with you on that aspect of it.