As with all investments, you have to be careful in the world of firearms and militaria. A pair of 20-century infantry books from the Argentine army isn't worth much, but a full set of medieval body armor can net tens of thousands of dollars. One of the most lucrative investments a person can make is in U.S. Civil War artifacts. Flags are especially valuable. A Confederate battle flag can be worth as much as $100,000. Civil War dealers are always on the lookout for artifacts with good provenance. Groupings of such items -- uniforms, letters and medals -- from the same soldier are expensive but hold their value well.
When it comes to antique firearms, the buyer has to beware. One of the main concerns collectors have about buying rifles, muskets and other weapons, is how much repair and restoration work the piece has had. Some repair work won't impact the value of a firearm, while too much work could greatly influence the price. The key is to know the difference, and that mostly comes from experience.