Not being a lawyer if it matter hire one.
A) Well the fact of civil law is party A can sue party B for any reason and in the US only needs to file a claim that from my understanding only costs a $350 dollar filing fee so a lot of times it does not come down to what is right or wrong as to fair use but who has the better story as to their claim of infringement. Typical for example Disney does not care if they will win or loss under the scope of fair use but rather using the process to protect what they “feel” is their IP property by default even if it falls under fair use doctrine so if you made and make use of an asset that looks close to Mickey Mouse except at the very least a cease and desist notice.
B) If an asset element is based on an asset paid by taxes then it’s fair use under public domain. For example the White House is built using taxes. NASA is a civilian based organization once again paid using taxes so assets like the shuttle are pair use.
C) Weapons in most cases is fair use as to letters and numbers can not be copyrighted (even though Apple will have you believe other wise). The 1911 for example is out of patent and there are hundreds of manufactures so who would sue you?
D) Avoided the use of branding. Calling the 1911 the Super Gun 1911 = OK but calling it the Colt 1911 is a different animal and a case you would probably loss.
E) In all cases refer to A.
That out of the way in most cases you don’t need a lawyer but rather have an understanding of copyright and the issues in the same way one understands the finer details of baseball that goes beyond the average fan and once you get into it you will have a better idea what to do the day the paper work starts arriving in your mail box 
Check out Leonard French’s channel
P.S. Be aware there are more people out there who have no idea as to fair use and are usually the ones causing the most problems so always question what seems legit.