I have heard from friends in local law enforcement that the feds are suddenly taking violent gun crime very seriously. Apparently, for the past several years, it was nearly impossible to get the feds to prosecute a gun case involving repeat violent felons, but in the last few months they have been taking taking bunches of local cases for federal prosecution. The general consensus seems to be that they have received very different marching orders under the new administration.
As far as prosecuting stolen guns, those are almost always done locally and King County prosecutors generally interpret the law to mean that cops have to prove the person holding the stolen gun knew for sure that it was stolen (not just "reasonably should have known..."). Basically, the cops have to catch them in the act of stealing it, or get a statement from the suspect that they knew it was stolen. Hence, stolen gun prosecutions are very rare in King County. Oddly, they don't always apply the same rigid standard to other types of stolen property (cars for example).