That is fine. And in that case, the gun has no real bearing on the issue since the crime itself (the taking of a life or property) is what is at issue.
The notion that there can be any crime which strictly revolves around the posession of a gun or failure to register or pay a tax for the "privilege" of carrying or owning a firearm is in error since the 2nd amendment is quite clear about the federal government's role.
Furthermore, the federal government is not authorized anywhere in the constitution to prosecute crimes other than the three listed as falling under federal justisdiction: Treason, Piracy and Counterfeitting.
In this case, we have the federal government filing a CIVIL suit. Something they should be barred from doing.
Regarding federal crimes, the founding fathers supported federal crime laws. How does this fit with your contention that the founders disapproved of designating offenses as federal crimes?