As RHD45 pointed out, the biggest reason for Roosevelt to have given Mr. Harwick a shotgun is if Mr. Harwick was an avid shotgunner. If you cannot see this then you are being shortsighted. It is the height of generosity to bestow a gift, on a friend, of an item that you yourself have little interest in. It shows admiration and unselfishness to go to the effort to acquire a gift that the recipient will be sure to appreciate and enjoy. It is easy to believe that Harwick and FDR could have had some interesting talks about the personal interests of each during FDR's stays at the Mayo Clinic.
I agree it would be far-fetched for Obama to give the administrator at WR a Colt SAA, but certainly not for GW Bush to do so, if he knew the man had an interest in them.