FYI: Almost all cannons/tubes that you see on GAR monuments or in cemeteries are still the property of the United States. At the end of the last century, the military "loaned" (a term used on most archived documents) the guns to a specific GAR post. THis has allowed the Sons of Union Veterans of the Civil War (SUVCW, the heirs to the GAR and chartered as such by Congress) to block the sale of these historic items and, in some instances, to succesfully sue for their return.
A 32 pounder Bureau Ordnance rifle was "given away" and hauled off from a cemetery in San Luis Obispo, California, as a committee thought it was an eyesore. By obtaining documents from the National Archive that showed that the gun was on loan and still belonged to the military, we were able to get it returned, and after being restored, is the centerpiece of the GAR plot.