To get a square cut, clamp a quality stainless steel hose clamp around the barrel as a guide for your saw blade. Use the finest steel saw blade you can find, with no offset to the teeth and no waves. Most hacksaw blades have every other tooth offset to opposite sides, and have a wavy blade, but there are fine ones that have just straight teeth. After you get done, use the hose clamp as a guide for your file, then for a whetstone.
