Circle Locating

A template is laid over the blank. The template’s center hole is used to mark the center hole on the back side of the blank. You can just use measurement or even eyeball the center, rather than a template.
The hole on the blank is drilled only very slightly into the back, just enough to accommodate the pins on the circle-cutting jig and the circle-sanding jig.

Circle Cutting

The blank is installed on the circle-cutting jig and the circle is cut on the band saw. I use a homemade jig with adjustable radius and adjustable depth stop.

Precision is less important on this step because the circle will be perfected in the next step, so you can use compass and bandsaw, or a compass and jigsaw. Your rough round will require more sanding to become smooth and round.

Circle Sanding

The round is installed on the circle-sanding jig. The "croze” (the edge of the barrel head which contacts the stainless steel can) is beveled to match the inclination of the can by adjusting the sander table angle. The croze is smoothed and its roundness is improved. I don’t know of a good way to do this other than by using a jig of this kind.