Place the combination damper/collar on the top of the barrel stove near the back. Use a scribing tool to trace the collar opening onto the barrel.
Drill two or three 3/4-inch holes through the barrel along the inside of the collar tracing using a cordless power drill and a 3/4-inch all-purpose drill bit. Space the holes evenly around the traced circle. Make sure to position the holes close to the traced line. The holes will help you maneuver around the traced circle with a saw.
Attach a metal-cutting reciprocating saw blade to a reciprocating saw. Insert the blade into one of holes you drilled along the traced line. Saw along the traced line to create an opening for the stovepipe in the barrel. Use a metal file to smooth the edge of the opening.
Place the combination damper/collar back on the top of the barrel stove. Line up the inside of the collar with the hole you cut in the barrel. Mark the mounting holes on the damper/collar onto the barrel with the scribing tool.
Remove the damper/collar. Use a 1/4-inch all-purpose drill bit to create mounting holes in the barrel.
Reposition the damper/collar on top of the barrel stove. Mount the damper/collar onto the barrel with the bolts provided with your barrel stove kit.
Slide a length of 6-inch round stovepipe into the barrel’s damper/collar. Attach the stovepipe to the damper/collar with 1/2-inch sheet metal screws driven through the screw hole opening around the top of the damper/collar.