You don't need rolls. I simply make a former and bend the sheet around it. You will need to keep annealing the sheet between bends as it will work harden. Fully annealed copper is surprisingly soft and bendable.

Andrew.

Has your local ME society got some larger bending rolls? – mine has. Where are you approximately in the country?

LBSC recommended bending boiler shell round a downspout. I don't! I'd take up Noel's suggestion, one anneal will get you from flat to round at 5" diameter. However, if you're aiming for the usual 80-100 psi working, you can get away with 13g for a round shell, more difficult if the back end is opened out for the firebox outer wrapper. If you go down this route take your boiler inspector along with you

Copper sheet is expensive, especially if you stuff it up and have to buy a second sheet. A set of slip rolls is also expensive and a costly ornament if you do not have another use for them.

For a one-off project, best to take the plate to a local engineering business.

I am surprised that (Unless Peter has has a personal message) nobody here has offered to roll Peter's barrel.

Bob

I’ve rolled 3 mm copper using large rolls donated to the club. I had to keep annealing it with my 2944 burner. Rolled to 6-1/4” with slight taper. The member who donated them moved away and some time later they vanished. He undonated them! Hardly anyone is going to have rolls big enough. I suggest making a former from stacked plywood disks. With multiple annealings and using hands, hammers and band clamps, it can be done. Buying 5” tube would be so much easier.