If you are shipping a 1.2 – 1.5″ diameter barrel you can use either 1 1/4″ or 1 1/2″ Schedule 40 tube. You could even use 1″ tube for a Savage barrel-nut type barrel. See ID dims here – https://formufit.com/pages/pvc-pipe-size-dimensions-chart.

Wrap each end of the barrel 1-2″ from each end using 1/16″ thick, adhesive-backed rubber (see https://www.zoro.com/search?categoryl1=Raw+Materials&variants.attributes.4114=1%2F16%22&categoryl2=Neoprene+Rubber&q=&variants.attributes.7712=Adhesive). [You’ll find this stuff has a ton of uses, e.g. strips along the bottom of a piece of lumber for use with various reloading tools.] Cut 1-2″ wide strips and keep wrapping around the barrel until you have a fairly close fit inside the tube at both ends.

Next, cut a couple of strips of the rubber wide enough to fit inside the PVC caps and tube. Role them into little balls. One ball goes at each end of the barrel tube.

Make absolutely sure that the second cap goes on such that the barrel is under pressure from the rubber balls and caps and CANNOT move back and forth.

PVC tube can be easily and quickly cut with a normal wood saw with fine teeth – no need for a tube cutter.

For threaded barrel sections, and end faces, just use duct tape.

I secure the caps with 8 long pieces of duct tape – a cross shape at 45 degrees to a cross shape – and then wrap duct tape around those pieces 3-4 ” down from the cap to reinforce the end tapes.

As with all labels, tape over the entire label with clear packing tape.

The above process has worked excellent for me shipping barrels up to 65# and 45″ long. And, when done, you can store the barrel in the tube you shipped it in.