fedex has a triangle shipping tube but you have to use it on express mail. OK SO take the tube --it's free. Take some black paint and spray over the fed ex label and writing all over the outside and then ship it fed ex ground. Works great and they never said a word about it. motordoc
I use 4" ABS drain pipe with glued and screwed rubber cap on one end and hose clamped rubber cap at the other end. I wrap the barrels in bubble warp. I have ten round trips all around the country with same pipe with no problems. I've shipped receiver and barrel together a couple of times. I like this reusable set up better than all the other methods.