I use 6" x 6" or 8" x 8" x however long I need for the outer layer. I use cheap, less than $5 locally, U-Haul moving blankets to wrap the rifle or action up. I unfold the blanket and place the rifle or barrelled action on the closest edge centered from side to side and roll up 3 to 4 times and then fold the the ends in like a burrito, finish rolling it up. Seal one end of the box, place the action or rifle in the box to figure out the length needed. Cut the corners to allow the box to fold closed as normal, trim off the excess, remove the burrito, cut the excess pieces to fit inside each end to reinforce the package, throw a few in the bottom, put the burrito in the box, throw a few excess pieces on top and seal it up. Use good heavy duty packing tape and seal it up tight, it's almost idiot proof at this point.
View attachment 214359