I have shipped several guns in old leg of mutton cases. Acid free paper wrap over the entire gun, bubble wrapping, small bubble size, the stock, barrel and for-end makes a real tight fit in the case. Then I wrap the case in foam wrap, put in a double thickness cardboard box and fill any areas of space with either foam peanuts or the air filled packing bags which are getting very popular. This makes a snug, well protected package which has traveled well.
Long guns, rifles, are shipped in a plastic case with four or five layers of protection. Never a claim and hope to never have one. Have had several receivers make remarks about over kill but I ask each of them to return it just like I shipped it. Easy for them to do as all the material is right there and they just have to reassemble when done to ship. A few have made positive remarks about the level of packing and have told me stories about what junk packing others use with very bad results. I would rather pay five dollars more in postage than have to file a claim.
