I am pretty sure this has been used but I Just thought I would mention this. I know some people use a cookie cutter to make a trap bed. I tried an alternative method by using a 5.50in diameter hole saw with a piece of flat Bar welded across the top to pound it in the ground. It works well and pounds in hard ground pretty easy especially with the teeth on it. If you had the mandrel you could hook it up on a drill and make your bed. This setup works very well with 550s .

A wide chisel can make a quick bed especially in frozen ground