Gary
SE Kansas
turn the snail trap 90*
then you make the back/top panel the striking panel and you run it all the way into the drum.
after that regular steel can be used and shaped to form the drum.
a flat bottom and a 45* top would work well enough.
Here's how I did mine; back or strike plate 1/2" plate; sides and bottom 1/4" plate; bottom or collecting vessel is 6" thick wall pipe that has a small section removed. The side has a small door that allows for collection of lead.