I have a 55 gallon drum offset with an expanded metal grate and this is what it can cook at the same time:
6 pork butts
3 turkeys in half pans
3 briskets, packers
4 untrimmed racks of spare ribs
To add a bit more capacity, I made a second self using carriage bolts for legs and a replacement grill from the big box hardware store. It can hold:
3 pork butts
2 untrimmed racks of spares
1 huge brisket, packer
I hope this helps giving you some idea what a horizontal 55 gallon drum can hold.
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