Wheel refers to a poker table. Beans refers to the number of players. There are certain poker games which require ten cards per person, and there wouldn't be enough card for six people to play in a 52 card deck....
"Five Beans In The Wheel"
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
As a safety practice, many Old West gunmen loaded five cartridges "beans" in their six-shot revolvers so they could leave the pistol hammer resting on an empty cylinder chamber, a precaution designed to prevent the gun from discharging accidentally.