Am making sloppy joes for a party for 50 people how much hamburger would you recommend
You might get away with that, but unless your adding 10 pounds of Manwich - get 25 pounds of 80-20 ground beef and brown it evenly - pouring off as much fat as you can at the end. Re-season and serve on prison cafeteria trays.
About a 1/3 to1/4 lb per sandwich.
4 oz. per person should be plenty. If you were serving chicken or beef it would be 6 oz. per person.
For a party of 50, I would recommend 1/4 of hamburger for any sloppy Joes that you make. This is because the hamburger quantity will allow you to serve each person with a two-pound portion. For more details visit http://oldrecipebook.com/sloppyjoes.shtml and http://www.greatpartyrecipes.com/sloppy_joe_recipe.html.
I would have thought it would have been much easier to get a room full of Floyd's than 50 people wanting Sloppy Joes.