Most people recommend BB's or #2 if you are shooting steel. But you can even go to #3 or #4 depending on how close you can get them. With crane you can also shoot lead if you want. I went last year and killed them stone dead with 3 inch #2 steel.
You can use lead for crane only. But you better not shoot a goose and have a lead round on you. I shoot steel in case the chance of a goose or duck presents a shot, you can take them too.
What is the typical ammo size for Sandhill crane? I may be going hunting this season and wanted to start looking now.
Always used BB's and #2's.
And a little advice. Don't shoot for the body, they can take allot of lead, shoot for the wing. You can put a lot of pellets in the breast and they'll keep going but you bust that wing and they're coming down.