Old shotguns using new shells

[Fishwhere]

Hey there,

First off I am an absolute noob to this stuff so be gentle haha. But I had plans to shoot an old shotgun my grandpa has but I thought I heard you have to shoot steel shot now instead of lead. And the issue being that older shotguns cannot shoot the steel shot supposedly.

Can guns shoot both steel and lead?

Another side bar of this could also be that the skeet range we went to once may have stipulated the steel shot - so I could be messing up my facts as well on what can be shot where/when.

And another thing is where is the best deal and place to get cheap shotgun ammo for skeet shooting. What is a good price?

Any clarity would be appreciated.

Thank you!