With the new ammo laws, do I still need to have a back ground check to buy ammo that I use that day?

Yes

If you bought your weapon after 1990 you should have already been checked and on file. You will need the number of the Bacground search form from FFL/DEALER. If not then you will have to pay $19.00 and wait about 30 minutes according to NRA. Hope you saved your paperwork.

As long as you dont take any ammo home and use it all there you dont have to do a background check. I would still call them to verify