First you go on forge, then once you have done that go to the beach on Last Resort.

But before you start you should make sure that unlimited ammo is on.

Then once you're at the beach press the up button and select a countainer, open, flip it up side down.

Then select a barrier and place two of them in the countainer. g

Get a gravity lift and place it in the countainer and get in, use the grav lift and it should send you really high!