There's lots of choices, research the archives here and on TFL to see beaucoup input.
Short answer, there is NO easy and quick answer that's the best choice for all situations.
Right now, buy ammo(The cheapest field loads you can find), use up,repeat. That's usually shown here as BA/UU/R. You have a ways to go before that 500 can be safely and effrectively used.
Good move,trashing that PG. Kudos!.
And, some basic lessons from a QUALIFIED instructor can save you cash and time. Second choice, read these archives over and over.
Last Choice, a split between Action Movies and gun shop commandoes..
HTH....