If that's what you can get, it'll be just fine. You may want to upgrade pretty quickly though so think about that.
Be very careful of anyone that says you NEED a certain type of gun. A fella named Eric Miller has won dozens of matches overall with an old Remington Sportsman 48 shotgun. Jerry M does pretty good with a Mossberg shotgun named after him too. If cost isn't a concern, a Benelli shotgun worked over by Mike at Accurate Arms, a JP CTR-02 Rifle and a tricked out 2011 by a custom gunsmith is your best bet. For us common folk, your current pistol and about 5 magazines, the aforementioned 870 and any ol' AR will get you into it. If you like it, you are a .308 rifle away from having a real heavy metal setup. You can always trade up later.