Denis,
Nice. I have a cheap Mossburg similar to the 1300.
The first round is regular bird shot, the rest are #2 buckshot. Mine is a 20 gauge so your options are different. Some good links:
http://www.gunsandammomag.com/cs/Satellite/IMO_GA/Story_C/The+Home+Defense+Shotgun
http://www.internetarmory.com/shotgun_ammo.htm
I really recommend some time in the desert...these type of shotguns do require some acclimation.
