00, think nine .357 magnum rounds all at the same time . The first two rounds are 00, then slugs if I need to dig deeper into the tube. I added a night light to mine which I really like since I live out in the weeds and it better than fumbling with a flashlight if I have to go outside when things go bump in the night.
I would never trust my life to birdshot, just not enough energy.
"Life is tough, even tougher if your stupid" John Wayne
. The first two rounds are 00, then slugs if I need to dig deeper into the tube. I added a night light to mine which I really like since I live out in the weeds and it better than fumbling with a flashlight if I have to go outside when things go bump in the night. 
