I obtained this from the Gift Shop, an underground storage area you gain access to after completing the main story missions in Claptrap's New Robot Revolution DLC (DLC 4)
The 101101 Cannon is a very powerful Rocket Launcher, has a very good push back ability as well. As with all Eridian Weaponry, it has infinite ammo!!
Essentially it's a recharging clip, after depleting the mag you have to wait around a minute for it to fully recharge. You can, however, fire off rounds before it's fully charged.
Always prevelant to keep one of these in your inventory in case you manage to run out of ammo with everything else.
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