.AVI is uncompressed video and will generate large file sizes. You might want to look here ( http/www.bandicam.com/support/settings/video/ ) for an explanation of the video settings and see if that helps.
Just as a tip as well incase you get serious with Bandicam... If it's the same as fraps (I presume its very similar!), the faster your hard drive, the higher your fps in game, again presuming it you are using it for capturing game footage. a normal 7200 rpm drive will drop your fps from 60 to roughly 30, an sdd will give more and 2 ssd in raid 0 will drop very little fps. Also bare in mind the higher fps you are recording in game, the more space the file will require!
Probably useless info, but it may help someone at some point