A: According to most distributors of sand filtration units, no. You can most definitely use this sand but you will be regretting it. The grains are too small and will end up causing more problems then the few dollars you might save buying the correct filtration sand from a pool supply store or online. Hope this helps.
A: You never want to fill a punching bag with sand, it will settle and get as hard as concrete. When you hit it, there's a good chance of you shattering your fist. Instead you should use, old clothes or waste paper to fill up a punching bag.