sand blasting slow

Depending on the PSI you have available, you might also consider baking soda but it really has to be high PSI otherwise it only removes paint.

I'd say your sand isn't dry. How many moisture traps does the blaster have? I do a lot of glass etching and run a sandblaster often. Your issue sounds like poor media feed, usually do to moisture. While it's your buddies setup, 20 linear feet of steel pipe before the moisture traps will help get most of the air dry before it gets to your blaster. I run two traps, but plan on running a third but I live in Indiana and deal with a lot of humidity.