Silicon Carbide is the hardest sandblast media available. Aluminum oxide comes right after it. There are different grits of aluminum oxide and the number follows the same system as sandpaper. Most sandblast shops use 16 because it lasts longer. If I were do blast a frame or other substantive part I would use nothing courser than 80. I would never blast a whole car. Even sandblasting trouble spots like door bottoms will leave so much residual sand in the car, not to mention in the window mechanism, dash assembly etc.. that you will regret it for the life of the car.
If you really want to strip the car, use a chemical stripper on the large surfaces, but be careful not to get it into any seems. Near your panel edges and seems use a dual action sander to finish up the job. There are a lot of people that have used a DA to do the whole car. Use an open coat 80 grit paper and you won't do any damage.
I ran a body shop at one time so I speak with a little bit of experience on this.
