Kevin, not trying to say I know everything about blasting.I did a lot of sample blasting in previous occupation for customers.Everything from steel shot to 400 grit oxide.The biggest 2 issues were how much pressure you use and what surface finish was desired and that was the deciding factors in grit size. There are some heavy primers today that fill some of the surface roughness.The issue of life was rather parts were reasonable clean so grease /oil didn't contaminate the media.The majority of our customers were mfg new parts so normally wasn't a problem.A lot of new castings are blasted.....The guy with the gunstock caused a lot of laughs at his expense....Al. Oxide lasts much longer so if you compare cost it is competitive with the price of sand without all the dust... As for the guy with the gunstock if he never used it he should have tried it on an old piece of wood first.. Harbor Freight stocks it in 70 grit and it leaves a nice finish on metal..
Martin, what you're saying is the application drives the choice of media for a variety of reasons. Well said and I totally agree..I did my 30 years of self employment so I am semi retired but as a general rule aluminum with glass bead and steel and iron in aluminum oxide. I don’t like to blast blocks because their are to many areas to trap the media and is very damaging to the internals if you can’t get it clean after blasting. If you only want to have one type of media I would choose glass bead.