No, glass isn't out. It depends what it is though. Real glass bead can be safely used on a lot of plastics (at lower pressure of course), because it's a round(ish) bead that works by impingement (peening), there is no cutting action. The supposed "glass bead" that Harbor Freight and other chi-com sources sell though is not glass bead at all, it's ground glass, which cuts a lot like coarse aluminum oxide. Don't use that on plastic unless you're trying to change the surface finish, but if you're ok with that, it's not going to eat through the part or anything like that unless you really try hard. I'd set the pressure to no more than 40 psi for this.
You can feel the difference between real glass bead and ground glass just by rubbing some between your fingers. Glass bead rolls like little ball bearings (and the light reflection is pretty distinctive), while ground glass feels more like sand.
I agree though that soda blasting will take you a while. I'd be tempted to try laquer thinner, same as I use to strip krylon from aluminum AR parts, but try it on a small spot first. A lot of the plastics used for AR stocks are pretty resistant to solvents, but not all.
