Don't plan on the same wall thickness. Things don't work that way. Plastic piping is always thicker walled than metal for a given ID, at least for common materials and usage. But I'm pretty certain your assumption on the ID is correct.
Bill's thoughts on Static Guard are worth looking at. I don't know if the coating wears off or loses potency. Time will tell.
I'm thinking a homemade metal auger may be better than a plastic one, simply for wear and tear. I suspect the sand is going to be abrasive as heck, especially to plastic. Not exactly certain how to construct one. That's a bit above my pay grade! But you may get some ideas from pictures of stokers or farm equipment. I think augers are used in grain harvesters.