I tried the dry ice method. all I have to say is holy shit.

I ran with crushed dry ice and 45 micron first, shook for about 2-3 minutes. Then, switch to 220 micron and shake until it starts to get a little darker. Then, I start a new pile, and shake for the last pile which I'll cook with.

shake ~gently~ for best results. no rushing, it goes very fast anyway!

it's the quality of bubble without the water, and the highest yields of any method I've seen.

I also tried adding some crushed dry ice to the tumbler, which produced a fine product as well.

thanks for the tip!