Hey, thanks a lot for all the questions. I really enjoy thinking about and discussing this stuff. I'm not an expert by any means. I'm just interested in the subject and I've done a little reading.
It's hard to say what the variation is. On one hand, it's the same substance, it's all gelatin. On the other hand, the theoretically less consistent food grade stuff could yield inaccurate results. On a hypothetical third hand, my results with Speer Gold Dot .40 S&W and Prvi Partisan .223 were consistent with professional results.
I just use cheap Sterlite plastic bins bought from Walmart. I originally wiped them with a light coat of vegetable oil but that's not really necessary. You just pull out on the wall of the tub while holding the surface of the gelatin and that pops it off each side, then you turn it over and gently shake it. Not very hard, really. It's pretty solid when it's properly mixed.
I have not tried higher concentrations. The older standard of 20% is more expensive, is not the current industry standard, and there is less documentation available for what to expect.
I don't have any experience with the real stuff.
I wouldn't attach any exact time to how long the block can sit out but if it warms up too much, the results will probably be effected. What's most important, in my opinion, is to calibrate with the BB immediately before conducting the test shots. If you don't just leave the block sitting out it the sun for half an hour while you screw off and if the BB calibration is withing tolerance, the results ought to be reasonably accurate, I think.
I don't have a high speed camera. Without that, you're not going to be able to clearly see the bullet passing through the medium.
I shoot by hand. I don't expect that changes in angle will make substantial differences in test results so long as the bullet stays in the block.
I post this stuff to several different forums and I don't always remember to update but I always post to my YouTube channel so you can always check up there. Here are a couple of the latest ones:
.223 69 gr Prvi Partisan BTHP:
10mm 200 gr Black Talon: