A few more:
We used less colouring in each cup. We also put a few drops in the cup immediately prior to the photo for added effect. There are some interesting effects happening... The Ikea cup glass is different (probably very poor quality). There appears to be cavitation or some other effect happening on the left side of the cups.
Unfortunately the Ikea glass behaved differently. We couldn't get a good shot of the pellet travelling through the cup, as the cup would instantly explode.
https://flic.kr/p/GEkVRMIMG_0056 by Tyler Gerritsen, on Flickr
Thanks for looking!
Out of interest is the glass you used in the first shot of this series from a different batch that the others? It seems as if the crack propagation speed is a lot faster for that one than the others in the series. I would expect that better quality glass would be harder than cheap, and so the cracks would propagate faster, in just the same way that the speed of sound would be quicker. Out od interest how are you triggering the flash? Acoustic off of the muzzle crack? I think that I might have a go at getting some shots of clays being hit by a shotgun, that should be pretty spectacular. I have some studio strobes, so all I really need is an easy way to trigger them, which as I have a degree in electronic engineering really shouldn't be too difficult.