Ooo I have a significant update! Story time.
I was disappointed that my new hiking sling wasn't cracking when I threw rocks. It worked ok for tennis balls(not great, but it would give a little crack), but as soon as I switched to rocks, nothing. I threw hundreds of rocks trying different throwing techniques(balearic, byzantine, greek), different wrist angles, different strengths and couldn't get it to crack a single time.
So after an insane amount of testing different factors, I ended up isolating it down to the pouch design preventing the crack. It's due to the same effect Acroballistics describes here in his LP-4 video about the smooth unrolling of the pouch and pouch/cord connection(also see attached gif of his demonstration):
https://youtu.be/rKbaOivX85w?t=78Acro covers it in his video due to accuracy and release feel, but when combined with my original info in this thread about what actually causes a whipcrack, it becomes fairly obvious what the problem is. If the pouch and pouch/cord connection can't smoothly unroll, it won't create a traveling loop on the release cord, and thus there will be no loop at the cracker to crack. To reiterate from above, no matter how fast you swing it, it cannot crack unless there is a traveling loop.
Back to my story: the reason my hiking sling won't crack at all with rocks(and only barely does with tennis balls) is because it is a standard seatbelt sling design with a big honkin' stiff nail knot(highlighted in my photo below) that holds the pouch to the release cord. This creates a long(nearly two inches), incredibly stiff point in the release cord which interrupts the smooth unrolling of the cord and thus creates no loop to crack further down. The only reason tennis balls would crack slightly is because their diameter is so large that the knot was touching the side of the tennis ball and thus the tennis ball would impart some energy to the knot and some to the release cord directly, enough to get a weak crack.
Aaaanyways, I confirmed this by testing the exact same cracker on a couple of different slings(literally, the same piece of cord untied and retied to a new sling, pictured below). These slings are all exactly the same length(28"), same weight (14-16g) and all use the exact same brand paracord(with the exception of the dyneema sling of course). The only difference is in the various pouch designs, and they each behaved predictably given this new information.
- The seatbelt sling we've covered.
- The sheet bend sling ("good" in the photo) has a bit of a stiff spot because of the sheet bend, but cracks much better than the seatbelt sling since that knot is much smaller than the nail knot.
- The pouch with grommets was next, and I think is better than the sheet bend because the loose bowline around the grommet allows the release cord to actually rotate freely inside the grommet. I believe this negates the small stiffness from the grommet and allows the motion to transfer more freely to the release cord and make a better traveling loop for the crack.
- And best is the nearly-knotless which of course has no stiffness at all because there are no knots and creates the smoothest traveling loop.
I'll add this property to my list above, but this is definitely something to consider if you're looking to get a good crack!