I haven't, but I like those pliars they use for gripping the ammo. Their video is the first I have seen with somthing like that. I noticed recently that Joerg uses something similar on his most powerful slingshots, but with a trigger mechanism.
slingshot rifles are not practical, all power bands lose energy if they remained stretched for any given amount of time. you can test it yourself shoot your slingshot without a pause to aim, then shoot a shot after holding your slingshot stretched for a minute or so. even without a chronograph you can tell the difference in lost energy. jeorg has tested, and will verify that.
Well, tell you what. It's proven bands lose only about 15% of their strength when stretched 20 seconds which is more than twice the time it takes me to load and shoot. My carbine is spot on accurate too. I would not hesitate to hunt with it at all if I hunted. I've only got a peep sight on it but a laser would work as well. I can band it up super strong and it makes no difference if I lose X percentage of elasticity, the thing is deadly. With arrows, sheesh...unbelievers are invited to stand in front of it at fifty yards if they feel safe...LOL... bent over preferably with their afterburners facing me. My underwater spear gun is also deadly in air or water and it makes no diff if the bands are cold, hot or been stretched a half hour either...it's powerful. If you want a carbine, make one. If you band it strongly it'll do you proud. Bill Hays and Jorg both inspired me to make one using both their design elements plus my peep sight idea...see pic or my gallery.