No, CCI will not cycle a sigma. Empty case will get stuck in ejection port. The rifleling in the barrel will produce a doenut pattern out to about eight feet. A smooth bore is best for a tight pattern with shot. If you were dealing with a snake, think you would have better luck with a shovel.
I've had it cycle. But the 8 feet is about right. But after 4 shots in about 2 seconds it did what it was supposed to. Haven't had to use it any more but I still carry it with me when I'm out on the trails in my Rhino.
If I had to depend on a handgun to deal with snakes, I'd not even consider a .40 or 9mm auto-- I'd get a Taurus Judge or use my old Koon Snake Charmer.