On high brass only suggests that something in the chamber that low brass isn't reaching. Looks like the mangled bit is pushed back to about where low brass would end!
You might want to yank the barrel, eyeball the chamber really well (magnifier if available). You might see an easily removed burr or such in the extraction groove.
(time passes slowly....)
Ok. Hadda get the skid plate and pan pulled on the Jeep tranny. Its drainin'. Back again!
I checked my own KSG. The extractor/extraction groove is at the bottom of the chamber where, incidentally, the shell will rub as it angles into the chamber. You got a sharp edge there, most likely on the outer two "corners" of the groove.
If so, pull that barrel and a few seconds with a Craytex (rubber) wheel on a Dremel will fix that. The "corners" are not critical, but don't hog things out either. Just a little breaking of the edges should do ok. IOW, it need not be "melted", just take the "sharp" off of things. I'd use a yellow wheel (very soft, not much cut) or if need be, the "Dremel" brand soft grey wheel, but lightly, as it will cut faster than a soft yellow one. You may want to reduce the diameter of the wheel a bit to better break the edges, and you can do that by holding the wheel against a brick, block, cement. Use a Qtip to get the dust and such out of the groove and a good clean with Hoppes/"your favorite" cleaner should get the remaining grit outta things. Reinstall barrel. Enjoy.
Thank you! I didn't take the barrel off but I did use a small piece of Emory cloth, cleaned it, put back together. I then cycled through the types of rounds I had, even some Estate 00buck, which I had problems with before. One of the Estate rounds caught, took it out and went through some other stuff. When I was done I went back to the Estate and it cycled through 25rds no problem! Thank you for the advice!