I've been reloading for 35 years and have never seen a brand new piece of brass do this.
I figured I may have some how or another nicked the case mouth while loading up some horn. 140 gr.
So I pulled it and much to my surprise, I didn't. Upon inspection of the case, I could quickly see the culprit. You could see a discoloration on the inside of the case right where the Crack was.
Bummer! Seeing as how expensive nosler brass is? Wtf!
Oh well, alls not lost I figured hey....might as well use this case to see what my free bore is with my new 260 lrp and Hornady 140g match pills.
Need to give nosler a call though.

http://i182.photobucket.com/albums/x...psiwffcd4h.jpg