I'm having the same problem, glad to see you've got yours figured out HANDLDR, going to switch brass for my next trip to the range and hope my problem goes away like yours did!
I bought a new 25-06 X-Bolt last fall, put a Leupold 3-9x VX-3 on it, and have spent a lot of money on powder and brass trying to get the thing to group, and haven't been able to get anything under 1.5" @ 100yds, with some groups up to 4". I've also used Hornady brass since the start, and the gun has always been properly cleaned and cared for. Tried 120gr Speer Grand Slams, 117gr Hornady BTSP, and 110gr Interbonds, with IMR4831 and H4831, all with no success. I bought this gun because I was so impressed my first X Bolt (300WSM) that will punch out clover leafs all day long, but have been very frustrated trying to get the 25-06 to shoot.
I'm pretty new to reloading... is there a way to correct neck tension problems, or are the cases basically garbage?