Ted,
Regardless of the twist rate, which you can easily figure out with a cleaning rod once you have the rifle in hand, there will be several choices open to you that should work well out to 1000 yd. As mentioned, the Berger 155s, but I also wouldn't rule out Berger 168s, or the 175 gr Tactical bullet. Both of those have a higher G7 BC than the 155 Hybrid. Each of my GAP .308 rifles have .085 freebore, which is identical to the Obermeyer default chamber FB as Monte mentioned above. As you have seen, those rifles absolutely love the Berger 175 Tactical bullet. They also shoot extremely well with JLK 180s, which are loaded for me to just a tick under 2850 fps (out of a 28" barrel) by Andrew McCourt. The JLK 180s are fairly close in dimensions to the 185 Juggernauts, so with a little luck, you may well be able to get the 185s to work. Either way, you'll have several options that should be suitable for your chamber/barrel and ought to get you good results at 1000 yd. If you're going to be at Pendleton for the MR match in a couple weeks, we can talk some more about it.