Savage says the twist is 1-24" and I'm not very familiar with the types of crowns. I just shoot what's given to me. But the end of the barrel is flat all the way across.
I'm hoping to get out again soon with different loads. I'm going to try 20, 21, and 22 grains with the 250gr bullet. I'm hoping that my accuracy was blown because the velocity was too high (due to the condition of the sabots).
I'm not very familiar with the different powders and their characteristics. I looked at the different types online and compared the descriptions. Based on what I found, the best for higher velocities were Longshot, Blue Dot, and 800X. I've always reloaded Clays for trapshooting, so not much off hand knowledge. I've heard that Longshot is cleaner than Blue Dot from several people (including you), but when I looked down the barrel after shooting 9 shots, there was a lot of unburned powder and things were dirty. So based on that, from my experiences, that means too much powder.
I'll keep trying. If I don't find a good combo with the Longshot, I'll try Blue Dot or 800X. I'm having fun finding out what works and what doesn't. So far I've found out what doesn't.