It is a solid base bullet, but it has a very slight bevel on the bottom edge. I picked out the ones that were the cleanest, because a lot of them had extra lead junk on the bevel. I know that the base and especially the boat tail portion if damaged can cause inaccuracy, but I don't think that it can cause 18-in group inaccuracy.
I think I agree with you on the speed. I did a little bit of searching and found some suggestions of it being velocity related when it is near the muzzle. Or maybe it could be that the bullet has run out of lube at that point. On MBCs website, I'm pretty sure I read that this bullet should be good up to about 1,800 ft per second. That load data is actually for a 29 inch barrel. My barrel being a 24 inch barrel, I would think that I wouldn't be any higher than 1,500 or 1600 ft per second. Then again, I'll have to be careful with how low I go in speed, because in 18 bhn bullet might not seal the barrel soon enough if the charge is super low.
I don't have a bullet puller. Would the cheap inertia hammer style bullet puller you see it most stores be sufficient to get these bullets out?
I think on the next go around, I'm going to work up some charges just below the recommended starting charge and work up to the lower starting charge. I might also make up some of the same charges I shot today and put a greased up wool felt wad behind the bullet to see if that makes any difference.
I'm also going to shoot at the 50 yard range, because it is dang hard trying to work up an accuracy load at 100 yards with regular iron sights.