I went to the range again, and the results with Retumbo were just as dismal as before. No change in the very crappy accuracy. The best "group," if you want to call it that, was 6" across at 100 yards. Pathetic. But I've concluded that it's the powder to blame. I believe that, even with the heavy for caliber bullets, it is just too slow and isn't burning consistantly. I wish I had my chronograph fixed, because I suspect that the velocities would be all over the map. Retumbo's a bust in the 257 Roy (mine, anyway).
But the good news is that I also decided to split the remaining bullets I had on hand and try a ladder test with another powder I had on the shelf, Reloder 19. Now, my first thought was that it'd be too fast for the 257 Wby, and it probably IS on the fast side for 115 grain bullets, but I have some Quickload data for RL-19 and 115 grain bullets, and I have no current use for RL-19 (I used it when I had my 300 WSM), so I thought what the heck.
So I started the 13 shot ladder test at 59.6 grains and went up to the max of 62.0 grains. Seated the 115 grain Nosler BT's at 3.35" COAL, which is really long, but still nowhere near the rifling. In fact, I have no idea exactly how far off the lands the bullet is because the bullet falls out of the case before reaching the lands. LOTS of freebore.
So here is the raw target and the summary target I made from my range notes.
Point of aim was the center "X", but because I had been fiddling with the scope mounts, the initial group center was 3/4 high and 1" right. The scope was adjusted after shot#10 1 MOA (4 clicks) left and then shots 11-13 were fired.
Looks like I have a "node" with shots 1 through 3 (59.6 to 60.0 grains), then the groups opens up from shot #4 through #7 (60.2 thru 60.8 grains). Then it hits another node from #8 through #13 (61.0 to 62.0 grains). The "sweet spot" of the higher node seems to be #9 thru #11, so call the best load 61.4 grains, corresponding to shot #10. The Quickload velocity for 62 grains from the 26" bbl is predicted at 3,240 fps, and 3,099 fps for the 59 grains (I started a bit higher than the 59 grain starting load because my seating depth was 0.18" longer than the Quickload COAL). Based on this, and this is purely a guess without my chronograph, I would predict the MV in the 3,175-3,225 fps range. Not too shabby when the highest predicted velocities for the slower burning powders is in the 3,275-3,300fps range. It's a little slower than what's possible, but accuracy trumps speed every time as long as the speed is in the ballpark of the cartridges max performance. The difference in drop would only be 2.1" at 500 yards, which is nothing to sweat about.
Looks like I possibly found a load for this rifle after all.
Mike