Not all of the data in Ackley's book is over the top. Some of the loads are actually mild to standard for various cartridges. That said, you have to be VERY careful with some of the data. All rifles are individuals, and loads that are smoking hot in one might be fine in another. The advice to start at 6.5x55 levels and work up is very sound, although I wouldn't start at the max load even then.
The 6.5x55 improved arch data corresponds pretty well with what several users of the 6.5/257 Roberts Ackley Improved (.260AAR) have reported to me during load sharing and correspondence. The .260AAR has a little more powder capacity than the Arch version, but the gain for the improved 6.5x55 over the standard version will probably be about 60 fps when loaded to the SAME pressures. When the chronograph shows a 60 fps gain over the max loads for the 6.5x55, it is time to stop.
The 6.5 improved rounds are lots of fun, but there is no magic in the case capacity/potential velocity relationship.
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