What kind of rifle are you shooting? I have done a bunch of cast bullet shooting with a M96 Mauser, using the 150 gr. Lyman bore rider. This rifle has an extremely fast rate of twist - 1:7", and as a result works well at fairly low velocity, but bullets come apart if you lean on them much at all. Best loads for me were with IMR4227, in the 1500 fps range. It worked well up to 1700 or so, then totally went away. Many powders work well in the 6.5X55, but my particular rifle liked 4227 best. If you have a commercial sporter with a more usual 1:9, you should be able to load a little hotter with good results.