You probably read one of my posts on this subject. 20x47L was a fail with a 9 twist krieger, yes by a little less than 300 rounds the 55's were smoking, giving comet trails on paper, and a generous portion not making it to the target. I complained to Krieger and they wouldn't replace the barrel. Fortunately 40 vmax work at 4100 fps??? but I haven't used that barrel in a few years. Included in my goal for 20x47L was using it with 10 round AI mags, that part worked. I still have all the reloading stuff so if I do one again I'll try a 10 twist as well.