Just use Western Powders suggested charge for their 124/125 grain for AA#9 (11.7 - 13.0 grains and COL of 1.140"). The Xtremes can handle the velocity, I've run them at 1,450fps and they shoot fast, flat, and accurate. However for plinking I've backed off a tad to save on case life. I run em around 1,320fps now. Very accurate.
Edit: be careful on certain brand cases of running near max or max loads.. the AA#9 powder fills the case FULL and the compression from seating the bullets can bulge the shoulders and cause the rounds not to feed or chamber. Different cases have slightly different internal volumes. I've found this out using mixed headstamps.
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