the twist rate im working with is 1:7, not sure how effective that powder you listed would be with +55gr.
As others have noted, you will likely find several powders that work. I have had good success starting with minimum loads and working up. Sometimes the maximum load is most accurate in MY RIFLE and sometimes lighter loads are more accurate. I'll sacrifice some speed for accuracy. You may want to do something else.
As far as buying from other Calguns members is concerned, I've had nothing but good experiences with bullets and cases. Those transactions weren't always at the lowest possible prices but they were close enough and at the time of the transaction, particularly with cases, I could find what I wanted here and nowhere else. I have to keep reminding myself that sometimes it's better to pay a little more in the short run to avoid paying a lot more in the long run.

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