Causes of Low pressure -223

[rsrocket1]

My remaining question is what should I key off of? Take the FPS to 2900 and stop OR wait for the rounds to show signs of overpressure?

None of the above. Start at 23g, work up and find the most accurate load at or below 25.3g. If you reach 25.3g and don't find anything satisfactory, try another powder or use the powder for close range plinking. The recommended max charge by Hodgdon for a 55g bullet is 25.3g so you should use that as your top hard stop. I'm pretty sure you should find an accuracy node within those 2 weights. In fact I think you should find 2 accuracy nodes within those limits.