In the world of AR's, I know 1:9 is supposed to be ideal for 55gr, so I wouldn't think the twist rate should be an issue there. I also know 55gr are pretty inaccurate compared to the heavier bullets. I would try 62gr and heavier when you get the chance before you start getting worried. My AR with an 18" 1:8 heavy barrel groups very poorly with the 55gr, but shoots half-moa with 77gr sierra bthp.
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