This is good, but I would start with a 55g since they are more common. I have had very good results in a 1:8 and a 1:9 barrel with a 55g. The 1:9 does not like the 69g. Mine were only 16" barrels, your 24" should be able to stabilize almost anything you can run through it.1:8 twist should be able to handle from 55gr to 72gr without a problem. You will just have to experiment to see which one gives the best accuracy. I would start with 62gr.