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@scsov509, The trend as the rate of twist is going to be as you say. The magnitude is another question. Assuming my freshman physics and integral calculus is right, adding a typical twist makes a small negative correction to the velocity that is proportional to the twist squared times the radius of the bullet squared. Since the number of turns per inch of the twist and the radius of the bullet in inches are pretty small numbers, your meter might not be able to detect the change.
In which case what I said about velocity is correct but kind of irrelevant.

Interesting. Given the math you propose, I wonder if you'd be able to see a more substantial difference comparing twists in a larger caliber where you've got a larger diameter? The physics and math make total sense, I'm just curious to see if it actually translates into an appreciable difference in a rifle.
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It seems (and I'm learning here) that if I wanted to strictly target shoot with 55gr, I would be better off with a 1:12 rather than having a more versatile option with the 1:7.

I personally would never go slower than 1:9 in a 223 barrel unless you were planning to shoot a lot of lightweight varmint bullets. The 1:9's will shoot a pretty wide range of bullets quite well, whereas the 1:12 or 1:14's limit you to smaller bullets. So I think that a 1:9 is the best all around twist if you want the widest range of options. But if you don't ever plan on shooting light, thinly jacketed varmint bullets then a 1:8 or 1:7 is even better since you can shoot all but those varmint bullets fairly well.