Yeah, I looked in to getting my wife a .223 bolt gun and was disappointed by the twist rates offered.
They tend to market towards light weight varmint shooters.
What is the rifle model?
Are we talking Remington 700, Savage 10, Rossi single shot break over?
I would think that 1moa would be accurate enough to take any varmint out to the effective range of the .223.
I have shot many crows and groundhogs with a rifle that would do about 1moa.
I think that most of the 1/2 moa groups people talk about on the forums were shot with the keyboard.
You have a 1 in 9 barrel, but how long is it? A heavier than 55gr bullet in a 16" will probably lose accuracy, however if you have say a 22" barrel then you may be able to pull it off.
What else have you tested? I assume you are a reloader given the pic above. How are you going about load development? Are you only using one powder type?
Texas doesn't allow rimfire for game animals, no restriction for varmints.