I would think that 1x7 would be too fast for 40-45gr due to their rotational velocity, but should be fine for 55gr and up.
This has been my experience - I have a 14.5" and a 16" both in 1/7 twist - 55gr are fine (though I haven't tried any 45gr - I didn't even know there were 40gr .223 rounds out there).