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I'm having a hard time reconciling the two images, Kraigwy's comparison of M193 and M855 target impacts and JonnKSa's "223REM rifling vs accuracy by bullet weight" and other graphs of his that indicate that 1:12 should be fine with 62gr bullets.
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There is a critical caveat in my post.
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Bullets made of solid copper (or gilding metal or bronze), or bullets with steel cores will be longer for a given weight since those metals are less dense than lead. Because of their additional length, they might not stabilize with the twists recommended for a conventional (copper-jacketed lead core) bullet of the same weight.
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The 62 grain ammunition Kraigwy is referring to has a steel core.
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If I could use 62gr, that opens up more opportunities for ammo.
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With a 20" barrel, and out to a couple hundred yards, you're probably fine with 62gr ammo as long as it uses conventional copper-jacketed lead bullets and not solid gilding metal/solid copper or steel core bullets.
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Do you have a link to the articles ?
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No, the articles are not online. I entered the data by hand into a spreadsheet to make the plots. You can probably contact the two magazines in question and ask for back issues or article reprints.
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As we know 223 does not have the same velocity as 5.56.
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The velocity difference due to caliber is almost certainly swamped by differences from one gun to another and IS certainly swamped by barrel length differences.
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More powder means more pressure...
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All else being equal it does. There are other differences in the two cartridges, the main one being the throat length which can have a significant effect on pressure.
Here's a fairly thorough treatment of the .223 vs. 5.56 issue.
http://thefiringline.com/forums/showthread.php?t=530912