A 9 twist will handle up to 69gr bullets, some 75s but that may be pushing it.
The 556 and Wylde have longer throats and will handle full power M193 or M855 loadings. A 223 chamber throat may be too short and cause excess pressure.
The 6.8 is the fastest growing cartridge and #1 choice for hunting deer and hogs with an AR15.
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