Your rifle probably has a 1-9" twist rate which is not good for 40 grain bullets. If your reloading then there are powder options available too help in accuracy department. My rifles group better with 50 grain bullets using the 1-9" twist barrel as do my AR with same twist. Older rifles with the 1-12" twist rate tend too shoot very well with either weight bullet. Some will tolerate the faster twist with lighter bullets but my experience is the group accuracy opens up.
Don't know what type of problems your having that leaves low impression of the 223. My experiences tend too limit the caliber in range too 300 yards shooting varmits. That would be marginal on coyotes where the 22-250 or 243 would be a better choice at that yardage.
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