Barrel-makers use this "rule of thumb" for land and groove widths:
<br>25% of the circumference of the bore in lands
<br>75% of the circumference of the bore in grooves
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<br>The lands in a six-groove 0.224 barrel are therefore narrower than the lands in a six-groove 0.308 barrel, which in turn are narrower than the lands in a six-groove 0.358 barrel.
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<br>The lands in my three-groove .220 Howell barrels are therefore twice as wide as they'd be in a six-groove 0.224 barrel.
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<br>Land height (groove depth), IIRC, is essentially the same in all.
