Home Forums Hunting & Shooting Ask The Gunwriters Standard land/groove measurements

If anyone has information, diagrams, etc., of the standard/common land/groove dimensions for various calibers could they post or e-mail the information?
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<br>Are these dimensions fairly standard between barrel manufactures, or are there large variations?
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<br>Dr. Howell, if I remember from long ago on another board, you may have used the Quick load software for at least partial development of you Howell line of cartridges. Does that software contain the information?
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360BE
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<br>I happen to have a SAAMI book (Centerfire Rifle eddition) here at my desk. What would you like to know?
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<br>Good hunting,
<br>Dale (M70)

Dale,
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<br>Land width, land to land diameter, and groove to groove diameter. If there is a standard for each, and time allows, calibers .223 � .458. If not, I am most interested in the .358 measurements.
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<br>Where did you get your SAAMI book?
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<br>Thanks,
<br>360BE
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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.

Ken,
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<br>Thanks for the help.
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<br>As a follow up, what are the benefits/drawbacks of more or less lands/grooves? Do the wider lands grip better at higher velocities or with faster twist rate barrels? You commented that you have a three-groove barrel on your .220 Howell. Do certain calibers (larger vs. smaller) realize greater benefit from more or less lands/grooves?
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The smaller the bore, the narrower its lands. The lands in a six-groove .224 are only half the width of those in a three-groove barrel -- very narrow indeed, thus more easily and rapidly worn.
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<br>The circumference of a .224 bore is 0.703 inch. -- 25% of this in lands would be 0.176, making each of six lands only 0.0293 inch wide or each of only three lands twice as wide (0.059 inch).
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<br>The three-groove barrel has fewer sharp land corners to score (deform) the bullet jacket and fewer groove corners to collect heavy fouling -- only half as many as the corresponding corners in a six-groove barrel.

A couple of additional points may be added.
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<br>When doubling the diameter, the area actually quadruples. Thus going from .22 caliber to .44 caliber isn't twice the area. It is four times.
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<br>As regards standards, ( covering 150 years ) one has to wonder if people in the gun industry have ever standardized on anything? Old military weapons had two riflings. Then there are riflings in a variety of numbers on up to 8 and beyond in the "micro grooves".
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<br>In generic terms a .30 caliber gun shoots .308" bullets. Thus, on the face of it, one could easily extract the difference ( .308" - .300" = .08" ) Divide by two and the height is .04". But that isnt alway the case. In fact, in the published listings of calibers, some that are stated are not the actual caliber at all. And some calibers that are thought of as standard vary by thousandths from one nomenclature to another.
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<br>A .218 bee is .224"
<br>A .219 Zipper is .224"
<br>A .22 Benchrest is .224"
<br>A .22 Marshburn is .228"
<br>A .22 Remington Jet is .223"
<br>A .224 Weatherby is .224"
<br>A .225 Winchester is .224"
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<br>Sometimes it pays to slug a barrel.
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<br>Bill Tibbe