Groove To Land Width Ratio

[nkbj]

Are there any established rules on what ratios of land to groove widths are generally best for round ball and for lubed bullets?

 

[mattybock]

I'd doubt it, back in the old days the gunsmith made his own doo-dads, (reamers, drills, what have you). Seems as long as he had grooves in the barrel without extremes, it all turned out alright.

 

[longcruise]

Just my opinion, but I think narrow lands and wide grooves are best.

 

[Ken Rummer]

I agree. The narrow lands would make for easier loading by reducing the percent of the PRBs circumference that is deformed during loading.

There was a style of rifling that uses the narrow lands. I don't recall the name but Roundball mentioned it in several of his posts.

 

[zimmerstutzen]

Harry Pope made barrels with lands that were about an eighth the width of the grooves. His round grooves were cut with a cutter having a curve radius that was larger (x 2) than the bore radius. (most round groove rifling made for modern muzzle loaders uses a cutter with a much smaller radius curve than the bore) the result of pope's system was that the middle of the grooves was the same as land height, but the corners of the grooves were deeper along side the very narrow lands.

Alexander Henry, the British gun designer cut rifling that was more like a series of wide and narrow humps. He also made double choked rifle bores. choked ahead of the breech and again at the muzzle. The "grooves" actually look like raised humps. Sort of the opposite shape of round bottom rifling ie instead of concave it is convex with the corners along the lands being the deepest part. As i recall, the lands are about one fourth the width of the grooves.

 

[longcruise]

Maybe it's the Forsythe rifling??

 

[nkbj]

Actually the patch not being exposed to sharp machine cut edges makes a lot of sense. Perhaps I just learned something.

 

[Dphar]

Actually the patch not being exposed to sharp machine cut edges makes a lot of sense. Perhaps I just learned something.

"Sharp" is relative. A bore with raised burrs "wire edges" a friend calls them WILL cause problems. But having a nicely cut bore with nice square corners at the lands is not a problem.
Narrow lands load easier. I don't know the land groove ratio of my McLemore match rifle barrel but the lands are pretty narrow.
Speaking of Forsythe, he recommended very narrow lands we also have to remember that he probably was shooting rifles with 12 grooves or more.
This is a drawing from "The Gun and Its Developement" by W.W. Greener 1896 edition (there are many). Forsythe and all other heavy game hunters SFAIK shot hardened lead which will load easier in a barrel with narrow lands.
The typical American barrel of the time was Seven and these were often equal width many were even narrower. Some have little tiny grooves at the corners of the heptagonal bore.
This is a recut to 58 caliber 1803 Harpers Ferry.

This is a common land groove ratio in original guns as well. This being a 1814 Common Rifle

Or a round bore with little tiny grooves.
Personally I don't see how this rifle could have shot very well. Its from 1840 and is a cheap Leman "Connestoga Rifle Works" flintlock that was unfired.

Douglas used equal lands and grooves

This is a Green Mountain 58 still fouled after a proof shot.

These are GM 50s and appear about 2:1

This is a J&S Hawken from 1836

This appears to be common in Hawken rifles which had an excellent reputation for accuracy and is pretty close to the Douglas which shoots very well indeed.


Dan

 

[Dphar]

Here is the missing drawing from Greener. I hope..
For some reason the post photos thing is acting up today and nothing shows thought I had it all good but this one disappeared.... Darned devil box anyway.

 

[nkbj]

Greener's "Gun And It's Development" is an excellent resource. On the page over from that illustration begins a discussing of the .40 and .52 caliber hunting rifle developments in the 1850's using 1:30" two groove rifling with matching fins cast on the rear of the bullets. The conical illustrated is about three calibers in length. Doesn't say whether or not they used a card wad.
At the conclusion of the discussion there is an interesting statement: "Colonel G. Hanger, writing in 1814, contended that he had such a rifle as the Express; the secret of it's production he discovered in America, and that it might not fall into other hands he sawed his rifle barrel in half and threw the pieces into the Thames." If you can think of it, somebody's done it!