Twist rates v powder charge

[Wes/Tex]

Exactly...the rifling depth is far more important than actual twist rate. The knock against 1-48" twist got started back in the 60's when we first got Zouave rifles from Zoli and groups were here, there and yonder. In the end it wasn't the twist rate at all, it was the very shallow groove depth of .003" and the fact that there were were only 3 each grooves and lands of equal width...1/6th of the bore diameter. Just perfect for Minie balls but a PITA for patched balls. We eventually discovered decent groups were possible with tight ball/patch combos and moderate charges. Last I heard, Zoli and others are now cutting the grooves to .006"...still shallow for patched ball but better.

The Hawken boys did use 1-48' twist, but as Gus said above, that's what they had. Their 7 groove rifling cut .010" to .012" was designed for patched ball, and worked great. The 1-48" twist got a bad rap due to problems that didn't include it's actual spin and the old prejudices still hang on.

 

[George]

An article regarding an inspection of the rifling machine from the original Hawken Shop in St. Louis which ended up in the possession of the Missouri Historic Society.

Bulletin #7 (Spring 1963) from the American Society of Arms Collectors, "ST. LOUIS GUNS, THE MECHANICS OF MANUFACTURE AND POINTS OF IDENTIFICATION", by Dr. Byrne and Clarence B. Fall ”“ NFI)
http://americansocietyofarmscollectors.org/wp-content/uploads/2013/03/B007_Fall.pdf

Some remarks from the article;

We found this rig complete and in fine condition although it shows much use. It is typical in design except much more metal was used.
It is approximately 10 feet long.
The threaded feed screw is metal with male threads, right twist. It can’t make a left-twist groove.
The indexor will permit a 7 land and groove cut.
The cutter mounted in the wood bore fitting plug has a slight curvature to produce rounded bottom grooves.

(The author notes ”“ from slugging original barrels - “All observed Hawken long guns have 7 lands and grooves with the grooves having a noticeable rounded bottom or curvature. They are all right twist. Approximately one turn in 48.”)

Study of the machine showed rifling with 6 and 8 grooves was possible, maybe others.

Spence

 

[Zonie]

Although 6 or 8 groove rifling may have been possible, it would not have been practical.

The single tooth rifling cutter needed a good, solid surface directly opposite the tooth to support the cutter. This could only be provided by the bore.

If an even number of rifling grooves were used, after half of the rifling grooves had been cut a groove would have been directly opposite the cutting tooth. This would provide less support and chattering would likely be the result.

This "odd number of rifling grooves" is one of the things people look for to determine if the barrel on antique rifles is original or if it had been made more recently, when multiple rifling groove, broach style cutters were available.

If the bore has an even number of grooves, it is very likely a newly rifled barrel.

 

[M. De Land]

I would say rifling .008 -.010 deep would be optimum and with radiused corners.
Deep rifling is not a panacea in or by itself when all that is needed is enough to not allow the patch or ball to slip in the bore. Any deeper grooving is only a fouling trap filling up with each shot. Wiping between shots rubs off the top of the fouling for a while but it still is increasing with each shot.
Also tighter rifling pitch increases fouling build up.
The idea is to get enough grip on the patched ball to not slip and have enough pitch to stabilize the ball with rifling depth enough to take some fouling build up without tearing the patch for a balanced compromise of the best load virtues.
Also, very deep rifling needs thicker patching to seal off the gas.
Cloth patches usually need to be over .015 thick to have enough strength not to tear and tight weave enough to seal properly.
Actually the best patch thickness I have ever used is .022.

 

[M. De Land]

Jim, the grooves are not generally individually cut to final depth in single point cut rifling.
The cutter depth is shimmed to height indexed to each new groove until it stops cutting all the way around the bore and then is withdrawn to be shimmed higher for the next series.
An interesting aside is that the cutter cuts more shallow at both ends of the bore as the cutting head moves up bore from support on the front side of the box to support on both sides (fore and aft)of the hook or scraper as it inters and again as it exits the bore.
This can be used to good advantage at the muzzle for a bit of choke in the groove bottom.
Gain twist rifling scrapers or hooks cut a gradually wider groove as the pitch increases.

 

[M. De Land]

For a ball rotation RPM lets for ease of figuring use a 1 in 60 pitch.
The ball makes 1/5th of a rotation per foot of bore travel.
.20 x 1800 fps(muzzle velocity) for a .50 cal = 360 revolutions per second x 60 = a ball RPM of 21,600.

 

[M. De Land]

I have come to the idea of fitting the ball diameter to the patch thickness rather than the patch to the ball which is the usual way of doing things.
Once one finds a close weave, tough, reliable patch material that can be obtained regularly then finding a ball diameter that best fits the bore of your rifle is all that needs to be accomplished for repeatable accuracy.

 

[M. De Land]

Interesting because 90grains of 2F Goex is my accuracy load in a .54 cal Douglas barreled Hawken style rifle.

 

[Rifleman1776]

This "odd number of rifling grooves" is one of the things people look for to determine if the barrel on antique rifles is original or if it had been made more recently, when multiple rifling groove, broach style cutters were available.

If the bore has an even number of grooves, it is very likely a newly rifled barrel.

As long as I have been at this game, I'm still learning. That is good info and, really, should be self-evident. Thanks. :thumbsup:

 

[M. De Land]

I don't know about uneven numbered rifling being a sign of how old a rifle is because single point cut or scrape riling is just as accurately and easily accomplished in even as odd numbered rifling. The notion that the cutter has to have a land directly opposite it, on the back side to cut an accurate groove is just not correct.
Odd numbered rifling may have some advantage in bullet obturation support according to British thinking.
Early rifling was all single point and the cutter was called a "Saw". It worked like a single tooth broach but cut in both directions.
Broach cut rifling is a modern, one direction technique as it takes hydraulics to pull the broach which cuts all the grooves simultaneously. Each row of teeth around the broach is progressively taller. The broach doesn't care either wither it's odd or even numbered rifling.

 

[M. De Land]

It worked like a "single groove" not tooth, broach having several teeth on a slight tangent, in a row.

 

[Newtire]

For what it's worth, GreenMountain used a 1:48 twist for their .32, .36 and .40 caliber round ball barrels.

Colerain uses a 1:48 twist for their .32 thru .45 caliber round ball barrels.

At one time, Track of the Wolf offered York Rifle Barrels. The .32 thru .40 caliber roundball barrels had a 1:48 twist.
York Barrels was the successors to the Green River Rifle Works of Roosevelt Utah.

Since you are interested in a small caliber roundball barrel, I figured you might be interested in what twist some of the better known barrel companies used.

I have a rifle that belonged to my Great Grandpa. It is a 17-1/2 lb. target rifle with a barrel that’s marked Remington Cast Steel. It’s a .40 caliber with 1-48” rifling. I don’t know who rifled it but I wound up fleshing out the rifling with a cutter a machinist showed me how to make. It shoots real well and loads real smooth now that the rust is all gone from the grooves. This gun was made around 1850 by a gunsmith named G. Spangler out of Monroe, Wisconsin. But, like you say, 1 turn every 4 ft. seems to work for it. It came with a Pickett mold and is turned round for maybe a false muzzle. Otherwise, I don’t know how you would get the bullet started straight. I just shoot round balls out of it but now have a few hollow based .40 cal. Molds to try. Too many guns, not enough time...