need help with manufacturing

[dreamer1]

Hi boys!
I am working on project that is about building a muzzle loading large calibre gun that fires lead bullets. The calibre is 13mm and the length of the gun is about 17cm. I have a question about how the grooving should be done.

1) What twist rate should there be? 3 turn 4 turns?

2) What direction should the grooves turn, right or left?

3) How many grooves should there be, and how wide should they be? For example 12 grooves each groove with the length of 0.4millimetre

4) How deep should the grooves be, for example 0.4millimetre?

And finally what are you basing your answers based on?

Thanks a lot guys.

 

[Jim Watson]

I have looked up two established barrel makers' specifications.

Green Mountain muzzleloader barrels are made to the following specifications
Each barrel has eight lands and grooves.
Grooves cut .010 to .012” deep, depending on caliber.
Twist is 1 turn in 48 inches for .32, .36, .40 caliber.
Twist is 1 turn in 60 inches for .45 caliber .
Twist is 1 turn in 70 inches for .50, .54, .58 caliber.

Rice barrels are made to these specifications
Each barrel has 7 lands and grooves for .50, .54, .58, and .62 caliber.
Grooves cut .016" deep, with round bottom rifling.
Twist is 1 turn in 66 inches for 50, and .54 caliber.
Twist is 1 turn in 72 inches for .58, and .62 caliber.

They are intended for patched round balls in rifles. A lightly loaded target or dueling pistol with concealed rifling would likely have a faster twist for low velocity round ball but I have no data on just what it should be.
Edit to add: Pedersoli uses a twist of one turn in 18" in the Mang target pistol for round ball at low velocity.

If you wish to use cylindro-conical bullets, the rifling twist must be faster, look up the Greenhill formula.
If you wish to use a lubricated naked lead bullet, the rifling grooves can be shallower.
If you wish to use a paper patched bullet, the rifling grooves can be shallower yet.

If you are making your own barrel and wish to reduce the labor, you can get away with fewer grooves, Springfield and Enfield rifle muskets used three groove barrels.

Direction of twist has no significance.

 

[CypherNinja]

2) What direction should the grooves turn, right or left?

Left works better in the Southern Hemisphere, up here you should use right.


LOL

 

[Jim Watson]

That would be news to Colt.

 

[dreamer1]

I don't get it

I have looked up two established barrel makers' specifications.

Green Mountain muzzleloader barrels are made to the following specifications
Each barrel has eight lands and grooves.
Grooves cut .010 to .012” deep, depending on caliber.
Twist is 1 turn in 48 inches for .32, .36, .40 caliber.
Twist is 1 turn in 60 inches for .45 caliber .
Twist is 1 turn in 70 inches for .50, .54, .58 caliber.

Rice barrels are made to these specifications
Each barrel has 7 lands and grooves for .50, .54, .58, and .62 caliber.
Grooves cut .016" deep, with round bottom rifling.
Twist is 1 turn in 66 inches for 50, and .54 caliber.
Twist is 1 turn in 72 inches for .58, and .62 caliber.

They are intended for patched round balls in rifles. A lightly loaded target or dueling pistol with concealed rifling would likely have a faster twist for low velocity round ball but I have no data on just what it should be.
Edit to add: Pedersoli uses a twist of one turn in 18" in the Mang target pistol for round ball at low velocity.

If you wish to use cylindro-conical bullets, the rifling twist must be faster, look up the Greenhill formula.
If you wish to use a lubricated naked lead bullet, the rifling grooves can be shallower.
If you wish to use a paper patched bullet, the rifling grooves can be shallower yet.

---

Thanks man!
Buy I still don't get it.
If one inch is 2.54cm then my barrel can't even have one twist, because
66 * 2.54 = 167.64cm, that’s more than 1meter and half, how could this be right?
If this is right how can regular handguns have several twists with short barrels that's not longer than


I also have some uncertainly about how deep the grooves should be in millimetres, how much is .012 in millimetres? If .45 is 11.43mm then we can translate one millimetre to .03937.. by 0.45/11.43=0.039..
0.012/0.03937 = 0.3.. millimetres is that right?

 

[Jim Watson]

There is no ballistic requirement for the rifling to complete a turn in the barrel. The twist RATE or "pitch" is all that matters. For example, if you have a 17 cm long barrel with the Pedersoli pistol twist of one turn in 45 cm; then the rifling will make only about 1/3 turn in the barrel. But the ball will be spinning and will keep spinning at the RATE of one revolution every 45 cm all the way to the target. That is enough for stability and accuracy.

At 25.4 mm per inch or 1 meter = 39.37"; for quick conversions just take 1mm = .04" approximately. Then the typical muzzleloader rifling depth of .010" to .016" is .25 to .40 mm.

 

[dreamer1]

Well how long should one twist be for my purpose, 45cm for one twist?
What about the width of the grooves? I don't mean the depth just the width is there any standard for the, because you can cut the grooves with different width.

 

[Jim Watson]

The 45 cm twist should be adequate, that is what Pedersoli uses in their .44 pistol barrels and is in the range of what is used in 19th century cartridge pistols. Green Mountain .45 pistol barrels have a 20 inch = 50 cm twist.

As to the width of the grooves, about every possible combination of land and groove width has been tried over the centuries. Green Mountain grooves appear to be about the same width as the lands or a bit narrower.
http://www.gmriflebarrel.com/catalog.aspx?catid=PistolBarrel1316Octagon