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Longknife
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20 bore rifle twist
      #361746 - 10/02/22 10:11 AM

I am looking for advise on 20 bore rifle barrel specs. Say I want to shoot a .620 X .630 bullet over a black powder load and hope to get it in the 1300 FPS range. (see link) What would be the ideal twist? I know what the online twist calculators say but does anyone have any real experience with something like this? Thanks, Ed

Accurate mold

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Longknife


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DarylS
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Re: 20 bore rifle twist [Re: Longknife]
      #361752 - 10/02/22 11:57 AM

Hi Ed - No real experience, but that short a bullet would stabilize in a 48" rate of twist at that velocity. That isn't much bigger than .58 & the US mil. did fairly well with 72", although the British 2-band rifles were more accurate with their 48" ROT.
Likely anywhere from 30" to 50" would likely work well with that stubby bullet. Closer to 50" would also shoot round ball at a decent vel.
Taylor's 16 bore Joseph Lang shoots RB well with it's 48" twist.

Buidling a DR?

--------------------
Daryl


"a gun without hammers is like a Spaniel without ears" King George V


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szihn
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Re: 20 bore rifle twist [Re: DarylS]
      #361827 - 11/02/22 12:10 PM

I make muzzleloader for my living and I was a barrel maker at one time too. I still earn my living making muzzleloaders but no longer make my own barrels. But I do understand these things pretty well.

There are "formulas" that give you mathematical calculation for twists, but from experience and just looking at that bullet I would make twist 1 turn in 38" and I would cut the barrel grooves .004" deep. You will find that if you cut grooves 1.5 times wider then lands and .004 deep the accuracy will be very good. Some rounding of the corners at tops and bottoms of the lands and grooves both is helpful in such barrels. Sharp corners do OK and can be very accurate, but if you are going to pick up lead in such bores it's common for it to gather on the corners first, so having a bit of rounding eases that propensity.

If making a muzzleloader it's best to have the your top land of the mold cut .001" over groove diameter so it engraves on loading and the rest of the shank of the bullet cut 001 under land diameter. It gives enough drag to keep the bullet against the powder when hunting.

If making a breach loader, make the bullet drop at groove diameter.

With a 1-38" twist you will be able to run powder charges giving velocities from about 900 FPS up to about 1800 FPS with good accuracy. Faster speeds will need a stronger alloy however.


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Longknife
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Reged: 17/04/08
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Re: 20 bore rifle twist [Re: szihn]
      #361841 - 12/02/22 02:22 AM

Daryl, I have been thinning the herd lately and need to either get some projects done or move them on. I have doner guns for a single shot and a SXS....

Steve. WOW. 1-38, that caught me off guard. That is the twist The Gun Works uses in their 62 cal English sporting rifles, but they shoot a much longer and heavier bullet. Smokeless slug guns also use twists in the 1=30 range. When I put my bullet in one of the online calculators it comes out as 1-72 and I was sure I wanted a faster twist than that. I was thinking as fast as 1-48 might be good, as Darly suggested, and work for round balls too. I can order that mold in .628 dia. too. Do you know a barrel maker that would make such a barrel? ? Thanks for the replies,,,,Ed

Edited by Longknife (12/02/22 02:31 AM)


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DarylS
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Re: 20 bore rifle twist [Re: Longknife]
      #361854 - 12/02/22 04:40 AM

Ed, have you checked Bobby Hoyte? I would expect either Ed Rayle (who currently has a 3 year back-log I read somewhere) or Bobby might be the only ones who would custom make one, but perhaps Badger Barrels would too.

38" twist should work, as Steve notes & might be better overall, but would not admit much of a round ball load. I have to agree with the .004" depth, to about .006" max. Top band at 2 thou. over bore size might be best, in my opinion, with the rest running bore size.

The grease grooves need to be larger and deeper and square, imho. More lube is needed for grease groove bullets due to the fouling. You don't want to have to wipe between shots, for a hunting rifle.

Speaking of which, for NA, a .62 RB is all that is needed, however making up a single shot for slugs has always been on the back burner in my mind.

--------------------
Daryl


"a gun without hammers is like a Spaniel without ears" King George V


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szihn
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Re: 20 bore rifle twist [Re: DarylS]
      #361861 - 12/02/22 05:56 AM

Yes I'd use the 1-38 because the longer twist will work with a short bullet like that, but the faster twist allows for a LOT more leeway on velocities. Revolutions per second around the circumference of the bullet is what gives it stability. (Diameter X pi) The idea is that at a given velocity the RPS around the bullet's middle will be "X" and the slower it goes forward, the slower it revolves. So a faster RPS at a slower speed means you get good stability at low speeds as well as high speeds, but you will find a 1-38 with .004" deep grooves and those grooves a bit wider then lands will grab the bullet well even when you fire it with a large charge of powder. Such a barrel will shoot tight groups with 70 grains of powder and also for 150 grains of powder, as long as the quality is good.

As I said, there are mathematical formulas that give you equations, but in my experience, such figures don't tell the whole story. A man with a rifle often wants to be able to use lesser powder charges and that means slower RPS which can open up the groups. But a faster RPS at a slow speeds hurts nothing.

When I was making my own barrel I did a lot of experimentation on this very subject. I made barrels as fast as 1-26 and fired ball in them and compared accuracy to those I made with 1-76 twist, and I found NO difference at all in accuracy. NONE!

What made a difference was rifling geometry. Wider grooves help a lot. You can't get too narrow for bullet guns so I recommend 1.5 times as wide as the lands for lead to steel fit. In guns that are used with cloth patches I found up to 3 to 1 ratio was very good. Slow twists do help to keep fouling down. A fast twist needs to be wiped a lot more often. But bullet guns need only a quick wipe if loaded from the muzzle. Breach loaders need good lube and a wad to carry lube and soften the fouling, but as long as the fouling is soft one bullet will "squeegee" the fouling from the previous shot.

Just keep in mind, the grooves of the bore become the lands of the bullet. The lands of the bullet need to be strong to resist the force imposed on them without stripping or smearing. Wide grooves in the barrel make wide lands on the bullet and wide lands are MUCH stronger then narrow ones.

The geometry and overall quality of the bore,and smoothness of the tops of the lands make a difference, but contrary to what is written and re-written over and over and over, what I have found to be the least important factor in making barrels for black-powder guns is twist rate. I do NOT say it makes no difference at all, but of all the factors in tool making for the cutting of the rifling, twist was the one at the bottom of the list.
It's on the list, but it's the last thing to worry about.

Edited by szihn (12/02/22 06:09 AM)


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DarylS
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Re: 20 bore rifle twist [Re: szihn]
      #361868 - 12/02/22 06:50 AM

No arguments from me.
I had a 38" twist .50 cal. Bauska barrel that gave me MOA at 100 yards, using aperture sights fore and aft. The rifling was .008" and I mechanically fitted the 450gr. bullets (Lyman mould)by forcing them through a die I made from a piece of the barrel. Seems to me, the rifling was equal width, lands and grooves. After lubing, they were placed in a yellow Flambeau loading tray.

--------------------
Daryl


"a gun without hammers is like a Spaniel without ears" King George V


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Longknife
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Re: 20 bore rifle twist [Re: DarylS]
      #361957 - 13/02/22 11:53 PM

Daryl, I was wondering about those shallow grease groves too. Accurate mold will make custom molds too, all you have to do is submit a design with measurements. Deepening the grooves will lighten the bullet a little but I could also lengthen the bullet a to keep it closer to one ounce. Also, its not uncommon to use grease cookies in BPCR's, I bet they would work here too.

Steve, Thats a great Synopsis of barrel making! I think you talked me into it, 1-38 it will be!!!, I do like that I will be able use a variety of charges and retain accuracy. Now to find a barrel maker! Thanks, Ed

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Longknife


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szihn
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Re: 20 bore rifle twist [Re: Longknife]
      #361964 - 14/02/22 03:06 AM

Oregon Barrels was owned my Joe Williams and he'd do any set of specs you want. He died 2 years ago, but I think the business survived and is being run by his old machinists and overseen by his widow Susie. Springfield, Oregon 97477
Phone: (541) 741-4118

Ed Rayl also can do what ever you want. Inside and outside. He's in Gassaway West Va. He has a very deep back-log and some times you'll need to wait for a while, but his barrels are always good. 304-364-8269.

Remember to tell them you want grooves wider then lands. The geometry is far more important then the twist of the rifling for any bullet that's not very long. Twist starts to become more important when a bullet is about 2.5 to 4.5 times longer then it is wide. In other words on a 62 cal gun your bullets will necessitate a tighter twist when they are 2" to 3" long. Such a bullet would be 1200 to 2300 grains. (that may kick some....don't-cha think) A .600-.620 bullet of about 1100 grains and moving at 2000 FPS would be best served with a 1-22" twist. But a 600 Nitro Express shoots "only" a 900 grain bullet at "only" 1900 FPS, so that will give you an idea of what the recoil would be like.

The bullet you show has no such problems inherent to it's use.

That bullet going anywhere from 800 to 1800 FPS is going to be very effective and with a 1-38 twist should shoot quite well at any practical range. My guess is that it will weigh in the 340 to 385 grain range. 1-38" is a bit of "over-twist" for it at 1400 FPS and higher, but when going under 1200 FPS it would be quite easy on the shoulder and still very deadly. So the idea of a bit faster twist then needed is to have the ability to shoot it at 45 ACP speeds with excellent accuracy and still be able to load it up to be a "moose flattener' when needed, with no loss of that accuracy.

I have been hunting and killing game from deer to buffalo and moose with a 62 cal flintlock since 1994 and I use a cast round ball shot at $1700 FPS and so far I have never recovered a ball from any animal except the buffalo, and even that one went from mid body to the skin on the neck of the other side. Such large projectiles work very well on game. Even my moose had a wound that went clear through and exited.

As a side note; does anyone out there want to own a 66 cal (16 bore) Rigby style rifle? I made this one for a man several years ago and his health has failed enough that he needs to sell his hunting rifles. It comes with a ball mold and has been very accurate. It is rifles in Forsyth style and has a slow twist so it's not made to shoot light loads. The sights were set to give a 75 yard zero (as I recall) and the load is 165 grains of 3f if memory serves. He's asking $3400. If interested let me know.
Tm 16 bore with peep 2 by
Steve Zihn, on Flickr
TM 16 bore with Peep by Steve Zihn, on Flickr
TM Rigby 12 by Steve Zihn, on Flickr
TM Rigby 5 by Steve Zihn, on Flickr
I made this rifle fist with a set of sights on the barrel but later he asked me to replace the rear with the peep sight. So that's why you'll see the older irons on the barrel in the bottome picture.

Edited by szihn (14/02/22 03:28 AM)


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Longknife
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Re: 20 bore rifle twist [Re: szihn]
      #361965 - 14/02/22 03:40 AM

Steve. The pictured bullet actually weighs 425 grains in WW. lead. I may modify it and have the grooves cut a little deeper for more lube, and then lengthen it to keep it closer to one ounce. I can also modify to .628 to fit the depth of the .004 rifling. Still be good at 1-35? Trying to figure out the weight after mods might be difficult.... Ed

Edited by Longknife (14/02/22 03:42 AM)


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DarylS
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Re: 20 bore rifle twist [Re: Longknife]
      #361970 - 14/02/22 05:01 AM

A groove diameter bullet is too large, imho. You won't be able to load it from the muzzle unless it is mechanically fitted first, or you use a false muzzle or bullet starter fitted onto the muzzle as with the Remington barrels of the 1800's.
As Steve stated, graduated band diameter would be best, as with the Lee R.E.A.L. bullets. Then, the conical would slug up to fit the rifling. Shallow rifling might not be best with round ball, unless very slow rate of twist. The slower to a point, the better.
A Lee style bullet with narrow bands would be easiest loading, but should have a flatter nose for hunting. If in the 400 to 450gr. range, should work on all NA game.
Shooting slugs in muzzleloading barrels never really caught on for hunting rifles (for dangerous game) as a very soft bullet of an expanding type needed to be used. Hardened round balls were found to give superior penetration compared to soft conicals of the day.
Conicals did however, become preferred when used in the early breech loaders as hardened conicals could then be used. This occurred after the actions became capable of handling heavy charges of powder combined with the conicals.

--------------------
Daryl


"a gun without hammers is like a Spaniel without ears" King George V


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Longknife
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Re: 20 bore rifle twist [Re: DarylS]
      #361976 - 14/02/22 06:42 AM

Daryl , This is going to be a breechloader. I'm loading in shotgun shells. I guess I didn't make that clear!

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Longknife


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szihn
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Re: 20 bore rifle twist [Re: DarylS]
      #361977 - 14/02/22 06:56 AM

Longknife, if you make mods to the bullet I also would opt for a slug with a flatter nose like Datyl S says. In fact, I would agree with his entire post.
A 1-38 or a 1-35 will be fine. A bit tighter can't hurt but there is no reason to go super fast. Most of the slugs we are talking about there are effectively "large revolver bullets", but not fired from a revolver. However the S.D. of an LBY style revolver bullets is very accurate in magnum revolvers and if fired from rifles at the same speeds the same math comes into play. A twist of 1-18 is used in a 357 mag many times. And the larger the diameter of the projectile, the less twist it takes because as I said above, it's the function of diameter X Pi that describes the helix of the equator of any bullet through the air. So if you were to ass 40 -60 grains more I believe a twist of 1-38 will still do the job. If in doubt tighten it up to about 1-32 to 1-34. But be sure the strength of the lands of the bullet are sufficient. As stated above, the grooved of the bore becomes the lands of the bullet, so narrower barrel lands and wide barrel groves are going to give excellent purchase on the bullet.

Keep the shank of the bullet about .001" under land size so you can load it with a rod. If I were making the mold I'd recommend making the top land of the bullet (last to enter the muzzle) only about .002" over groove size so it cuts on entry, but a tap with a small mallet will engrave it and then it seats easily. Have it made only .020 Tall.
Cast from WW metal and air cooled a bullet will obdurate fine, even if harder then pure lead. Bullets, when made too soft, actually do not kill AS WELL as balls from muzzleloaders simply because the terminal path through the bodies of animals often veers off when the nose smears badly. But hard balls go straight.

As I said above, my 62 cal flintlock exits all the game I have ever shot with one exception. A buffalo, -----and that one was still almost an exit (under the skin on the off-side) and was still in a straight line. A bullet with an LBT style nose, case semi-hard, will do anything you'd ever ask of it.

For an excellent overview and probably the best info you'll ever find on the subject, read "The Sporting Rifle and it's Projectile by James Forsyth, written in the 1860s. He found out 150 years ago what I re-learned for myself 40 years ago. Balls actually do a better job for most hunting. The gun he recommended the most was actually the same type as I have shown in the pictures above. It fires a ball of 1 Oz (437 Grains) and from the muzzle to about 100 yards it shoots where it points. past 100 yards you need to hold the sight picture a bit higher, but out to about 150 it's a very easy rifle to make kills with. Once you go out past 150 is where bullets start to overtake balls, but the in the real world about 98% of all you kills with a muzzleloader are at 125 and less.


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DarylS
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Re: 20 bore rifle twist [Re: szihn]
      #361985 - 14/02/22 11:08 AM

Breech loader changes everything as to size. Groove diameter is just fine, in fact, perfect.
What action are you going to use?
I have no experience loading black powder in 20 bore hulls, so I have no idea what powder charges could or should be used.

--------------------
Daryl


"a gun without hammers is like a Spaniel without ears" King George V


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Longknife
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Re: 20 bore rifle twist [Re: DarylS]
      #362201 - 18/02/22 08:28 AM

Steve, If making a black powder breech loader do the specs stay the same?

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Longknife


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DarylS
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Re: 20 bore rifle twist [Re: Longknife]
      #362208 - 18/02/22 10:25 AM

I have shot undersized, in fact only .0005" larger than bore diameter pure lead bullets in a breechloader and achieved 2" - 5 shot groups at 200yards, MOA, with aperture sights.
This proved the undersized bullets obturated perfectly, BEFORE they left the case, as there was no leading, the bored wiped clean of the fouling of 5 shots, with a dry patch.
Thus, I assumed the bullets obturated before moving very far if at all, from the case.
For this to work, there must be room in the case/chamber for this to happen, I also assume.

--------------------
Daryl


"a gun without hammers is like a Spaniel without ears" King George V


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szihn
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Re: 20 bore rifle twist [Re: DarylS]
      #362372 - 20/02/22 09:17 AM

The design for the bullet is basically the same for both muzzleloader and breach loader if the rifling is the same, but the specs would be different. Daryl is correct in saying the shank (body) of the bullet's lands are going to be made to drop at groove diameter of the barrel for a breach loader. So in other words if the grooves of your barrel were .620" you wan the shank of the bullet to also be .620"

For a muzzleloader the front land is slightly "too big" so it has to engrave when loaded, which keeps it from sliding out if the muzzle is pointed down, but the shank of the bullet should be .001 under land diameter so you can easily load it. You don't want a press fit. Obturation shortens the bullet upon firing. which makes it "fatter" and fills the grooves. In effect the rear of the bullet starts to move forward and sideways before the front of the bullet can, and that's what known as obduration. All soft bullets do this to some extent, but with a breach loader there is far less because at groove diameter, the bullet has no room to upset as it starts.


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Longknife
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Re: 20 bore rifle twist [Re: szihn]
      #362547 - 23/02/22 02:33 AM

Steve, I have been calculating the specifics of this breech loading bullet barrel and here are the specs I came up with .... .

30 inch barrel
1 1/8 to 1 taper
4150 steel
.620 bore
1-38 twist
.004 deep rifling
.180 grooves
.060 lands
radius on the inside corners of the grooves
round the corners of the lands

I think I have covered it all, let me know if I need to change anything before sending specs to barrel maker, Thanks, I appreciate your help, Ed

--------------------
Longknife

Edited by Longknife (23/02/22 02:34 AM)


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DarylS
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Re: 20 bore rifle twist [Re: Longknife]
      #362571 - 23/02/22 05:57 AM

Looks good to me, Longknife. 4150 is a bit "overboard" for a lower pressure smokeless barrel, imho.

--------------------
Daryl


"a gun without hammers is like a Spaniel without ears" King George V


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