Barrel blank

[Scota4570]

OK, a 7/8"-14 plug. 0.165 walls, 0.720" bore = 1.05" OD. Is your OD 1"?. That leave 1/16" (.0625") of steel intact around your plug threads. I believe that is unsafe regardless of the strength of the main tube.

 

[BrownBear]

Though I haven't seen a muzzleloader barrel come apart at the breech firsthand, I've seen the aftermath. Bud had it happen, and for years now he's been learning how to get his jobs done without his right thumb to help.

Thinkaboudit.... No do-overs if you're wrong about enuffsteel and lots you might have to contend with afterward.

I'm not a liberal like some here. I'm downright conservative.

 

[M. De Land]

If it’s 4140, I wouldn’t worry about it. Plenty of margin for error. As for threads, that’s nearly 3/16” wall thickness . I recall the TC oddball breechplug threads of 11/16x20. They used that on everything including 13/16 barrels. Which left 1/16” a side. Properly fitted, you shouldn’t have any gas pressure in the threads anyway. GM used 1137 steel that wasn’t nearly as strong as 4140. Also recall Gen Julian Hatcher trying to blow up a Springfield 30/06 barrel (aisi4140). He kept turning the chamber area down and shooting it. Finally had it down to 1/16” over the chamber. Still it wouldn’t let go with std 55,000psi loads. He had to put high pressure proof loads into it and IIRC, had it over70K before it finally went. You’d be lucky to get 10k in that barrel.

1137 is gun barrel quality steel having very good numbers in tensile,elongation and shock load similar to carbon manganese ordnance steel which was used for most of our service arms in WWll. The leaded steel used by many muzzle loading barrel makers has very poor shock load numbers and while it machines beautifully is not certified gun barrel steel. The low pressure of black powder in muzzle loading arms allows it's use but the added strength of 1137 makes for a safer barrel steel and is the reason I always choose Green Mtn barrels if possible.
The shock load numbers of lead steel is low even when hot rolled but is really dismal in cold rolled steel. As the ambient temperature goes below zero weapons made of this material and used in this environment I feel are questionable from a safety standpoint especially with heavy charges often used for hunting purpose.

 

[brayhaven]

K

A word of warning, if I may.

Proofing a barrel can damage the barrel in ways that aren't easily detected.
Internal cracks can be created and to detect these the barrel must pass a non-destructive test such as a Magnetic Particle Inspection. Not quite as good as a MPI is a Fluorescent penetrant inspection. It only tests for surface flaws but that is still much better than not doing any testing at all.

The mag-partical inspection can be done by companies which specialize in rebuilding engines. They use it to test the crankshaft for cracks and other flaws.

Before using a barrel that has been proofed I urge the shooter to have a NDT preformed. If that is not possible, IMO if the barrel is newly made from quality material (no welded "seamless tubing), it is better not to run a full load proof test.

If the barrel is very old, the Non-Destructive testing is almost mandatory if one wants to shoot the gun.

Wonder why they don’t do this in the proof houses all over the world? Generally any damage that is caused would show up in the dimensional measurements. Might not in a hardened steel, but in a “soft”
barrel I wouldn’t worry, and have never seen a problem all the years I’ve been doing it. There’s a huge safety margin. The proof test is more to reveal hidden flaws in the steel. US made guns aren’t even proofed and failure is about non-existent using SAAMI loads. The old “magnafluxing” isn’t foolproof either. I’d much prefer a proof load and measurement. Then I’m comfortable shooting lighter loads. It’s worked since the 1800s If you know of a (non error), failure, I’d appreciate the details.

 

[brayhaven]

OK, a 7/8"-14 plug. 0.165 walls, 0.720" bore = 1.05" OD. Is your OD 1"?. That leave 1/16" (.0625") of steel intact around your plug threads. I believe that is unsafe regardless of the strength of the main tube.

Shouldn’t be a problem if the plug is properly seated against the shoulder. T/C did it for many years using their 11/16x20 breech plug thread in 13/16 barrels. 3/4” barrels are routinely threaded for 5/8x18 plugs.

 

[brayhaven]

1137 is gun barrel quality steel having very good numbers in tensile,elongation and shock load similar to carbon manganese ordnance steel which was used for most of our service arms in WWll. The leaded steel used by many muzzle loading barrel makers has very poor shock load numbers and while it machines beautifully is not certified gun barrel steel. The low pressure of black powder in muzzle loading arms allows it's use but the added strength of 1137 makes for a safer barrel steel and is the reason I always choose Green Mtn barrels if possible.
The shock load numbers of lead steel is low even when hot rolled but is really dismal in cold rolled steel. As the ambient temperature goes below zero weapons made of this material and used in this environment I feel are questionable from a safety standpoint especially with heavy charges often used for hunting purpose.

Never knew anyone made smokeless cartridge rifle barrels from 1137. I wouldn’t want to shoot one . I agree on the quality of GM 1137 ml barrels, but they make all their cartridge barrels including BP cartridge barrels out of 4140. I recall Hoppy at H&H barrels made his ML barrels from 4140 chromoly which was way overkill. But he felt it also helped with wear resistance from ram rods etc. I still have a couple of his barrels. I think Getz used 12L14 for awhile. Not sure what the other makers use. But I’m sure it’s sufficient, or they wouldn’t use it given today’s litigious atmosphere.

 

[Scota4570]

Shouldn’t be a problem if the plug is properly seated against the shoulder. T/C did it for many years using their 11/16x20 breech plug thread in 13/16 barrels. 3/4” barrels are routinely threaded for 5/8x18 plugs.

Disagree....The TC plugs in a 45 caliber barrel are a different matter. The 45 caliber barrel has an area of 1.41". The 72 caliber barrel has an area of 2.26". The force on the 1/16" of steel is 1.6 times more on the 72 caliber. To make the TC force per area of steel the same in the 72 caliber, as 45 caliber, it would need to be 0.038" thick. That is not safe. If we go the other way and scale it up to 72 caliber, your TC example would be 0.10" thick per side. That makes the OD of the barrel 1.075" , to make it equal to the TC.

I see Track sells no 12 ga fowler barrels less than 1 1/8 at the breech end. I think this is a pretty sensible minimum figure. This is not worth dyeing for...really, please be safe.

 

[Scota4570]

I've been thinking about this thread.

I think the best answer is to consult a muzzle loading barrel maker. Someone who makes 12 ga barrels for fowlers for instance. Ask nicely for a moment of his time, and if he agrees to answer a technical question, ask it.

None of us are barrel makers. We have speculated on relevant and irrelevant issues for two pages. You need advice from somebody who really knows.

Good luck.

 

[brayhaven]

Shouldn’t be a problem if the plug is properly seated against the shoulder. T/C did it for many years using their 11/16x20 breech plug thread in 13/16 barrels. 3/4” barrels are routinely threaded for 5/8x18 plugs.

Disagree....The TC plugs in a 45 caliber barrel are a different matter. The 45 caliber barrel has an area of 1.41". The 72 caliber barrel has an area of 2.26". The force on the 1/16" of steel is 1.6 times more on the 72 caliber. To make the TC force per area of steel the same in the 72 caliber, as 45 caliber, it would need to be 0.038" thick. That is not safe. If we go the other way and scale it up to 72 caliber, your TC example would be 0.10" thick per side. That makes the OD of the barrel 1.075" , to make it equal to the TC.

I see Track sells no 12 ga fowler barrels less than 1 1/8 at the breech end. I think this is a pretty sensible minimum figure. This is not worth dyeing for...really, please be safe.

I’m trying to figure out what you’re worried about. Thought it was the 1/16 of steel around the breech plug threads? There’s a difference between breech pressure and chamber pressure. Look at locking systems on shotguns, vs rifles. If you’re worried about stripping the plug threads due to force applied to the breech plug face, that should be no issue with properly cut threads and enough depth. The depth is important. The important part is to seat the plug against the shoulder so there’s no pressure getting into the threads. That’s what caused the problems with the savage smokeless muzzle loader. Also pressures in a 12 ga. shotgun will be less than in a smaller bore rifle. We’re also talking about a much stronger steel than anything normally used for ml barrels.
I’ve made some ml barrels, in 4140, and 416, have proofed a lot more ml & cartridge. and examined probably thousands. If the barrel he’s talking about passes proof, it should be plenty safe. And I’d take a 4140 steel barrel with 1/16” less wall thickness any day to a weaker steel normally used in ml barrels.
this barrel would probably have a safety factor of 6-8 times the pressures he’d generate with the load he mentioned.
I’m just going by 40+ years gunsmithing..writing, researching etc. your advice to ask a barrel maker wouldn’t hurt. Though I’d bet the barrel maker would try to sell him a barrel .

 

[brayhaven]

This thread got me thinking and recalling some of the incredibly thin barrels I’ve seen on shotguns that had been used for generations. Some were so thin, I removed dents with wood dowels.
Don’t really recall keeping any notes on the wall thicknesses I encountered though. So I looked around the shop for some commercially made guns/barrels. I make all my guns and the only commercially made 12 gauge I have is a Navy Arms “magnum” model double.
I measured that one at the breech and it measures 1.020”. Smaller than the barrel blank in this thread. Since any 12 ga would require at least .850” or so breech plug to get a decent shoulder, I assume this one has that or more. Bought this gun new for some clay bird shooting and it was advertised as the “magnum” model that could handle all 10 and 12 ga loads as well as light 8 ga loads. No idea what it can handle, but I’ve shot some very strong and uncomfortable 1 3/4 oz turkey loads in it with plastic wads and copper plated shot. No idea what steel they used, but I drilled and tapped it for thin wall choke tubes and it machined easily. Seemed to cut more easily than cartridge shot barrels. It has Italian proofs and apparently was made by pietta.

 

[russellshaffer]

Merry Christmas and a happy new year to all. You folks have certainly given me a lot to chew on. My barrel measures 1.060 on the OD, just slightly more than the Navy Arms "magnum". I have no intention of hunting with this thing - matchlocks are illegal for hunting in Oregon, probably due the usual dry conditions in the fall and the danger of fire. I won't even shoot a caplock anywhere that has vegetation. So as of right now, I plan to do a mild proof firing and then hold my loads to something in the 50 to 60 grain range. I think Zonie has a very good point about proofing - almost blowing something up and then to keep chipping at it with lighter charges doesn't really seem like a good idea. I don't like heavy recoil anyhow so why abuse my shoulder to no purpose. Just for grins, I am attaching a photo of an Indian revolving matchlock. I really wonder about the steel (?) in the cylinder but it hasn't blown up. A scary looking thing to my thinking and nothing I would fire. Any more comments and suggestions are very welcome and I read and think about all of them.

 

[Scota4570]

Brayhaven said, "I’m trying to figure out what you’re worried about."

The breech end might separate from the rest of the barrel when you fire it. The area around the threads at the nose of the plug is wafer thin. If you make a relief cut to get full depth threads it will be thinner. It may give way first shot or it may work harden over time and let go without warning in the future. If you ever short seat a ball the danger will be 10X worse.

 

[brayhaven]

Brayhaven said, "I’m trying to figure out what you’re worried about."

The breech end might separate from the rest of the barrel when you fire it. The area around the threads at the nose of the plug is wafer thin. If you make a relief cut to get full depth threads it will be thinner. It may give way first shot or it may work harden over time and let go without warning in the future. If you ever short seat a ball the danger will be 10X worse.

Never been a problem with many production guns, with even less metal in that area. And with MUCH weaker steels. Why would that area “work harden”? Short seating a ball always poses a risk in ANY ML gun. But a barrel made of 4140 would be much less likely to fail than 1137 or other weaker steels. This barrel, properly breeched, will be well within accepted gunmaking standards for operating pressures. For custom as well as production guns. If anything, it’s overkill.
Muleskinner.

 

[garryd]

4140 Steel is a heat-treatable steel and the ultimate strength, yield strength, ductility, hardness, and impact toughness are all dependent upon the heat treatment and can vary greatly based upon that heat treatment. The specifications for 4140 steel, like those for other steels, specify minimum and/or maximum compositions and properties. The specification for yield strength is minimum (allowable) yield strength and actual yield strength may, and probably does, exceed the specified minimum. Steel manufacturers can provide Mill Test Reports for every batch of steel that they make and you can be assured that major gun manufacturers have those records on file for every firearm that they manufacture. While higher yield strength can be attained by selected heat-treatment, so doing can negatively influence impact toughness, ductility and machinability.

When one is purchasing a barrel from a reputable manufacturer, one can only assume that the base steel and the heat treating to which it has been subjected are suitable for purpose.

Yes, firearms do demonstrate good engineering practice and demonstrable compliance with the physics that define the stresses in firearms, even .44 Mag cylinders.

The axial stress in a gun barrel is the least significant stress in the barrel. (The calculation provided previously incorrectly calculated the cross sectional area of the example barrel; 0.600” diameter does not yield an area of 0.3421 square inches). Designing a gun barrel based only upon axial stress would be an invitation to disaster. Even in a thin walled barrel, this axial stress would only be half of the most significant stress, circumferential stress. Barrels fail by bursting and not by tearing off and projecting pieces of barrel downrange.

The gun barrel will be subjected to radial stress which, at the bore will be equal to the internal pressure and will diminish to zero at the exterior of the barrel. The barrel will also be subjected to circumferential (hoop) stress which will be highest at the bore and lowest at the exterior of the barrel. Circumferential (hoop) stress will be the most significant stress in the barrel. The process of autofrettage can move the area of highest circumferential stress away from the bore and was, I believe, first developed to create stronger cannon barrels. Autofrettage can be employed by cold expanding the inside of a gun barrel n order to put the near-bore metal into initial compressive stress.

In a muzzle loader with a threaded breech plug, other significant stresses will the the shear stresses on the exterior threads of the breech plug and the shear stresses in the internal threads of the barrel and upon the axial stress of the reduced barrel in the threaded portion. As noted by others, in a breech plug which seals the rear of the barrel on its face, there would be no internal pressure in the threaded portion to contribute to circumferential or radial stresses.

Before any meaningful stress analysis can be completed, the internal pressure which has to be dealt with must be determined. Unlike modern firearms wherein ANSI/SAAMI standards provide criteria to which maximum pressures must conform for ammunition and to which firearms must be designed, there are no such standards for muzzle loaders. The burning rate for powder is dependent upon surface area and so finer powders burn faster and produce higher pressures than more coarse powders. There is minimal information available on the pressures that may be generated by various combinations of calibre, amount of powder, coarseness of powder, weight of projectile, and/or barrel length. Internal ballistic calculations can provide good approximations of the average pressure required to deliver a projectile of given weight and diameter at a given muzzle velocity but peak pressure, which will occur at the breech end of the barrel will be predictably a number of times higher. A major advancement in the construction of cannons was the realization that the highest pressure occurs at the breech end and that barrels could be designed to lessen the metal thickness towards the muzzle by wall thickness following the pressure curve.

Then there is the potential for accidentally throwing a double charge of powder during a moment of distraction (have seen it done) or failure to seat the projectile thereby changing the density of loading or even forgetting to remove the ramrod from the barrel. And is short seating a ball actually 10X worse or maybe only 9X or maybe 11X or...?

 

[brayhaven]

4140 Steel is a heat-treatable steel and the ultimate strength, yield strength, ductility, hardness, and impact toughness are all dependent upon the heat treatment and can vary greatly based upon that heat treatment. The specifications for 4140 steel, like those for other steels, specify minimum and/or maximum compositions and properties. The specification for yield strength is minimum (allowable) yield strength and actual yield strength may, and probably does, exceed the specified minimum. Steel manufacturers can provide Mill Test Reports for every batch of steel that they make and you can be assured that major gun manufacturers have those records on file for every firearm that they manufacture. While higher yield strength can be attained by selected heat-treatment, so doing can negatively influence impact toughness, ductility and machinability.

When one is purchasing a barrel from a reputable manufacturer, one can only assume that the base steel and the heat treating to which it has been subjected are suitable for purpose.

Yes, firearms do demonstrate good engineering practice and demonstrable compliance with the physics that define the stresses in firearms, even .44 Mag cylinders.

The axial stress in a gun barrel is the least significant stress in the barrel. (The calculation provided previously incorrectly calculated the cross sectional area of the example barrel; 0.600” diameter does not yield an area of 0.3421 square inches). Designing a gun barrel based only upon axial stress would be an invitation to disaster. Even in a thin walled barrel, this axial stress would only be half of the most significant stress, circumferential stress. Barrels fail by bursting and not by tearing off and projecting pieces of barrel downrange.

The gun barrel will be subjected to radial stress which, at the bore will be equal to the internal pressure and will diminish to zero at the exterior of the barrel. The barrel will also be subjected to circumferential (hoop) stress which will be highest at the bore and lowest at the exterior of the barrel. Circumferential (hoop) stress will be the most significant stress in the barrel. The process of autofrettage can move the area of highest circumferential stress away from the bore and was, I believe, first developed to create stronger cannon barrels. Autofrettage can be employed by cold expanding the inside of a gun barrel n order to put the near-bore metal into initial compressive stress.

In a muzzle loader with a threaded breech plug, other significant stresses will the the shear stresses on the exterior threads of the breech plug and the shear stresses in the internal threads of the barrel and upon the axial stress of the reduced barrel in the threaded portion. As noted by others, in a breech plug which seals the rear of the barrel on its face, there would be no internal pressure in the threaded portion to contribute to circumferential or radial stresses.

Before any meaningful stress analysis can be completed, the internal pressure which has to be dealt with must be determined. Unlike modern firearms wherein ANSI/SAAMI standards provide criteria to which maximum pressures must conform for ammunition and to which firearms must be designed, there are no such standards for muzzle loaders. The burning rate for powder is dependent upon surface area and so finer powders burn faster and produce higher pressures than more coarse powders. There is minimal information available on the pressures that may be generated by various combinations of calibre, amount of powder, coarseness of powder, weight of projectile, and/or barrel length. Internal ballistic calculations can provide good approximations of the average pressure required to deliver a projectile of given weight and diameter at a given muzzle velocity but peak pressure, which will occur at the breech end of the barrel will be predictably a number of times higher. A major advancement in the construction of cannons was the realization that the highest pressure occurs at the breech end and that barrels could be designed to lessen the metal thickness towards the muzzle by wall thickness following the pressure curve.

Then there is the potential for accidentally throwing a double charge of powder during a moment of distraction (have seen it done) or failure to seat the projectile thereby changing the density of loading or even forgetting to remove the ramrod from the barrel. And is short seating a ball actually 10X worse or maybe only 9X or maybe 11X or...?

Interesting thread. I spent a lot of time at the H&H barrel works when I had a shop in Sarasota, it was only a couple hour drive. Picking up barrels and hanging out. They made modern cartridge barrels (button rifled) as well as ML barrels, using 4140 steels for all of them. He liked the toughness & wear resistance even though it was overkill for ML's. Said the ramrods and loading & cleaning was harder on them than shooting. He ordered his 4140 in 1 1/4" round bar stock annealed. The only heat treating he did was stress relief. To relax the barrel from the stresses induced by machining etc. Said that the needed strength came from the alloy and not heat treatment. Elasticity is a necessary trait in a gun barrel as well. As an outdoor writer and gun maker I talked with quite a few barrel makers, but never got into heat treatment beyond stress relief, so no idea what others did. I did barrel a lot of rifles with Shilen, Douglas, and other barrels and they all seemed to machine, chamber, thread, crown, drill & tap etc, about the same. Hoppy did some experimental work for the military as I recall, as well.
Green Mountain advertised their barrels as being annealed:
"Green Mountain muzzle loading barrels are made from 1137 steel, which is annealed and stress relieved."
A pretty good treatise on barrel steel and barrel making is here: http://www.steelhelixrifle.com/index_files/Page351.htm
He also stresses the importance of proofing a barrel, as has been the practice of most gun making countries around the world as well as the US military ordinance folks.
The barrel in this thread would likely never see pressures above 9K psi. A smaller caliber rifle barrel would encounter much higher pressures.
I've always followed successful design where possible and still proof tested. If we engineered our guns to account for software malfunctions (between the ears) like short seating etc. they'd all weigh 20 pounds and we'd need a gun bearer to follow us around the woods. .
Muleskinner