Internal Ballistics and Gun Barrel Design Application

[Broken Coconut]

Hello

I'm a mechanical engineering student and I've been studying the internal ballistics of guns for the last 3 years, it was first just a hobby since I've always loved those big cannons from sci-fi movies and then I suddenly wanted to design my own big cannons. I'm currently making my thesis about the design of an artillery gun barrel and I found this forum when I was finding information about guns and gun design, I think this is an amazing community with a lot of useful information.

These are some drawings I made to explain my project to my professors:

Some months ago I designed a 4cm/61 gun barrel using the internal ballistics theories I've been studying with the design knowledge I have from my career and made a 3D model of it. It was just a testing design to see if everything was going well with theories I've been studying.

4cm/61 Gun

The last year I had the idea of developing an application using the knowledge of my thesis, which means that such app would give you the data needed to understand the internal ballistics of guns and of course, it should design the gun barrel too. I've been developing such application since April since I have free time because of the lockdown.

COCOBALISTICA

This one would be the first version of the application in English (version 1.0), I had already made a beta version for testing purposes but it was in Spanish only. The application lets you see some parameters like velocity of the projectile inside the gun, internal pressure, projectile twist velocity inside the gun, burning rate, etc... You can plot such parameters to see how they behave with more details too. Since my first language is Spanish, I made the application in Spanish and English, it also does have the US and International (metric) systems of measurement and it is possible to make conversions of units in case you want the results in the international system of measurement but you have the data in the US system of measurement.

COCOBALISTICA 1.0 Screenshots:

Youtube video using the application:

For now the application only gives you the internal ballistics data but I will keep developing it until it designs gun barrels, something I hope to achieve soon but first I will release another version adding some details and fixing possible errors of the version 1.0. I think it would be useful for the people who tends to visit this forum because I noticed you can cast your bullets and make your own powder, saving you lots of money but, what if you could design your own gun barrel for any caliber, powder and steel alloy? I want the application to give you enough information to design your own gun barrel for any projectile, caliber and powder using the alloy you want (not all alloys are strong enough to be used but this is something that the app will tell you)... You could save money from buying new barrels when the one you are using for your gun is already worn by making it by yourself if you have the machining tools needed for it and you would know the approximate barrel life.

[303Guy]

That looks very interesting. Does your app go into chamber and throat design details?

[samari46]

As you are probably aware that some demilled 40mm, 3"x50 barrels and possibly some 5x54" barrels have been used in the past to build larger caliber muzzle loading and some breech loading barrels using U.S. Demilled barrels.Not making any promises as time has a way of disrupting things when people start making plans. My barrel is a cut down 40mm antiaircraft barrel. And since my lathe will only allow a 40" length of barrel between centers on my lathe. And due to the alloys used back then you cannot weld on the tube eothout extensive heating the tube prior to commencement of the welding and proper heating and cooling after the welds have been completed. reason for this is if the proper procedures are not done the welds will crack. So just about anything that attaches to the barrel must of course be threaded on. Breech plug, ring for the trunions plus any sighting equipment all have to threaded including a liner for the touch hole. That has to be made so it can be removed at a later time. As it wears out over time. Suggested material would be copper or some grade of stainless steel. There was a rather long thread done on the Gunboards forum some years back about building a cannon on a discarded section of cannon barrel. Most cannon builders usually work from established plans and try to get as close to the original plans as possible. You're mostly limited in doing so by the size of the tube and the size of the lathe your working with. Then proof testing comes into play. One video I watched years back the builder proofed his cannon with a full pound of powder. The carriage was basically destroyed but the tube passed the proof test with both black powder and ball. Youtube usually has some older videos done by Cannonman. Those are extremely well thought out and should help you out. There is also a chart that describes the proper powder charge in grains of black powder but you may also see a powder charge in ounces. Smaller cannon barrels like my 40mm may only consume a couple ounces of black powder. Some cannons are setup to fire the main charge of powder by fuse,others use friction primers which for some is probably the best way to fire a cannon. Frank

[Broken Coconut]

That looks very interesting. Does your app go into chamber and throat design details?

I have not included design yet, but yes I want it to have chamber details since it is part of the barrel too but I include the throat as part of the chamber and I'm not used to small firearms chambers, I hope they are not too different from artillery gun chambers. What I have in mind is that you give the dimensions of the chamber and/or dimensions of the cartridge case to the app, just in case someone wants to test a caseless ammunition or a separate loading bag (artillery).

These are the dimensions (mm) of the 4cm/61 Gun I designed:

[Broken Coconut]

As you are probably aware that some demilled 40mm, 3"x50 barrels and possibly some 5x54" barrels have been used in the past to build larger caliber muzzle loading and some breech loading barrels using U.S. Demilled barrels.Not making any promises as time has a way of disrupting things when people start making plans. My barrel is a cut down 40mm antiaircraft barrel. And since my lathe will only allow a 40" length of barrel between centers on my lathe. And due to the alloys used back then you cannot weld on the tube eothout extensive heating the tube prior to commencement of the welding and proper heating and cooling after the welds have been completed. reason for this is if the proper procedures are not done the welds will crack. So just about anything that attaches to the barrel must of course be threaded on. Breech plug, ring for the trunions plus any sighting equipment all have to threaded including a liner for the touch hole. That has to be made so it can be removed at a later time. As it wears out over time. Suggested material would be copper or some grade of stainless steel. There was a rather long thread done on the Gunboards forum some years back about building a cannon on a discarded section of cannon barrel. Most cannon builders usually work from established plans and try to get as close to the original plans as possible. You're mostly limited in doing so by the size of the tube and the size of the lathe your working with. Then proof testing comes into play. One video I watched years back the builder proofed his cannon with a full pound of powder. The carriage was basically destroyed but the tube passed the proof test with both black powder and ball. Youtube usually has some older videos done by Cannonman. Those are extremely well thought out and should help you out. There is also a chart that describes the proper powder charge in grains of black powder but you may also see a powder charge in ounces. Smaller cannon barrels like my 40mm may only consume a couple ounces of black powder. Some cannons are setup to fire the main charge of powder by fuse,others use friction primers which for some is probably the best way to fire a cannon. Frank

Thanks for your advice, I didn't think about welding cut down tubes, I've seen threaded muzzle brakes but this is the first time I read about using threads to merge tubes, it sounds great but I can not include something like that in the app for now. The app is going to work with stress theories I have studied in my career and monoblock barrels are the ones who fit the best with those equations, a merged barrel with threads would have a different stress behaviour that I would have to study in order to know how to make it safe. I have studied welding stress theories too and I think I can design a barrel merged with welding but it is not something I'm gonna include, at least not soon.

Since I base the design in stress theories, I'm limited by the information I already have, for example I have no experience designing a breech block and I have no scientific information or theories to design them yet, that's why I'm gonna limit the design to the gun barrel/tube.

The 40mm gun design I made was just for design testing purposes, I had information about two different 40mm guns and I made my first design as a 40mm gun too because I could compare its performance with the other guns that I have information about. I would never suggest you to use copper for the barrel/tube because it is a too weak material. You can know how strong a material is by finding its yielding and ultimate stresses, at least in this case that's what I use.

For Copper:
Attachment 268473

The app is going to design the barrel based on internal ballistics and stress theories, a trouble that people who make their own black powder may experience is that they can not measure exact internal ballistic values because the shape of the propellant grain is too important for its burning behaviour and home-made black powder doesn't have an uniform shape. By the way I think it is possible to fix this for small firearms at least, if you can measure the maximum internal pressure for your black powder charge, it is possible to design a safe barrel/tube as long as you use such charge as a maximum permissible charge.

In order to make the design safer I'm gonna include the security factor, if this is the first time you read about it, don't worry, it is something easy, example:

If you want to design a chair for a maximum weight of 150 lbs, you need to make it safe to use for people who weights exactly 150lbs.

SF= Security Factor
MPW= maximum people weight
CR= Chair Resistance

You use this simple formula:

CR/SF=MPW

Then, if you want a security factor of 2 (it can not be less than 1), you your chair theoretical resistance must be:

CR= SF * MPW = 2 * 150lbs
CR=300 lbs

Why is it important? That's because sometimes design theories aren't 100% accurate even when they are based on physics and math, or you want to take manufacturing errors into account and make it safe anyway. And even when your chair can be used by people who weighs 300lbs, it should not be used by people who weighs more than 150lbs.

When talking about firearms I've seen that "security factor" isn't mentioned but I see "security pressure", it is the same logic. Security factor is too important to design firearms because most ballistic theories aren't 100% accurate and I've not seen a 100% accurate ballistic theory, maybe they exist, I just don't have such information.

Of course, proof testing is always needed, but you need to be sure that what you are going to test is safe even before testing it, that's the purpose of using engineering to design things.

And again, thanks for your advice, there are many things that aren't mentioned by books and I've found a lost of useful information on this forum.