Want to build a derringer.

[gjohnsoniv]

I have recently designed I want to build a derringer chambered in .22 short. The only question I have is about the barrel. Would it be better to put a liner in or use an old rifle barrel, and what pressures am I looking at. I.E what steel would be the best to use for the barrel over the liner or for the barrel.

[DaveS]

What kind of little deringer are you trying to build? Would it not be cheaper, easier or even SAFER to purchase one? I've built quite a few Black Powder weapons before, but not sure how to answer your question without taking on the liability of telling you so, just in case you blow your freek'n fingers off!

[gjohnsoniv]

Finally someone responds. I want to chamber one for .22 short, so I don't think that the pressures would be too high.

[DaveS]

Why .22 short if you don't mind me asking? That's an aweful little bullet for something! I had a friend shot with one while in high school. It stuck in his arm and he "sqezzed his skin" and the bullet popped up to the surface and he removed while waiting on and ambalance and police. Are you wanting it for "self defense?"

Edited May 16, 2012 by wd-40

[Sheepdog]

Would it really matter if it were a smoothbore? It's a derringer. It's a .22 short. Seems that the best use for it would be to jam it into the target before pulling the trigger. Hmm...Bad Guy Bellies: the Silencers that require no ATF tax stamp...

[gjohnsoniv]

No, not for self defense by any means. Just something to build so I can say I've done it, and they just have caught my interest lately. Can't do smoothbore Sheepdog, it would fall under the short barreled shotgun ruling.

[peejman]

According to this... http://www.saami.org/specifications_and_information/publications/download/208.pdf the max pressure for a high velocity .22 short is 21,000 psi. That pressure is then used to calculate the stress in the barrel material, which is then used to pick a material that gives adequate properties.

My assumption is that the chamber would be modeled as a thick walled pressure vessel to calculate the stress. That's not entirely accurate, but should give a conservative estimate. If you know the dimensions of the chamber (both inside and out) the stress calculation isn't particularly difficult. The link above also gives standard chamber internal dimensions. The outside dimensions can be varied to change the stresses and tailor to a particular material.

Here's a calculator for the stress. I have not verified it's accuracy. http://www.engineeringtoolbox.com/stress-thick-walled-tube-d_949.html

If you don't want to go through all that... just get a .22 LR barrel and cut it to your desired length.

[gjohnsoniv]

I don't mind doing the calculations, and I was considering going the barrel route.

[gjohnsoniv]

I like that engineering site, good info. I'm going back this fall to finish my engineering degree so that kinda thing floats my boat.

[peejman]

I like that engineering site, good info. I'm going back this fall to finish my engineering degree so that kinda thing floats my boat.

Good luck with school. I probably do more real engineering work with stuff like this than at my day job, but such is life.

There are several good engineering related web sites and apps, if you have a fancy phone. The online calculators and such are neat, but without understanding the underlying theory it's really easy to make mistakes and not know it.

[gjohnsoniv]

Good luck with school. I probably do more real engineering work with stuff like this than at my day job, but such is life.

There are several good engineering related web sites and apps, if you have a fancy phone. The online calculators and such are neat, but without understanding the underlying theory it's really easy to make mistakes and not know it.

Thank you. Is your day job being an engineer? I'll have to look into that for my droid. Right, I know they aren't a substitution for anything but it's nice having that information out there if you need it.

[peejman]

Thank you. Is your day job being an engineer? I'll have to look into that for my droid. Right, I know they aren't a substitution for anything but it's nice having that information out there if you need it.

Yep, been one (ME) for 13 years and counting. Had 3 different jobs in 3 different industries. Happy to talk about it more if you like.

http://www.asme.org/kb/news---articles/articles/technology-and-society/mobile-apps-for-engineers--what%E2%80%99s-in-store-

http://www.asme.org/kb/news---articles/articles/technology-and-society/10-ipad-apps-for-engineers

[gjohnsoniv]

That's actually exactly what I want to do.

Thanks for those links, I will have to look into a couple of those if they have them for the Android platform.

I would definitely like to talk to you since you're pretty close by.

Edited May 17, 2012 by gjohnsoniv

[peejman]

Off topic....

Here's a condensed version of the speech I've started giving students I talk to...

First, forget the possibility of getting an engineering degree in 4 years. Plan for at least 5. Assuming you're a traditional student, you have nothing but time. You probably don't think so, but trust me. Get a wife, couple kids, mortgage, 50+ hr/wk job, ... options get limited real fast. If money is tight, strongly consider entering a community college transfer program. It will take a little longer to finish, but you'll save a lot of money. It's a great way to get through all those useless classes some nitwit administrator thinks you need to be "well rounded". It'll give you more time to concentrate on the important stuff at the university.

Take every class you think might be interesting, regardless of topic. Again, you have nothing but time and they're free. If you're a hunter, take a few wildlife classes. If you like music, take a few music classes. History buff? Take a history class, etc. You never know where they'll take you. At the very least, you can audit the class. No grade to worry about, just a few hours per week. The mind needs distraction from all the engineering stuff that's being crammed in. I regret not taking advantage of several opportunities when I was in school.

It's critical that you fully understand the fundamentals you learn in the first couple years. Work very hard to maintain a good GPA. As you gain class hours, the effect of an individual class grade is reduced. Start with a good GPA (3.0 or higher) and you'll likely keep it. Start poorly and it's really tough to dig out of that hole. A 4.0 isn't necessary, some employers even frown on that. They think you're a book nerd with no practical/people skills. That said, don't forget to have fun... party with friends.... blow off some steam, engineering school is tough. College is way more fun than working for a living.

In a bigger school, it's easy to become a number and just slide through. The classes are large and there's little individual student/faculty interaction. If you have questions or aren't sure, ask. Both in class and outside of class. Some professors won't give you the time of day, but some will be very helpful. Having professors know your name and face can have benefits. For that matter, get to know the department secretaries too. You'll be surprised how much help they can be.

Internship/co-op experience is an absolute must these days. Don't wait until you're a senior for the internship, do it as early as you can. Your primary goal for the internship is to decide if you really like engineering (and make a little cash). You don't want to be 2 semesters from graduating and decide this sucks. If you get a full-time internship, take night classes while you're working. You'll be surprised at how fast you get away from being studious.

The job market is tough these days. New graduates are competing with guys like me. You need something that makes you stand out. Get involved in extra-curricular student activates/societies/projects.... hands-on stuff where you're actually building something, stuff that involves groups. You'll gain very valuable organizational and people skills.

If you have any thought on continuing on to grad school, do it now. Here's where having the faculty know you helps considerably. Let them know you're interested. Assistantships can be available that make grad school basically free. Talk to other grad students to see what it's like. Choose carefully, some professors like getting their grad students through quickly, some keep them around a long time. Some might say it's better to wait and let your employer put you through school. Wrong. Few employers do that anymore. Of the rare places that do, most require you to pay for everything up front and they'll reimburse you later.

There's plenty more, but that's enough for now...

[gjohnsoniv]

Haha you can save the rest for if we meet. As it stands right now I have all non-engineering pre-requisites done so I think I'm good on history, language, arts, and all that other fun stuff.

[Jonnin]

I have no experience here, but my advice is to do the same thing anyone would do when making anything for the first time with no clue how to proceed. Asking is a great first step --- so that is out of the way now. If I were going to do this, I would try some of these ideas.

1) google it, to see if someone else has done it already. At the least, you might get to see a video of some idiot blowing themself up and learn some important safety tips.

2) check out the free gun manuals pages online. A lot of older guns have everything shy of a 3-d cad drawing of the design. Modern folks are more protective of their designs, but you might find a parts list and total blown up diagram of exactly what you want to make.

3) expensive, maybe, but hit a gunshow and buy an example to tear up. This gets you 2 things: you can probably steal the barrel, and you can take it apart to see how things are made and why each part is where it is. You can learn a LOT from taking things apart if you go slowly and try to understand what you have. Put together, take it apart, a few times.

4) From here, design your own. Consider stealing the barrel, and possibly other parts as you see fit. If you plan to exactly copy this design, you could even make one part at a time and replace them in the original until it is a new gun.

5) don't forget to figure out whatever you must do legally for making a handgun (this may be an issue!).

6) When you fire it, consider doing so with a string from a goodly ways back. Even a lowly 22 short has plenty of danger in that little case.

Good luck with it. You probably knew all this, but hey, sometimes its hard to get started on something and a list helps...

[gjohnsoniv]

I have no experience here, but my advice is to do the same thing anyone would do when making anything for the first time with no clue how to proceed. Asking is a great first step --- so that is out of the way now. If I were going to do this, I would try some of these ideas.

1) google it, to see if someone else has done it already. At the least, you might get to see a video of some idiot blowing themself up and learn some important safety tips.

2) check out the free gun manuals pages online. A lot of older guns have everything shy of a 3-d cad drawing of the design. Modern folks are more protective of their designs, but you might find a parts list and total blown up diagram of exactly what you want to make.

3) expensive, maybe, but hit a gunshow and buy an example to tear up. This gets you 2 things: you can probably steal the barrel, and you can take it apart to see how things are made and why each part is where it is. You can learn a LOT from taking things apart if you go slowly and try to understand what you have. Put together, take it apart, a few times.

4) From here, design your own. Consider stealing the barrel, and possibly other parts as you see fit. If you plan to exactly copy this design, you could even make one part at a time and replace them in the original until it is a new gun.

5) don't forget to figure out whatever you must do legally for making a handgun (this may be an issue!).

6) When you fire it, consider doing so with a string from a goodly ways back. Even a lowly 22 short has plenty of danger in that little case.

Good luck with it. You probably knew all this, but hey, sometimes its hard to get started on something and a list helps...

I found a diagram for one called the "Child's Derringer Pistol" (Named after the designer) and I'm basing it off that design. The gun show route I am considering for a donor gun or at least a 10/22 barrel or something to cut up and mill. I have checked on all the regs to make sure I'm legal. As for the string idea, I was going to do that anyway because I have no room to lose a finger or injure one. Edited May 17, 2012 by gjohnsoniv