09-01-2017, 05:52 PM
About seven or eight years ago, both of my kids were home on summer break and I was trying to share some of my interests with my boy. He seemed oblivious to most of them but he has always enjoyed shooting. He liked popping clay pigeons that we threw with a hand trap on a nearby beach. He also liked shooting tin cans that we brought with us (removing when we left) with a little Ruger Single Six.
During a casual discussion, he recalled how I used to bring a Ruger Speed Six revolver on camping trips, loaded with a few shotshells and a couple of handloads. This was sort of our contingency "snake gun" and although we never pointed it at a single snake, we did kill a few vicious and aggressive tin cans.
It was a pain to carry that heavy thing around for an encounter with odds of thousands to one happening. It also didn't take much imagination to figure that (although holstered) the revolver was probably intimidating to those who might be encountered in the woods - maybe even anger in some hikers, bird watchers and so forth,
The boy wondered aloud about building a single action, single shot, hand-held shotgun (.410). Well, maybe if it was configured similar to an antique, it would appear “friendlier” I thought. Other than the legal issues, it seemed like a possibility of stimulating his interest in both mechanical design and metalworking (at the time, he was a first year student and hadn't declared a major yet).
So I used the opportunity to motivate/teach, sporadically working on the project over a year, explaining and sometimes demonstrating the steps of how products evolve from conception, through initial research and planning, preliminary analysis followed by design and finally to building a prototype.
The original thought was to build a smoothbore .410 hand-held shotgun but home-built firearms have legal restrictions in California as we found out after some internet research. The barrel must be rifled and there is a minimum length. (BTW, local law folks, when questioned about this, had no answers to my questions on the topic.)
A much simpler project would have been a black powder smoothbore kit which would be completely legal, for some weird reason, easy to assemble easy to cut down/modify and easily loaded with loose shot. But we had no interest in a muzzle loader and building a kit didn't present much of a challenge (nor would that process have illustrated the points that I hoped to make).
After researching and selecting materials, trying to understand and quantify the impulse load of the discharge and other typical problems that are encountered in the early stages of any design, we came up with a tentative model.
The basis would be a barrel rifled for a .45 Colt cartridge that can accommodate a .410 shotshell. Along the way, we performed a preliminary stress analysis using a free finite element analysis (FEA) program downloaded from the internet. (BTW, I envisioned the rifling to be a series of deep scratches, if you get my drift.)
Maybe this detailed exercise was too much for my son because he lost all motivation and selected journalism as his major, ha-ha-ha. So the project died from lack of interest. A shame because this post would surely have been WAY more interesting if some of the building steps and results of the finished shotgun could have been shown.
I was deleting old drawing files on the computer a while back and found our LibreCAD drawing of this project and I thought that it might be of interest. So here's the drawing (pistol includes a safety, by the way) and the preliminary stress analysis that we came up with:
(Click to obtain an enlarged view of either)
The stress model was simplified to consider only the receiver. I used a free FEA application from the internet at the time, which was limited in the part complexity that it could analyze. This was the primary reason for modeling the receiver exclusively but also, the receiver is presumed to be the most highly stressed portion of the pistol.
The red areas are the most highly loaded and the stress levels are shown in the left margin. The figures are too small to see, unfortunately. The shape depicted is the highly exaggerated deformation under the impulse load of firing.
The latching mechanism must be designed to accommodate this stress with double safety margin. If the project continued, I wouldn't have felt comfortable just estimating this stuff. As a conservative engineer, I’d base a design on something more tangible than intuition, LOL. Especially when it comes to something that I’ve never done before !
If I did this now, the evaluation would be different. I obtained a very powerful FEA application a few years ago, called “LISA”. Using LISA, a comprehensive model of the tin can gun could be developed and the stress on each part predicted. The latching device for the tipped barrel might change or be refined at the time as a result of a more comprehensive analysis.
It would be a time-consuming project but fun for a retired guy. It’s probably unnecessary to mention that a “proofing” process would be part of the project. I should note that I never expected performance exceeding moment-of-garbage-can at five feet.
I should also note that, if I could get the weight down, it would not be particularly pleasant to shoot
P.S. Incidentally, “LISA” used a few of my analyses as examples on their website although they are not related to this project.
During a casual discussion, he recalled how I used to bring a Ruger Speed Six revolver on camping trips, loaded with a few shotshells and a couple of handloads. This was sort of our contingency "snake gun" and although we never pointed it at a single snake, we did kill a few vicious and aggressive tin cans.
It was a pain to carry that heavy thing around for an encounter with odds of thousands to one happening. It also didn't take much imagination to figure that (although holstered) the revolver was probably intimidating to those who might be encountered in the woods - maybe even anger in some hikers, bird watchers and so forth,
The boy wondered aloud about building a single action, single shot, hand-held shotgun (.410). Well, maybe if it was configured similar to an antique, it would appear “friendlier” I thought. Other than the legal issues, it seemed like a possibility of stimulating his interest in both mechanical design and metalworking (at the time, he was a first year student and hadn't declared a major yet).
So I used the opportunity to motivate/teach, sporadically working on the project over a year, explaining and sometimes demonstrating the steps of how products evolve from conception, through initial research and planning, preliminary analysis followed by design and finally to building a prototype.
The original thought was to build a smoothbore .410 hand-held shotgun but home-built firearms have legal restrictions in California as we found out after some internet research. The barrel must be rifled and there is a minimum length. (BTW, local law folks, when questioned about this, had no answers to my questions on the topic.)
A much simpler project would have been a black powder smoothbore kit which would be completely legal, for some weird reason, easy to assemble easy to cut down/modify and easily loaded with loose shot. But we had no interest in a muzzle loader and building a kit didn't present much of a challenge (nor would that process have illustrated the points that I hoped to make).
After researching and selecting materials, trying to understand and quantify the impulse load of the discharge and other typical problems that are encountered in the early stages of any design, we came up with a tentative model.
The basis would be a barrel rifled for a .45 Colt cartridge that can accommodate a .410 shotshell. Along the way, we performed a preliminary stress analysis using a free finite element analysis (FEA) program downloaded from the internet. (BTW, I envisioned the rifling to be a series of deep scratches, if you get my drift.)
Maybe this detailed exercise was too much for my son because he lost all motivation and selected journalism as his major, ha-ha-ha. So the project died from lack of interest. A shame because this post would surely have been WAY more interesting if some of the building steps and results of the finished shotgun could have been shown.
I was deleting old drawing files on the computer a while back and found our LibreCAD drawing of this project and I thought that it might be of interest. So here's the drawing (pistol includes a safety, by the way) and the preliminary stress analysis that we came up with:
(Click to obtain an enlarged view of either)
The stress model was simplified to consider only the receiver. I used a free FEA application from the internet at the time, which was limited in the part complexity that it could analyze. This was the primary reason for modeling the receiver exclusively but also, the receiver is presumed to be the most highly stressed portion of the pistol.
The red areas are the most highly loaded and the stress levels are shown in the left margin. The figures are too small to see, unfortunately. The shape depicted is the highly exaggerated deformation under the impulse load of firing.
The latching mechanism must be designed to accommodate this stress with double safety margin. If the project continued, I wouldn't have felt comfortable just estimating this stuff. As a conservative engineer, I’d base a design on something more tangible than intuition, LOL. Especially when it comes to something that I’ve never done before !
If I did this now, the evaluation would be different. I obtained a very powerful FEA application a few years ago, called “LISA”. Using LISA, a comprehensive model of the tin can gun could be developed and the stress on each part predicted. The latching device for the tipped barrel might change or be refined at the time as a result of a more comprehensive analysis.
It would be a time-consuming project but fun for a retired guy. It’s probably unnecessary to mention that a “proofing” process would be part of the project. I should note that I never expected performance exceeding moment-of-garbage-can at five feet.
I should also note that, if I could get the weight down, it would not be particularly pleasant to shoot
P.S. Incidentally, “LISA” used a few of my analyses as examples on their website although they are not related to this project.