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Thread: pressure test device for new loads

  1. #1
    Boolit Master

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    pressure test device for new loads

    does anybody have blueprints for a 12 gauge test gun that allows a person to come up with their own recipes safely. down the road I want to experiment with shorty slug loads but want a controlled way to check pressures.

    if all you can say is its to dangerous and foolhardy than don't comment but if you have positive ideas or have done something like this I would love to hear about your trials and tribulations. just something I would like to experiment with but I do want it to be under a safe environment.

  2. #2
    Vendor Sponsor uncle dino's Avatar
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    There are strain gauges available.. You epoxy sensor to barrel and hook to computer.. D

  3. #3
    Boolit Master

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    Don't have plans but the old system used lead or copper cylinders as "crushers". Gas pressure pushed on the crusher and would cause it to yield. Micrometer measurements told the tester the change in dimensions which gave an approximate pressure. Not exact but comparative and repeatable. Things do have to be accurately machined though.

    Not sure if crusher dimensions and the system designs are readily available but you could certainly make your own and use factory rounds as a benchmark. You'd want a beefy barrel and breech system then the rest is pretty easy I think.

    There are pictures in one of my shotgun manuals... probably one of the Lyman manuals.

    The strain gauge system is good and probably more accurate. Not sure of the strain gauge attachment requirements and usage though. If the strain gauge stays attached for multiple shots then that has to be easier than the crusher system but likely much costlier to get equipment. You can make a crusher system if you have a few tools but strain gauge system, not likely.

    You might ask Larry Gibson as he has a strain gauge system.

    I've thought about this myself but not gone ahead. I will be watching for developments!

    Longbow

  4. #4
    Boolit Master

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    thinking I may need different length exchangeable barrels to better check performance, or am I overthinking things.

    look forward to hearing from larry, he usually can explain things in simpler terms.

  5. #5
    Boolit Master

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    I doubt you'd need different length barrels. Breech pressure isn't going to change... unless you are thinking maybe a 6" long barrel? Then maybe. I'll bet peak pressure is reached before the payload is 12" down the barrel. Longer barrel will certainly affect velocity and possibly groups for shot.

    Yeah, Larry will know for sure, and how much trouble epoxying is and what the cost of the equipment is. I think that is the biggest hurdle for most. I believe several thousand dollars is the answer and I'm pretty sure it is more than I want to spend.

    Have you PM'd Larry? Not sure he frequents the shotgun forum. He is more of a rifle and handgun guy... I think.

  6. #6
    Boolit Man
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    Quote Originally Posted by longbow View Post

    Yeah, Larry will know for sure, and how much trouble epoxying is and what the cost of the equipment is. I think that is the biggest hurdle for most. I believe several thousand dollars is the answer and I'm pretty sure it is more than I want to spend..
    The RSI Pressure Trace 2 system is more like $600, with extra strain gages another $100 or so. I'll vouch for how annoying the epoxying is, it is what de-railed me using mine earlier this spring, then other chores caught up and I haven't had a chance to re-start my familiarization (I need to do quite a bit of familiarization before I do much experimentation).

  7. #7
    Boolit Master


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    I have pressure tested loads in a 410 single shot shotgun using a strain gauge and the Oehler M43 PBL.

    Easy enough to do with other shotguns. However, the strain gauge is "permanent" so to speak as the bluing is removed and the area completely degreased and lightly etched with a mild acid at the location before the gauge is super glued and epoxied to the barrel. With rifles I can usually affix the gauge to the bottom of the barrel so it is hidden by the stock. On other firearm types that's not possible. Applying the gauge to the barrel is a process but following directions it is not difficult. Also they can come off for various reasons.

    Additionally some protection of the screens, mostly from the wads, must be made and used.

    As to shotguns; older single shot guns will be the easiest to use.
    Last edited by Larry Gibson; 11-13-2017 at 09:56 AM.
    Larry Gibson

    “Deficient observation is merely a form of ignorance and responsible for the many morbid notions and foolish ideas prevailing.”
    ― Nikola Tesla

  8. #8
    Anything like a conventional shotgun load will have fallen far below peak pressure long before the twelve-inch mark. That is why shotgun barrels have such an extreme and normally concave taper.

    Here is a very interesting table, heavily interpreted by myself. It originated in the work of a Captain Noble (not Nobel), but was reprinted by Sir Gerald Burrard, whose three-volume "The Modern Shotgun", although dating in revised editions from the 1960s, I think is still the best in his field.

    Click image for larger version. 

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    The third column shows the pressure, in 2,240lb. tons) which would be obtained if a barrel were totally blocked at certain distances from the breech-face. (This is for a powder which doesn't exist any more, in a 2˝in. chamber, and shot striking an obstructed bore behaves very differently, so don't try this at home.) The last three columns don't necessarily show bursting pressures. They show when the inner layers are stretched beyond their elastic limit, but if this causes them to be more tightly constrained by the outer layers, the principle known in artillery as frettage. (I at first typed "frottage", which is something dirty old men in crowded buses get locked up for.)

    The astonishing thing is that pressure alone, ignoring the effect of shot striking an obstruction, appears incapable of damaging a barrel in even fairly mediocre steel, at more than four inches from the breech face. Most shotgun bursts are caused by bore obstructions, and most of those that aren't are caused by a barrel locally impaired in some way, either built-in in manufacture or by subsequent abuse. "Locally" is an important word. Just as a notched fishing-rod can break there rather than where it tapers to the same thickness a few inches further on, a deep pit can be more weakening that a paper-thin but bright bore.

    I have seen a device described, about fifty years ago, which so far as I know has never been marketed. It depelds on the fact that most shotguns have enough free headspace to insert a thin head-sized shim. Two dies are given a coverage of very fine circular grooves, so that they interlock, crests in roots, when the dies are pressed together. They are then used to press tiny sharp corrugations into a piece of heavy metal foil, possibly of around the thickness used to close coffee cans. When you fire a cartridge with this behind the head, the grooves will be part-way flattened out.

    This gives you a good comparison with a load you know to be safe, not a numerical measurement. But that is all you get with a crusher gauge, unless you know the mathematics and are very sure of the composition and hardness of your copper or lead. For a shotgun lead is better than copper. You just might be able to make a device small enough for a shotgun, whi ch imitates one sometimes used in artillery. This is a separate crusher cylinder actually incorporated in the powder charge. The gun doesn't have to be modified, but you feel a fool if you lose it. A water tank with a plastic membrane entrance might be best.

  9. #9
    Boolit Master

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    had not considered a regular barrel, I was thinking it had to be a massive chunk of metal, this may be simpler than I thought. how many times can the strain gauge be used. anybody got a photo of a commercial version they would share.

    thanks everybody.

  10. #10

  11. #11
    Boolit Master

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    Well, looks like prices have come down some to say the least. At least since I looked last but then I'm getting old. This sounds more doable at that price and way easier than crushers.

    If I was doing the crusher system I'd use a beefy "barrel" for sure just because but the strain gauge system is so much easier and if prices are that low cheaper as well, unless the crusher system was made from scratch and you discounted your labour.

    Yes, simpler than I thought too.

    Can anyone point out inherent dangers? Like as long as you start with "reasonable" powder charges and work up slowly are there any pitfalls a guy might encounter? I'm thinking like the issues with very slow rifle powders at light charges or powders that maybe respond somewhat unpredictably. Probably not a big issue with shotgun powders as they are relatively fast and always compressed, just wondering.

    I'm guessing Quickload or similar is the best way to get starting loads?

    Sorry, not trying to hijack your thread but I'm interested too.

    Longbow

  12. #12
    Boolit Master


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    Quote Originally Posted by rancher1913 View Post
    had not considered a regular barrel, I was thinking it had to be a massive chunk of metal, this may be simpler than I thought. how many times can the strain gauge be used. anybody got a photo of a commercial version they would share.

    thanks everybody.
    I have fired thousands of rounds through several different test barrels. The gauge, once affixed to a barrel is permanent. If it is removed or comes off for any reason it can not be used again. Last time I bought gauges they were about $15 each. Probably $20-25 now.
    Larry Gibson

    “Deficient observation is merely a form of ignorance and responsible for the many morbid notions and foolish ideas prevailing.”
    ― Nikola Tesla

  13. #13
    Boolit Master

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    longbow your not hijacking anything, thats good thinking and the more we discuss this the better and safer I will feel when I start this project.

    my goal is to make slug loads as short as I can and still cycle in a pump action, hopefully with only slight modifications to readily available cheep components.

  14. #14
    Boolit Master

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    thanks bk7saum, that is a great site.

  15. #15
    Over $150 for an outdated computer program? Wow, talk about a monopoly. I'd rather pay $600 for RSI pressure trace, but that's just me.

  16. #16
    Boolit Buddy
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    What I found with the RSI Pressure Trace is that replacing the Loctite 401 provided with Bison Epoxy Universal (two-part) strain gages are much better attached on barrels.

  17. #17
    Boolit Master


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    Pressure is pressure. Putting a strain gauge on an old beater single barrel will give you the info you want without affecting the cosmetics of a gun you care about. Strapping the gun to a tire and a long string for the first shot may be prudent.

    Doing it right may cost a bit, but shotguns are easy to blow up. Some of the slug loads posted here and on other sites have no published reference.
    Don Verna

    NRA Endowment Member

  18. #18
    Boolit Master
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    Remington 870 test to destruction.

    http://www.shotgunlife.com/shotguns/...pressures.html

  19. #19
    Boolit Master

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    don that tire idea is sort of what I had in mind but probably more along the lines of a range vise, I do not plan on deliberately blowing up a gun but rather ladder up to a load that is safe and can be proven to be safe several times.

    please keep the ideas coming.

  20. #20
    Boolit Buddy
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    Maybe a Savage 212 with a heavy barrel, chambered and bored at minimum (pressure barrel) dimensions would qualify.

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