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Some images of the barrel of my pressure test gun. Not the best images -- the shop is quite a mess. After 20 years of procrastination and other priorities I think all that's left to do is shoot it. I've got the old Pressure Test System from RSI, and had to find an old computer (a Panasonic Toughbook!) with Windows XP to run it. Boy, is it ever clumsy to go back to those older versions of Windows. I'll shoot a few loads through it soon to check function, then load up about 100 each of what will be a couple of " comparison standards" at high and low pressure levels. I'll send some of each to Tom Armbrust or Precision Reloading to get their reading and hope then to correlate my rig to theirs and get some confidence my test gun will be useful. I strain gaged it down the barrel -- from breech face, 1", 2" 4", 6", 9" -- along the lines of what Sherman Bell did, and then I hope to determine maximum circumferential stress at those positions down the barrel. The immediate purpose is determining suitable smokeless powder loads for a certain damascus-barreled hammer 16.

Cheers!
Tony

Good luck! Hope it works at good for you!

Neat, good luck be on thee

Joined: 26 Apr 2010 Posts: 3313 Location: NCWa

It sounds like you are going to be shooting full loads, which causes me to where WHERE and into WHAT?

Joined: 30 Jul 2012 Posts: 356 Location: Central, ND

Very neat project. Just so you are aware you can use a PC running Windows 11 to run XP. You would need to install a software to use your current PC as a virtual machine to run XP. We do it all the time at work for some of our old equipment. Guessing you would need a USB to RS232/485 converter as well.

AmericanMeet -- Could you clarify your questions. What do you mean by "full loads", "where" and "what"?

I will attempt to correlate my test gun with "real" pressure test guns by the use of loads of at least 2 different, and hopefully widely-spaced, pressure levels, probably one near the SAAMI max, and one at maybe a 6000 psi level. A fairly large quantity of these "correlation standards loads" of exactly the same components, made by exactly the same methods/tools, and in the same batch, will be kept by me for future reference, if, for instance I change anything about my test barrel or the instrumentation thereof. I hope, by this method, to have a way to judge the suitability (safety and effectiveness) of loads for a particular damascus-barreled gun.

By the way, that damascus gun has 65mm chambers and bores of .662". It was my good luck to find a donor barrel for my test gun with the same chamber and bore dimensions. Yes, I know the fellows at the pressure test services don't credit any influence of shotshell cartridge length on the pressures they measure. That makes sense, as they are only concerned with peak pressures at about 1" from breech face. In my case, I'm concerned from the breech face all the way down the barrel, particularly at the 9" point which will be near my hand. Therefore, I'd rather have the chamber of the test gun the same length as those in my damascus gun.

One more thing I know someone is going to say -- "Why worry -- others are doing fine with light loads in damascus barrels." My barrels seem quite thin-walled on the breech end -- thinner than any others I've seen -- it's a very slim and dainty gun. The breech end is another bad place to have a failure. One thing I will investigate is the influence of hull rigidity on the stresses in the chamber area with loads of similar external ballistics. For instance, would I be better off using brass cartridges instead of these new-fangled paper and plastic hulls.

None of this removes the need for some sort of "proof test" of that damascus gun. However, once such proof test is done to my satisfaction -- hopefully not to destruction, but with considerable repetition at a reasonably high pressure threshold -- I will have developed a limiting pressure criteria for safe loads for that particular gun. This criteria will be more than the usual peak pressure at 1" from the breech face. It will also include tolerable pressures at positions down the barrel.

As to the where and at what questions, my pressure gun will be fired through a chronograph (the screens, I mean), down range at a safe barricade, same as any other ballistic test gun. If I use the gun a lot, I may eventually shoot it indoors, in which case I would need to devise a safe receptor for the ejecta, an exhaust system for gases and dust, and maybe some noise attenuation features. However, that cart is way before the horse, or another way to say it that might be more applicable to the case is that would be "jumping the gun". Laughing

Sorry, I crack myself up. Hopefully I won't crack my gun up.

Cheers,
Tony

Joined: 04 Mar 2019 Posts: 2180

Go for it Tony!!

Joined: 26 Apr 2010 Posts: 3313 Location: NCWa

Joined: 08 Feb 2009 Posts: 1554 Location: Western WA

Tony,

Brilliant approach and thinking. I am attempting much the same with the Pressure Test II system, sans Damascus barrel, with useful if not conclusive results to date. The PTII can run on Windows 10/11 albeit with some tormenting connection issues, hopefully resolved at this point.

I am not a Mechanical Engineer, but have a family member who is, and works with similar but industrial scale equipment, and who endorses the PTII methodology. My only reservation with your setup is Damascus barrels have different material properties than modern steel of your pressure barrel to which the strain gage measurements are calibrated. The PTII system has a remarkable ability to display the entire firing event at 10 microsecond (yes, microseconds) intervals over a 1.5 millisecond or longer ignition and firing sequence. My ME family member advises that not only the peak, but also the duration of the pressure pulse will affect the ability of the barrel to contain the forces. How the Damascus barrel reacts to the entire pressure pulse may or may not be represented by the steel in your pressure barrel. So be wary of extrapolating your pressure barrel data to damascus.

Also, with the dissolution of RSI, the support for software and limited hardware items has been very ably handled by John Schaefer (frfrog@centurylink.net).

All the Best,
B.

Member Joined: 06 Oct 2007 Posts: 2563 Location: West MI

Pretty neat interesting stuff, wish I lived closer and could hands-on participate but will watch here from the cheap seats. Thanks for sharing your progress.