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357 Pressure Barrel Part III

Posted: Sun Apr 12, 2015 4:49 pm
by mtngun
I finally put a strain gage on the Green Mountain 357 Contender Barrel with the Eagle Arms stub.

I wasn't happy with the gage installation for a variety of reasons. I used a 6 year old tube of superglue, and it didn't seem very sticky to me. Superglue has a shelf life so you are supposed to use fresh glue, but this was all I had on hand at the time.

Then I unintentionally got superglue on the connector. I had to reseat the cable multiple times before it would make contact.

And then the way the cable was routed was not ideal. So all in all, I was not happy with this particular installation.

Then there is the question of whether the strain gage will even work correctly with a barrel stub. If the stub threads are a loose fit, that is bound to mess up the expansion of the stub when the cartridge is fired. But I strove for a tight fit on the threads, and used lots of anti-sieze with the hope that it would fill any gaps between the tenon threads and the stub threads.

Anyway, here is the result, with no tweaks to the data. The good news is that the average peak pressure is about 35,000 psi, about what a 357 mag should be. The bad news is that it is extremely noisy data to the point that it's not very usable.

I'm not sure whether the noise is due to the stub, or due to the not-so-great gage installation? We'll see if the noise problem shows up on the next stubbed barrel that I put together.

Re: 357 Pressure Barrel Part III

Posted: Wed Nov 09, 2016 2:29 pm
by Irishtexan
Can you glue the strain gauge in front of the barrel lug just in front of the frame so your on the barrel and not the stub and get a accurate reading, just thinking out loud.

Re: 357 Pressure Barrel Part III

Posted: Wed Nov 09, 2016 4:44 pm
by mtngun
Yes, you could do that. It would read the barrel pressure at that point, but not the chamber pressure. It would not see the start of ignition & engraving, but it would provide a signal that could be used for relative measurements.

I haven't had time to focus on the pressure barrel lately, but decided the stubbed TC was not the best way to go. Either I need to tool up to weld a lug onto a solid barrel, or else abandon the TC altogether and find some other type of action to use for pressure measurement.

One thought is the Lone Eagle rotating breech? It doesn't take up much room on the barrel.

Or perhaps a falling block with a short barrel tenon?

Bolt guns work well enough with a strain gage on long cartridges like the 30-06, but not with short cartridges like the BR's or the 357 mag. Besides, there aren't many bolt guns for the 357 mag.

Too many projects, not enough time. :lol: