Re: Pressure Tesing Equipment
Really good engineers would ask you what you really want to do over and over until they wear you down.
I am just an average guy.
I will tell you that if I bond CEA-O6-250UW-350 strain gauges and AD8554 op amps in an instrumentation amplifier configuration, I can get great accuracy in measuring the strain on barrel steel locally. The stress to strain slope is fairly constant and known.
But there are some gaps in the process where the meaning of measurements get lost:
The measured strain to pressure relationship depends on the shape of the barrel and the location of the the gauge. The shape will have to be interpreted through Roark's book. The pressure in PSI has no real meaning other than what was capriciously registered at SAAMI.
Any one of those is a deal killer:
1) You don't know the barrel shape with accuracy.
2) You don't know the mathematical interpretation of the barrel shape to stress transform with accuracy.
3) You don't know the location you bonded the gauge on the barrel with accuracy.
4) Measurements in PSI have no meaning other than some SAAMI number.
If the pressure testing has no meaning, what does?
In a strong rifle, brass life has meaning.
You want to work up to the threshold of short brass life and back off a safety margin ala Vernon Speer 1956.
Who would use this pressure measuring stuff?
People who sell ammo need to do something, but the calibration process they use is not traceable to the NIST, but melds into a consensus.
Is there any harm in putting a strain gauge on my rifle for personal use?
No, as long as precautions are taken not to become smug with relative measurements as if they were absolute.
How can you make sense of this?
You can go to the other side and read Denton Bramwell or Ken Oehler and see if what they say circumvents what I say or vice versa.
Or you could ponder this joke:
Why can Baptists make love standing up?
Because it looks too much like they are dancing.
What does that joke have to do with pressure measurement?
The 1905 8x57 Mauser did 2900 fps with 150 gr.
That is at the threshold of the brass yield minus a safety margin.
104 years later you are using a Mauser case head design in your 308.
The 308 is registered at 60,000 psi to get it close to the yield minus a safety margin. To measure the pressure instead of looking for yield and backing off a safety margin is to introduce error, cost, delays, and extra equipment. But rules are rules and must be followed. If dancing might lead to sex, then sex cannot be done that looks like dancing, because that might lead to sex. Pressure must be measured to avoid brass yield, because brass yield looks like pressure that is measured at the threshold of brass yield.
