doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Strain gauges

William, I suppose anything is possible, but I have a difficult time imagining on what theory a real successful legal action would be based. You have included gobs of disclaimers. You haven't charged for services. You have not named yourself an expert.

Lets say I offered someone directions that required crossing a railroad track. Am I liable if they walk/drive in front of a train?

Personally, I hope you do keep posting. I like your work.

William, There are much bigger things in this world to worry over.

You have a device that consistently and reliably measures something. Nothing more. It does exactly what it's supposed to do.

As I said in my first post within this thread, it is a mistake to use the data to improperly extrapolate an answer to a different question.
You, or anyone else in the world with a yardstick, cannot be held responsible for what someone thinks is meant by a measurement.

You need to ease back on the paranoia throttle a bit.

My view on these pressure measurers is they are a great QC tool.
For ammunition.

Bill,
I can't imagine anyone would think they could make a claim against a name on the internet that posted something, let alone be successful. The whole internet couldn't exist if these people were right.

Don't let some twit comment rob you of exchanging experiences here.

Personally, I'd like to see you post more.

Regards
Chuck

Rocketman, you've left me in a state of confusion. The wad moves down the barrel. The strain gauge only measures pressure where it's placed--typically in the chamber, to measure peak pressure. Are you then saying that the peak pressure remains the same all the way down the barrel--as long as it's measured behind the wad? I don't think that's what you're trying to say, but what you are trying to say is unclear to me.

The only point Bell was exploring in his tests was whether fast vs slow powders (black included in the latter) had a significantly different pressure profile, and especially whether slow powders peaked significantly farther down the barrel than fast powders. His tests established that all powders reach their peak pressure inside the chamber. Nothing he did in that test, or attempted to do, had anything to do with selecting the correct load (which would include primer, wad, and shot charge as well as powder) to result in a pressure low enough to be within the parameters for which specific barrels were designed.

LB,
My take on Don's point was that pressure is distributed equally in the available volume at any instantaneous point in time during the acceleration of the payload. So, if you measured strain/pressure 1" from the breach, at a particular time in the firing process, the pressure would be the same at that time from the breach to the point just behind the wad base. If a payload was halfway down the barrel, the pressure behind the way would be the same as at the breach, at that particular time. There may be some gas dynamics that aren't accounted for in this conclusion, but it should be reasonably close. The Pressure Trace will, with a single measurement point at the breach, measures pressures for the entire trip of the payload down the barrel. It is depicted in a pressure/time curve. Figuring out exactly where the payload is along the barrel is tougher. Bell's setup of testing at ports along the barrel eliminated the job of figuring out where the payload was along the barrel at any given time.

My understanding of Bell's multi-port testing was to see if peak pressure occurred and/or higher pressures were maintained with the payload significantly further down the barrel when using slower powders than with faster powders. This was a theory that, if true, could expose thinner areas of the tapered barrels to higher stress than might be safe. It would not neccesarily have to be peak pressure that ruptures a barrel in the thinner sections further down the barrel. Just pressures that exert higher stress than that section of the barrel can take. I'm guessing we have the same understanding of what Bell was trying to reveal.

Now I'm seriously confused. There's only one pressure peak, after which pressure drops. Only goes one direction after the peak, which is down. You talk about "the decay in pressure" while also referring to "peak pressure at each location from chamber to muzzle". Those two concepts directly contradict each other. Peak, as an adjective, means highest--and there can be only one highest. Everything else is lower. You also have contradictory statements about pressure measurements. You agree that the gauge only measures pressure where it's placed . . . but then you tell me it measures pressure all the way down the barrel. If it did that, then why did Bell use several strain gauges? And I thought we'd agreed previously that a strain gauge depends on the dimensions of the metal--which obviously change significantly from chamber to muzzle, which would make it impossible for a single gauge placed in the chamber to measure pressure at the muzzle, where the dimension of the metal is very different.

Waters are getting murkier and murkier . . .

Larry;
Go back & re-read R-man very slowly & carefully. You're not quoting what R-Man said at all. The Strain gauge does indeed only measure the pressure at one point. It is set at about the 1" point to be sure & catch the peak. Yes it only occurs once, that's exaxtly what R-Man said.

You are I think confusing these gauges with the action of a crusher which can only measure the (1) peak. The strain gauge on the other hand gives a continous reading of the pressure in the bbl. As the shot moves on down the bbl, the pressure falls (Decays) & it does so over the entire length from breech to wads at a basically even pressure. Thus while if a load peaks at 9K for instance 2" from the breech, this is the only pressure which a lead crusher will record, even though at the 6" point the pressure may be only 4K & will also have that amount of pressure now at the 2" point as well. The Strrain gauge on the other hand will record both the 9K & the 4K pressures & give the "Time" they occured.

Bell could have gotten very accepctable results with the use of only one gauge. He could of course have simply read the Cox/DuPont results which had been on record since the early 1920's & had adequantly proven & recorded what he was trying to determine. These tests were I believe done using Piezo Electric gauges which were also capable of reading continous pressure curves.

If you will just go back & comprehend R-Mans posts you will see they are not contradictary at all but straight forward & quite easy to understand. The absolute "Peak" pressure was of course reached only once. The "Peak" at any point beyond did not reach the same pressure as that high point of the entire bbl, but was the peak for "That Point". Thus from my above scenario the bbl peak would have been reached at 2" @ 9K, but the peak at 6" was 4K, the pressure never reached 9K @ 6" from the breech. A strain gauge set at the 1" point would have shown a reading of 9K when at the 2" peak & 4k when the wad passed the 6" point as the pressure would have been equalizing all along the bore as the shot traveled down it. The pressure did not stay at 9k at the peak point for the entire time the shot was in the bbl.

If you put a pressure gauge on the valve stem of a tire & it reads 32psi, & you then go half way around the tire & stick an ice pick in & yank it out as you hear that hissing sound the pressure will start to drop at the valve the same as it does next to the puncture, it'll go flat all the way around. The one gauge will read the pressure in the entire tire, just as that one strain gauge will read the pressure in the entire bbl.

Miller, from my reading of Cox you are correct. They were only "handicapped" by not having a digital oscilloscope. However, by increasing the dwell the trace stays visible for some time. They would photograph the trace. Using the photo, they would then hand copy each result to a paper graph. At least that is the presumed method. Cox never gives exact detail except to note the use of piezo gauges.

Pete

Stay the course and it will become clear. I've faith in you, good buddy, faith, I say!!

Thanks, 2-p. A very good explaination and exactly on point. I had, however, written the above before I read you reply - - - so, why waste a lot of good key strokes!!

Pete, I think you are exactly right as to Cox's method. I used a similar method with a scope equipped with a Polaroid camera in an undergraduate research project. Upon graduation, I was soon "awarded" a 10 channel light oscillograph (you had to photgraphically develop the paper) for tire traction studies.