Barrel Pressure - GolfBall Parrott Cannon

[Parrott-Cannon]

I purchased a Pressure Trace II system.  The attached pressure graph was obtained on my Golfball Parrott Cannon - powder charge 400 grains cannon grade powder - Golfball for ammo.  Meassure Muzzle Velocity - 688.7 fps.  The maximum pressure was 38,019 PSI.

A blank shot produced over 5000 PSI

Be carefull!

The Pressure Trace II system is designed for highpower rifles.  The company was been very helpful and I am pleased with the system.

John

[Soot]

You will be able to do a lot of interesting testing with that.

[Victor3]

 Interesting. I wouldn't have thought the pressure to be near that high using a golf ball and cannon grade.

 A while back, someone said that they had contacted the company that makes the Pressure Trace systems (or maybe it was a similar setup from a different company?) and was told that it wouldn't work well on a BP cannon. I assume they must have told you different regarding this application?

[Artilleryman]

If memory serves me correctly, when we did the pressure testing on an Ordnance Rifle using service load they didn't get that high.

[Cat Whisperer]

I would like to know how it was measured and what the windage was.

[Double D]

I have the same equipment, but never considered setting it up on a cannon.  http://www.shootingsoftware.com/pressure.htm

What Makes It Work
The PressureTrace system consists of a microprocessor control module, cables PC software and a strain gage. The control module is connected between a strain gage (glued to your barrel) and a PC (not included) via bluetooth wireless connection. The PC runs software which emulates an oscilloscope and provides analytical tools. If your computer does not have bluetooth, inexpensive dongles are available that will add a bluetooth radio to any USB port.

A strain gage is simply a small piece of polymer material with a fine conductive grid on its surface. As steel around the barrel expands the gage is stretched and current flow through the grid is altered. The PressureTrace module samples these current fluctuations (1 sample per 10 micro seconds/350 per shot), stores it in a memory buffer, then automatically downloads the raw data to the PC via a wireless connection where it is analyzed and plotted. Up to 10 shots can be overlayed and compared on screen at a time.

[Cat Whisperer]

Good overview.

Knowing a LITTLE about sensors, I'd like to see how the strain gauge was attached and to know something of the accuracy with different diameters;  that is how it was calibrated. The strain gauge is going to measure the amount of flexing and predict by formula the stress (pressure) applied.  Does the material make a difference?  I would think so - some metals will flex more than others for a given pressure.  Just asking to understand the specific process and not to make assumptions.

Still the questions of windage.  I would think that a patched round would produce much higher pressures than one with windgage, but that is a supposition.

[seacoastartillery]

     39,019 pounds per square inch???  Call me a skeptic.  It might be helpful if you check your new equipment out on a known pressure firearm and a cartridge such as the .308 Winchester.  Please let us know how it goes; we have appreciated your posts in the past on cannon ballistics.

Tracy and Mike

[Victor3]

     39,019 pounds per square inch???  Call me a skeptic.  It might be helpful if you check your new equipment out on a known pressure firearm and a cartridge such as the .308 Winchester.  Please let us know how it goes; we have appreciated your posts in the past on cannon ballistics.

Tracy and Mike

 That might not provide useful info regarding large cannons if the unit is designed only to be used on a range of small diameter barrles.

 I have the same questions as CW. What info does one feed the computer to ensure data from the sensor is interpreted correctly?

[seacoastartillery]

     Just more proof that you can Never Assume Anything.  I mistakenly assumed that everyone would know that our intent was merely to check and see if the new pressure tester was functioning properly.  That's it.  That was the only purpose I had in mind, nothing at all to do with cannon pressures at all.  From that baseline measurement you can develop a whole series of tests which focus on black powder firearms and cannons in particular.  Perhaps, as some have suggested, this equipment simply will not work for BP cannons and the typical low pressures they develop.

Tracy and Mike

[Double D]

If you are skeptical and question the viablity of the equipment I suggest you read the description posted at.   http://www.shootingsoftware.com/pressure.htm.  You may find your questions answered.

This system also reads PSI and not CUP's.

[Cat Whisperer]

If you are skeptical and question the viablity of the equipment I suggest you read the description posted at.   http://www.shootingsoftware.com/pressure.htm.  You may find your questions answered.

This system also reads PSI and not CUP's.

Not skeptical.  But I don't yet see the formulas used and the assumptions made, just a statement about using thick and thin wall open vessel algorithms.  Which ones?  Calibration is done to a known standard load - but in which gun?  To me calibration includes both an offset value and a scaling factor.  A minimum of two known measured loads are compared.  Then ASSUMING linear relationship the slope and intercepts can be calculated.  THEN you have an instrument that is calibrated in comparison to a known measurement system.  Other than that, one makes some good-guess assumptions and uses some prety good formulas that will put one in the ballpark and live with it as being reasonably close given the list of assumptions made.  I simply would like to know what they are.

[Parrott-Cannon]

First:  Sorry about not getting back on my post but my wife fell and broke her foot right after I made the post.  Emergency room and operation to pin 3 fractures.  Been doing double duty on chores and have not had time to reply.

I have used the pressure trace on my Browning rife and it produces the published results.  Therefore the instrument is ok.

I did a theortical calculation on the ordance rifle data - 16400 psi with 7000 grains cannon grade powder and a 80062 grain projectile vs my Parrott cannon 400 grains of powder and a 700 grain projectile.

The result - the Parrott rifle should have experienced a pressure of 5700 psi.  I examined the sensor on the Parrott and found the bond to the barrel had broken at one end.  This will cause extra flexure in the sensor and therefore higher reading.

I did use all the appropriate factors for the type of metal, this must be entered in the Pressure Trace software prior to operation.

 

[Cat Whisperer]

First:  Sorry about not getting back on my post but my wife fell and broke her foot right after I made the post.  Emergency room and operation to pin 3 fractures.  Been doing double duty on chores and have not had time to reply.
I have used the pressure trace on my Browning rife and it produces the published results.  Therefore the instrument is ok.
I did a theortical calculation on the ordance rifle data - 16400 psi with 7000 grains cannon grade powder and a 80062 grain projectile vs my Parrott cannon 400 grains of powder and a 700 grain projectile.
The result - the Parrott rifle should have experienced a pressure of 5700 psi.  I examined the sensor on the Parrott and found the bond to the barrel had broken at one end.  This will cause extra flexure in the sensor and therefore higher reading.
I did use all the appropriate factors for the type of metal, this must be entered in the Pressure Trace software prior to operation.

A) You have your priorities RIGHT!  Take care of family FIRST!    Better a break than a sprain - heals better; wish y'all the best.
B) Good info on your follow up - THANKS!   I have a friend that used to teach a course on estimation - a good practice to do in life, to do a reality check on what numbers the computer spits out - or the cash regiser - or the credit card machine. 

[Victor3]

 P-C,

 Sorry to hear about your Wife's accident. My Mom fell off a stool about two years ago and nearly bled to death when her fibula snapped and cut to the outside of her leg. No fun.

 It will be interesting to see the graph when you get time to do the test again.

 I was amazed at this one; never thought a firearm could produce such an odd spike after the bullet is out of the bore...



 Hope there's no way something similar could happen in a BP cannon.

[GGaskill]

I saw that and wondered the same.  I would like to see the same gun/cartridge fired using someone else's instrumentation that produced the same curves.  Hard to believe the pressure inside the barrel could reach that high without constraint, especially that far along in the burn.

[VA Rifleman]

If I put my instrumentation hat on, the sensor is "flat lining". at the top of it's range after the bullet has left the bore.
Free floated barrel?  Probably all wet but those late peaks remind me of my heavy barrel .22 Anshutz 1411 that vibrates very subtly like a tuning fork after being fired. Most accurate rifle I own.

[Soot]

I was thinking barrel whip might produce that spike, but that's just a WAG.

[Victor3]

I was thinking barrel whip might produce that spike, but that's just a WAG.

 Could be, but their 'tech article' on the secondary pressure events they're seeing indicates that they don't think so...

http://www.shootingsoftware.com/barrel.htm

 However, note that some of their prime evidence that it's not whip/harmonics is...

 "In an attempt to prove this theory one shooter even hung a bowling ball off the end of his barrel..."

 And...

 "Charley Sisk at Sisk Rifles blew the end off two barrels."

 Hardly scientific 'Proof Positive.'  

 Their "Catch Up" theory makes the most sense to me if the spikes are indeed caused by elevated pressure. I can see how unburned powder might be blown out of the case and then burn when it's further down the bore. But IMO, how much pressure that could actually create is anyones WAG.

 Check out this graph for a .223...



 If events like this are not rare (as the authors of the article seem to be claiming), I assume we'd see quite few more unexplained banana-peeled, thin-wall barrels over the years. Since that's not the case, I'm a little sceptical that the data they're recording is actually due to pressure.

 On top of that, remember that these spikes are recorded by the strain gage attatched to the chamber area of the barrel, but they are occurring at a point in time when the bullet is near the muzzle or even after it's out of the bore.  

 As far as how these pressure spikes (if they're real) could possibly relate to BP cannons, I don't know. The way BP burns is so different than smokeless.

 If one were to have a long, fairly thin-walled barrel with an extra long powder chamber, some of the powder might blow out of the chamber and burn in the bore, causing a pressure spike in the thin-wall area. Maybe...

[GGaskill]

Something that seems strange about that last set of curves is the pressure is so low at bullet exit after reaching the high point they are claiming.  I am wondering if the strain gage is separating from the barrel and not accurately measuring the barrel expansion but something else.  They say the connections are soldered to the gages in advance (Oehler says to solder them after the gage is glued to the barrel) and I wonder if that prevents a good connection of the gage to the barrel so that they are measuring distortion of the gage caused by the wires instead of the expanding barrel.

[Victor3]

 Who knows. Elastic hysteresis due to the adhesive might cause a lag in when the sampling occurs. I don't imagine the software can correct for that very accurately.