Author Topic: Pressure testing - (Read 1815 times)

Cat Whisperer · « **on:** June 02, 2005, 12:37:05 PM »

We've all seen pressure testing pictures in Lyman reloading handbooks. Has anyone tried this to see what the actual pressures are on cannons and mortars?

It seems like we have an interesting collection of experiences and professions in this crowd and there might be someone that is doing it as a matter of course.

Short of that, does anyone have leads on the sources of pressure testing devices & materials AND sources on pressure testing standards.

SAAMI has a website, but not much free information (saami.org) - The Sproting Arms and Ammunition manufacturers' Institute.

CAV Trooper · « **Reply #1 on:** June 02, 2005, 01:00:33 PM »

CW,

On page 105 of The More Complete Cannoneer, it says a "test program was done in 1986-87 using a piezo-electric ballistics transducer to record time-pressure curves for a wide variety of blackpowder in a 3" Ordnance Rifle."

The results of those tests were published in a lengthy article in the Fall 1988 edition of the Artilleryman Magazine. Unfortunately NONE of the results were included in TMCC.

If there was some way to get a copy of that 17 year old magazine, I'll bet a bunch of our questions would be answered.

Charcoal · « **Reply #2 on:** June 02, 2005, 01:00:43 PM »

Hello,been a longtime lurker.I read the previous thread on materials.Here is something that has been on the market for years.Oehler Research,the chronograph folks,make the M43 and much more expensive M83 ballistic research systems that measure pressure.The M43 is $800.00 and while not for SAAMI specs does give pressure readings,better than guessing!!This may be something artillery makers,whether be cannons,mortars or gonnes should look into.Very nice projects on the board!!

http://www.oehler-research.com/

GGaskill · « **Reply #3 on:** June 02, 2005, 01:59:05 PM »

"If there was some way to get a copy of that 17 year old magazine, I'll bet a bunch of our questions would be answered."

Since the magazine is still published (by the publishers of Civil War News), I'll bet a letter or email to the publisher would get some results. But unless you are working with 3" bore pieces, I don't think there would be a lot of information that usefully translated to smaller pieces.

Cat Whisperer · « **Reply #4 on:** June 02, 2005, 03:30:39 PM »

Quote from: Charcoal

Hello,been a longtime lurker.I read the previous thread on materials.Here is something that has been on the market for years.Oehler Research,the chronograph folks,make the M43 and much more expensive M83 ballistic research systems that measure pressure.The M43 is $800.00 and while not for SAAMI specs does give pressure readings,better than guessing!!This may be something artillery makers,whether be cannons,mortars or gonnes should look into.Very nice projects on the board!! http://www.oehler-research.com/

Charcoal - WELCOME!!

Thanks for the reference. In the last hour or so since posting my previous post I ran across a related article ( http://www.oehler-research.com/wizard.html ) on the same instrument - very interesting reading indeed!

It has lead me to a dozen other articles and sources on strain gauges and hoop tensile strength measurement and calculations of applied stress.

There is a world of fun stuff to play with out there! I'm tempted to do some comparitive testing of 1018, 1144, 12L14 and 4140 cylindrical 'cannons' of say 1" or so diameter OD and varying ID's to see how they compare under 'normal' loads, 'proof' loads and destructive loads.

I also ran into a couple of sets of standards for testing procedures for destructive testing and determination of maximum charges that would cause destruction by EBWhite labs:

Test procedure - catastrophic testing http://www.hpwhite.com/101-00.pdf

The objective of these procedures is to identify the principal design features of a handgun, rifle or shotgun which could contribute to a firearm accident and put forth testing procedures which will confirm or deny the adequacy of the design features of a specific model of gun to resist those factors which result in firearm accidents. http://www.firearmsid.com/Feature%20Articles/022001/HPWhite.htm

Again, welcome, and post some of your pictures!

Cat Whisperer · « **Reply #5 on:** June 02, 2005, 03:35:44 PM »

Quote from: CAV Trooper

CW,

On page 105 of The More Complete Cannoneer, it says a "test program was done in 1986-87 using a piezo-electric ballistics transducer to record time-pressure curves for a wide variety of blackpowder in a 3" Ordnance Rifle."

The results of those tests were published in a lengthy article in the Fall 1988 edition of the Artilleryman Magazine. Unfortunately NONE of the results were included in TMCC.

If there was some way to get a copy of that 17 year old magazine, I'll bet a bunch of our questions would be answered.

It is exactly that type of testing that I've observed on the range with a fellow doing load testing on a .50 cal rifle - comparing the pressure curves (pressure - time) and the achieved velocities for a variety of loads.

Not too tough to do, takes some equipment though. Certainly worth the time to go to the range and do some comparitive testing.

GGaskill · « **Reply #6 on:** June 02, 2005, 08:51:11 PM »

We should keep in mind the following section from the H.P. White testing procedure preamble:

"1.4 Failure of a gun assembly from internal pressure may be from either of two (2) failure mechanisms.
"1.4.1 The general perception is that those failures are the result of a single exposure to a CATASTROPHIC PRESSURE level. This may be an over simplification in that the strength of the assembly may have been degraded by previous repeated exposures to excessive, but lesser, levels of pressure whose cumulative effect is to reduce the ultimate strength of the assembly.
"1.4.2 Repeated exposure to pressures which exceed the elastic limit of a material will continually reduce the ultimate strength of the material until the ultimate strength is exceeded by a relatively low pressure level causing fatigue failure."

Once a gun has left the elastic deformation stage, it is undergoing degradation. However, the degradation now becomes measurable with ordinary measuring devices as it is permanent, not transitory. So a good testing procedure will include continued measurements after the passing of proof until it is clear that there is no continuing dimensional change.

Cat Whisperer · « **Reply #7 on:** June 03, 2005, 12:34:11 AM »

Exactly right - hence good records and multiple measurements between shots.

Articifer Tom · « **Reply #8 on:** June 03, 2005, 01:46:46 PM »

You forced me to go in my libary of books and dig out my copy of the Artilleryman 1988 with what is nine paper report on the test in which they give lots of data ie. projectile weight , powder size , wadding , and even Pyrodex. But will not and don't want or draw any conclusions . There is also some info on other testing done about 1971` for NSSA. Also noted that article was written by Matt S.

GGaskill · « **Reply #9 on:** July 25, 2005, 02:05:12 PM »

I emailed Oehler on this subject and here is my email and their reply:

The internet cannon discussion group I monitor has gotten really concerned about the numbers of cannon making and we are interested in determining chamber pressure in black powder guns of various styles and materials. Would the M43 be useful for this? Thanks.

"The Model 43 that tests pressure using a strain gage has been used on black powder rifles. The problem you run into with its method of pressure testing is that the first thing you are to do after you instrument a barrel with the strain gage over the chamber is you are told to, when possible, fire some samples of factory ammo to see what kind of pressures the "factory ammo" produces in your barrel. When there is NOT any factory ammo, you are left with trying to come up with this "reference ammo" that would definitely be considered a "safe" range to work in with regard to pressure. We feel the pressure testing done with the Model 43 system and the strain gage does a very good job of showing relationships between different loads with regard to pressure differences. We also think it is a very good indication of what the pressure most likely is in the barrel instrumented with the strain gage if the user has input accurate numbers in the setup.

I know nothing about how a black powder cannon is constructed or what kind of pressures might be there. I can tell you that if there is a very thick barrel & low pressures, the strain gage will NOT work. A .22 rimfire does not generate a lot of pressure. Even in a "standard" barrel, the strain gage will NOT sense an accurate pressure unless the barrel over the chamber is "turned down" on a lathe so the chamber wall is much thinner than the standard chamber wall."

Looks like another approach will be required.

Double D · « **Reply #10 on:** July 26, 2005, 04:31:07 AM »

Quote from: CAV Trooper

CW,

On page 105 of The More Complete Cannoneer, it says a "test program was done in 1986-87 using a piezo-electric ballistics transducer to record time-pressure curves for a wide variety of blackpowder in a 3" Ordnance Rifle."

The results of those tests were published in a lengthy article in the Fall 1988 edition of the Artilleryman Magazine. Unfortunately NONE of the results were included in TMCC.

If there was some way to get a copy of that 17 year old magazine, I'll bet a bunch of our questions would be answered.

Back up one page to 104 in Switliks book and you will find a picture of crusher guage. Looks fairly simple to build. the discussion in the book isn't extremely detailed, but intersting none the less.

Cat Whisperer · « **Reply #11 on:** July 26, 2005, 12:10:17 PM »

There are also photos and diagrams of copper/lead crushers in the various reloading handbooks/cast-bullet handbooks.

The problem is where to start. Once you have built the device and selected a thickness of lead or copper - how do you calibrate it?

Double D · « **Reply #12 on:** July 26, 2005, 12:25:01 PM »

Quote from: Cat Whisperer

There are also photos and diagrams of copper/lead crushers in the various reloading handbooks/cast-bullet handbooks.

The problem is where to start. Once you have built the device and selected a thickness of lead or copper - how do you calibrate it?

CW,

There is a world of difference between the crusher gauges referred to in the rifle/pistol reloading manuals and the guage for the cannon. The cannon gauge gets loaded in the bore with the charge. I would think with a small amount of research the "crushability' of lead could be found. Probably here on the internet.

I also think a letter to MC Switlik would get you a barrel of info.

Cat Whisperer · « **Reply #13 on:** July 26, 2005, 12:32:54 PM »

Ahh yes. I'd forgotten that it was inside - a day or so had passed since I read about it.

That should be simple then - to calculate the pressure from the area of the larger 'piston' being pushed upon by the products of combustion and a known size of copper/lead pellet to be crushed.

Then the major difference between the measurement and that of firing without the device would be the offset produced by the change of volume in the barrel - with vs without the pressure measuring device.

GGaskill · « **Reply #14 on:** July 26, 2005, 02:28:05 PM »

For large bore artillery, the gauge is inside the bore. But I see no reason that a system similar to that used for small arms ammunition couldn't be used for smaller bore artillery, say anything under 3" bore. It would require making special test barrels for each configuration but not much else. And since we are really only interested in peak pressure, you wouldn't need a full length barrel or any of the decoration a model barrel might have.

I am going to try to find a source of crushers (both lead and copper) and get some prices, etc.

Double D · « **Reply #15 on:** July 26, 2005, 02:28:47 PM »

Since the crusher device sits at the back of the barrel up against the breech face at the back of the charge, I don't think in larger guns it's presence is going to be very significant.

I think the effects its presence on pressure would would be more equivalent to having a shorter barrel than a reduced volume. I think peak pressure would be reached before the projectile reached the muzzle.

Me, myself, I am just going trust Switliks charts and not load above that. Although pressure studies would be interesting.

Cat Whisperer · « **Reply #16 on:** July 26, 2005, 02:44:13 PM »

Quote from: Double D

Since the crusher device sits at the back of the barrel up against the breech face at the back of the charge, I don't think in larger guns it's presence is going to be very significant.

I think the effects its presence on pressure would would be more equivalent to having a shorter barrel than a reduced volume. I think peak pressure would be reached before the projectile reached the muzzle.

Me, myself, I am just going trust Switliks charts and not load above that. Although pressure studies would be interesting.

In rifles (smokless powder) the pressure peak is generally at or before the first inch of bullet travel. Probably not much different with black powder.

The difference, if any, with the measuring device would be if there was a powder chamber or a slight reduction in diameter to locate the ball a specific distance from the end of the bore. Then the device would alter the volume, hence change the pressure characteristics slightly.

There is a lot to be said about following emperically proven safe charges from a reputable source.

Terry C. · « **Reply #17 on:** July 26, 2005, 04:29:26 PM »

I finally got my own copy of TMCC.

Looking at the chart in Appendix I, some of the loads I've seen posted here are excessive according to Switlik.

My own 'pet load' of 250 grains in my 1.156" bore cannon exceeds the charted load by ten grains. This is a strong barrel and I have sufficient windage and don't use a patch, so I'm not worried. This barrel has been 'proofed' by 300 grain loads behind the 5-ounce ball several times. Still, I plan to back off to 240 in the future just to play it safe.

I stopped using the 300 grain load because of excessive recoil, turns out this was a wise decision.

If permissible, here are my observations of the chart as I near as I can read it:

0.500" = 40 grains
0.625" = 70 grains
0.750" = 100 grains
0.875" = 135 grains
1.000" = 180 grains
1.125" = 230 grains
1.250" = 290 grains
1.375" = 380 grains
1.500" = 500 grains

From: The More Complete Cannoneer by M.C. Switlik, Â©M.C. Switlik 1990.

(If it is improper to post this, please delete)

Double D · « **Reply #18 on:** July 26, 2005, 05:04:17 PM »

That book is an eye opener isn't. I think the information in it is worth twice the $24.50 it costs!

If you shoot cannons, big or little you should have this book.

GGaskill · « **Reply #19 on:** July 26, 2005, 05:07:34 PM »

Can you give the logic behind those numbers? 40 grains for a half inch bore, for example, seems absurdly low. Muzzle loading rifles are routinely charged with more than that using patched balls and their barrel walls are thinner than artillery barrels.

Terry C. · « **Reply #20 on:** July 26, 2005, 05:36:25 PM »

Don't know if that is based on pressure or practicality.

I've shot small-scale cannon (.45-.50) and the recoil makes loads derived from BP sporting firearms impractical. The guns are just too light.

That's why I went 1/4 scale with my current gun. It's big enough to be somewhat realistic in the way it handles recoil.

Double D · « **Reply #21 on:** July 26, 2005, 05:45:20 PM »

Aha, you don't have the book!

He is taking those figures from the chart in Switliks book and the recomended charges for miniature cannons. Bottom line you don't need the heavier charges in a cannon. Since I have been shooting loads from his chart, I can see the difference in performance. It als appears that my gun is less violent when shot. Much easier on the equipment.

How Switlik arrived at those figures? Maybe a letter to him will get the answer.

GGaskill · « **Reply #22 on:** July 26, 2005, 08:00:37 PM »

I realize where he got the numbers from; the question was how the numbers were derived by Switlik (assuming that was included in the book.) I load about 220 grains (1/2 ounce) in my 1 inch bore and chambered pieces.

Of course one can load under maximum loads for whatever reason one has. I was interested in how "maximum" was determined and whether there was a scientific (versus semi-WAG) basis for the numbers.

Cat Whisperer · « **Reply #23 on:** July 27, 2005, 12:32:47 AM »

One has the same dillema with a cannon and maximum load that one does with a submarine and maximum safe depth.

Same issues. How do you test it without destroying it. How do you KNOW!?

We've all (or most of us anyway) 'gotten away with' heavier charges than what should have been used.

Double D · « **Reply #24 on:** July 27, 2005, 02:32:17 AM »

I suppose if you "hafta" know you could drop Switilik a letter...

GGaskill · « **Reply #25 on:** July 27, 2005, 08:02:16 AM »

"One has the same dilemma with a cannon and maximum load that one does with a submarine and maximum safe depth.

Same issues. How do you test it without destroying it. How do you KNOW!? "

The difference is that the sub designers know what the water pressure is at any given depth and can do the math to determine how a design will react to that pressure. In our case, the chamber pressure is the thing we do not know and therefore doing math is irrelevant since we don't know what forces we are trying to resist. And unlike water pressure, chamber pressure is a function of chamber dimensions, powder type, granulation, charge weight and projectile weight plus a number of lesser factors. So without determining the chamber pressure for the specific combination of factors we are using, we are left quoting numbers generated from more or less (mostly less) similar experiments.

Besides, the maximum SAFE depth/load is one that gives a safety factor that allows for minor errors without causing catastrophic failure, not one that is one foot short of crush/one grain short of bursting.

Double D · « **Reply #26 on:** July 27, 2005, 10:45:11 AM »

Quote from: Double D

I suppose if you "hafta" know you could drop Switilik a letter...

Boy that is a sarcastic reply...It sure wasn't intended to be, my apologies.

If you do write Switlik an ask how he came up with his chart, please share with us.

GGaskill · « **Reply #27 on:** July 27, 2005, 11:36:05 AM »

Didn't interpret it that way, nor was my replied intended in that tone, either.

One of the downsides of electronic print communication is the loss of vocal intonation that carries that kind of information.

Cat Whisperer · « **Reply #28 on:** July 27, 2005, 12:05:53 PM »

I certainly didn't take any offense.

We are dealing with a lot of variables here - moving from formulas and theory into real-life practice.

Overbuilding and wide safety margins certainly in order, until one can do (at least some) testing of the design with known materials.

guardsgunner · « **Reply #29 on:** July 27, 2005, 01:59:25 PM »

I've not read Switilik's book.
Wasn't the testing brought about by the quality of some of the castings and the manner in which some of the casting were being done.(pipe core)As on a small gun with the liner way off center discussed a couple of months ago here.
didn't this lead to the steel liners that are now required?
From the load chart
A model .50 cannon would have more mass at the breech than a rifle of the same cal. yet I don't know anyone who shoots as light as 40 gr. except in civil war carbines which do not allow that much due to cartridge capacity. Same goes for .69 which start at about 80gr. and go to about 110.

Is it possible that some of the information has been taken out of context?
Was it for castings?
One other thing to note here is that Switilik also is the host for the Grayling shoot which sports all full service charges that shake the ground..