Proof Testing barrels

[KABAR2]

Brought up on another thread was talk of proof testing a barrel

by a double charge of powder and two round shot as a proof load,

someone else said it was that one barrel would be tested as proof that the

design was sound and those made after it would be fine, he stated that

proofing barrels on production guns could damage or over stress them.

This is in error, while the U.S. does not have a government mandated "proof house"

manufactures proof their barrels, England,Germany France, Switzerland Italy,to name a few

have required proofing for hundred of years.

Here are a few links on the subject.

http://www.gunproof.com/

 http://www.bpcr.net/site_docs-results_schedules/documents/pedersoli_proof_rules_and_allowable_limits_09-04.htm

http://www.chuckhawks.com/big_deal_about_proof.htm

http://en.wikipedia.org/wiki/Proof_test

[Victor3]

"All Pedersoli rifles are proof tested at the (Italian government) National Firing Proof House with smokeless powder cartridges with a pressure exceeding that of the ‘commercial’ factory made ammunition by 30 %."

 Notice that Pedersoli tests to +30% (under controlled conditions in a proof house); not some mystery percentage.

 I'll dig out some printed stuff I've got regarding various US manufacturers' proofing procedures during the 1800's. A bit different than the Europeans as I recall. One account of Winchester shotguns I remember tested samples to destruction.

[Double D]

The Proof system in the U.S. is Proof by design and is voluntary.  A new gun manufacurer will (should) proof test the intial design, then proof fire periodically.  The proof is done with a special regulated load design to exceed safe working pressure by a specific ratio.  The Gun that fires the proof load is not released but is maintained in an archive.  A gun Manufacure that I worked with proofed every 100th gun up to 1000, then every 1000th gun there after. Every gun was test fired with standard ammo to detemine if the gun functioned. 

In Europe each gun is proofed using a carefully calculated and controlled load established to develope a predetermined pressure.

What's not said is that in the U.S. the proof system is backed up by tort law.  Under the Europe proof system you do not have civil recourse.

Applying the proof issue to our cannons...what is a proper proof loads...who knows. What should you use as a proof load, who knows.  Standards are not establish for proofing  these guns. 

What is established is the safe building and loading quidelines, these rules of thumb I always preach.   Minumum of one wall thickness around the chamber.  Minumum of 3/8 inch steel in bore liner.  Properly made breech plug.  Determine maximum loads and reduce them "ridiculously".  Use Cannon grade in larger bores.  Don't use lead in larger bores with out a substantial reduction in loads. Always maintain windage, no wads or patches.

The problem of the "double charge of powder and double ball" proof  is you do not know before firing what what pressures are being generated by the load in your gun.  By the way that old proof load, double double was suggested for rifle ands and pistols, not larger bores.

This old mythical proof load has to many variables built into it.   Switlik in his tests found that in equivalant size loads of Cannon grade and FG powder the Fg generated 40% more pressure.  So which powder do you use in the double double cannon proof?

In the old double double proof load they were using friction fit and patched balls.  Are you, can you do that in our larger guns?

The math get way over my head pretty fast, but I comprehend the theory.  I'll let the engineers here argue the numerical aspects with there hoop stregth formulas and bursting strenghs and such.

Bottom line there are no established proofs standards for our guns only build standards.

[BoomLover]

Thank you for that information, everyone. I have wondered how a "safe" load was determined for the cannons, now I know not to overload mine! And a 40% more pressure with Fg over Cannon was a eyeopener, I knew there was a difference, but not that much. The work in finding these load factors probably destroyed many guns in the process, but to a good purpose! Thanks, BoomLover

[dominick]

One account of Winchester shotguns I remember tested samples to destruction.

There is an interesting write up on how a proof test was conducted on the Griffin Ordinance cannon.  They loaded successively larger powder charges with more projectiles until they were able to burst the cannon.  If I remember correctly, it took seven pounds of powder and 13 balls to make the barrel fail.  Now that to me is a proof test.  Don't try it at home!

[Double D]

where is the fine line between proof testing and destructive testing.

[GGaskill]

That final test on the Griffen gun, which was loaded with powder and shot for the entire length of the bore, was intended to burst the gun.  Previous attempts to burst it with lesser loads had been unsuccessful.

[Cat Whisperer]

Proof testing ASSUMES that you have done your design work as a metalurgist or mechanical engineer with EXPERIENCE in gun  barrel manufacturing.

There are VERY few such people that we have access to. 

I will stand firmly on my assertions that I've made on proof testing in the former threads, as having experience as a Tooling Engineer and dealt with mould design involving great pressures, temperatures and much repetitive hammering.

The SAFEST practice that one can do (unless you are qualified as above mentioned) is to follow what the AAA or N-SSA has worked out over the years with MANY MANY people and cannons - use the rules of design set as minimums for guns used in their competition.

Proof testing?  Unless you have run the numbers (based on engineering principles) and employed experience-based rules of design, when you double the charge and place it behind two balls - you are playing with fire. 

As you increase the charge or the weight of the projo, the pressure goes up exponentially! 

Design it right - use the rules of thumb that work!  There are a few of us on this board that have witnessed cannons explode - up close and personal - these are not toys.

[Victor3]

where is the fine line between proof testing and destructive testing.

 Only in labs, I'd say.

 Engineers/scientists create specially designed loads for specific guns built from specific materials.

 They use calibrated pressure/strain gauges, ultrasound, X-ray, magnetic particle, dye penetrant and other non-destructive testing.

 These are reliable tools and processes to detect problems before destructon.

 I aint got none of that stuff in my garage...

[Cannoneer]

There is an interesting write up on how a proof test was conducted on the Griffin Ordinance cannon.  They loaded successively larger powder charges with more projectiles until they were able to burst the cannon.  If I remember correctly, it took seven pounds of powder and 13 balls to make the barrel fail.  Now that to me is a proof test.  Don't try it at home!

where is the fine line between proof testing and destructive testing.

That final test on the Griffen gun, which was loaded with powder and shot for the entire length of the bore, was intended to burst the gun.  Previous attempts to burst it with lesser loads had been unsuccessful.

I don't think that destroying the cannons being proofed was a common practice of the Ordnance Department, it seems like the effort to actually see what a specific cannon could take was reserved for those guns that had exceeded all expectations when they were tested.

Concerning the testing of the "Griffen Gun," the forerunner of the 3-inch ordnance rifle; John Griffen the designer of the gun was present at the tests, and after it had passed the regulation proof firing for iron cannon the gun remained sound, so he was asked if he wanted to continue, and this is when he personally challenged Capt. Alexander Brydie Dyer of the Ordnance Dept. to try and burst the cannon.

The same was basically done to J.A. Dahlgren's designs of his 11-inch and 9-inch shell guns, and Dahlgren himself was also very involved with these trials.

"Design for the 11-inch shell gun was submitted March 24, 1851. By

April 30, Commodore Warrington had approved the building of a model by

Cyrus Alger of the South Boston Foundry. It appears this first gun was

used experimentally for several years and finally burst at the 1959th

round July 18,1855. In addition to shells, the gun had fired 655 solid

shot.

In some respects, the trial 9-inch gun built in 1857 was even more

remarkable. After firing 1,500 rounds of standard 72-pound shell with 10

pounds of powder charge, the gun was successively loaded with shot until

10 shot with a total weight of 903 pounds was reached. With 20 pounds of

charge, the overloaded tube finally burst. The 10 shot had filled the

bore to within 7 3/4 inches of the muzzle."

[Victor3]

 Hmmm... Maybe they shoulda used some of that Dahlgren iron on the Parrotts.

[dan610324]

the scandivavian way to do it in the early 1700 was .

first a careful examination of the barrel , both inside and outside .

then the barrel was mounted in a special designed proof bench that was stuck to the ground that it couldnt recoil when the barrel was fired .

4 shot with 1/4 the ball weight powder + wadding + 1 ball
1 shot with 1/2 the ball weight powder + wadding + 1 ball
1 shot with 1/2 the ball weight powder + 2 balls (no wadding)
1 shot with 2/3 the ball weight powder + 2 balls (no wadding)
1 shot with 1/2 the ball weight powder + wadding + 1 ball

each barrel should be tested in this way before the foundry sent them to the military .
both bronze and iron cannons was tested this way .