doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Help needed on pressures of modern loads?

In July 2006 I contacted Roger Hancox, Proof Master at Birmingham and asked for a comparison of 850 bar and 3 1/4 tons per square inch. The reply I received was detailed but beyond my comprehension. Perhaps someone with an advanced degree in maths and/or engineering could come with a practical comparison chart, so that so that we ordinary people can be confident That we are selecting shells that develope pressures suitable for safe use in our English guns. Mr, Hancox E mail address is ACVOKE@aol.com.

PS. Here are the conversion factors that apply:
1UK. long ton =2240 pounds. 3 1/4 tons per square inch =7280
1 Bar =14.50377 p.s.i.

As you may have already guessed a strict mathematical comparisons is not applicable.

I emailed the Birmingham proof house some time back and asked what loads should be used in a steel barrelled hammergun with NITRO 1 1/8 proof marks from between 1904-25.

They replied:

"Dear Writer,
I am not sure where you are but guess you are sited in the U.S.A. so I will answer both ways namely:-
a. U.S.A. answer it can be used with standard velocity 2 1/2" nitro cartridges where the shot load does not exceed 1 1/8ozs and the packets made in the U.S.A. will be marked 2 1/2 dram equivalent.Must be lead shot.
b. G.B. 850 bar marks on box for 2 1/2" 65mm nitro cartridges standard velocity -1 1/8oz load of standard lead shot."

GDU

2240 x 3¼ TSI = 7280 PSI
7280 PSI ÷ 14.50377 = 501.938 BAR
These are the simple mthamatical conversions. What has to be understood is this is applicable only as long as we are talking the same system. Thus 3¼ Tons (Crusher) is equal to 502BAR (Crusher) or 7280 PSI (Crusher). It is not equal to 502 "Actual Bar" nor is it equal to 7,280 "Actual PSI". The actuals in both cases would be higher. The "Tranducer" pressures for 3¼ tons should be about 9800PSI or 675 Bar.

I just emailed the proofhouse and asked them the same questions as Roy and Greg. Still awaiting a response. In the meantime, I'm confident that Miller's figures are within the safe range for guns carrying the old "tons" marking.

Rev,
Given all the cautions about American ammo mfrs ammo that "must be assumed to be maximum SAAMI pressure because lots of powder drive pressure all over the place and only velocity is maintained", and the confusion with conversion from one system (LUP/psi), the Armbrust finding of a error or misunderstanding, and the fact that some of these mfrs don't publish pressure data but 'responded' with data, and lastly the small but precious fingers and eyes that you have grown attached to, ....wouldn't it be prudent to get independent pressure data, rather than trust an email?

Over the years, the reloaders on this bbs, for various age guns, have exercised conservatism in selecting loads by dropping pressures below what they believed the subject gun was proofed/built to handle. For an older gun, I think its equally wise to do the same with factory loads, especially given the confusion over conversions between LUP/piezio psi.

Arbrust's services or a Pressure Trace will look very cheap after a serious problem.

Just my thoughts on all the discussion in this very informative thread.

Certainly reasonable Chuck, and the 16g Low Pressure Reloading Group has done that, with both factory shells and reloads
http://www.16ga.com/forum/viewtopic.php?t=921
And if engineers, research scientists, and physicians the world over have agreed to speak the same 'language', why can't the British, French, Italians, Germans, and Americans...oh...never mind

C'mon Doc, half the time engineers and schientists (yeah, i spelled it that way on purpose) can't communicate across a room, let alone with physicians. That's how they muffed the Mars approach wadent it?

Stay safe, Doc

I think Miller summed up the situation concisely.

Take a look at the second picture, "appareil-manometre a multiples crushers", "pressure test apparatus for multiple crushers". A very slick piece of test equipment in the 19th century!

The more I look at that piece of test equipment, the more the phrase, "human error" goes through my head. I am sure that on the best of days, every effort was made to achieve the highest degree of human precision to measure those crushers. I also wonder just how far off the measurements could have been on the worst of days. Besides just the measurements, some pretty slick statistical techniques would have to have been in use to throw out the aberrations that human error potentially introduces. All of this gets put by the wayside with the introduction of transducers.

Why certain groups insist on using outdated terminology is a mystery to me. The sensor and circuitry are wired to show the output using a chosen nomenclature. However, the raw data is independent of this gibberish. In other words the sensor is producing either voltage or resistance. Call it that.

Pete

Sometimes, I don't think we give enough credit to the capabilities of our forefathers from the 19th century. It's test devices like that rifle that were the basis for the tapers rifle barrels have.

While a tranducer certainly has some advantages, the need for statistically significant samples still holds true.

As for giving transducer raw data in voltage or whatever, it would seem to me to be useless unless one knew what the comparative calibration of voltage/pressure was.

Sometimes a significant sample can be very painfull. Much of it is common sense which is probably why many old Damascus barrels hold up well. They were overbuilt for safety.