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Joined: Jul 2007
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For a moment I'd like to see the discussion back off Bell and go back to Roster.

At the very least Roster appears guilty of some gross generalizations on a complex subject regarding the 1,500-psi pressure increase. I've no doubt he's fired a load as described that produces pressure spikes as described. But will all loads do this (as he implies)? There is evidence -- not just per Bell but Burrard, G Thomas and maybe even recent CIP proof-house tests -- that suggests this is not the case. Roster should present his evidence in detail and argue from that, also examining contrary evidence (Bell, etc.), before making blanket statements of this sort.

I find similar problems with his argument later in that column about shooting US-made loads in foriegn shotguns -- again, too many generalizations re a complex topic

Metalurgists: what say you to Roster's assertation that pressure increases from long shells in short chambers can result in "cumulative" ... "cracking of the chamber or the bore just forward of the chamber." Assuming, for the sake of argument, there are pressure spikes, does this in fact cause cumulative cracks in areas described?

Lastly, back to Bell: what format of ballistic tests (of the sort Bell does) would satisfy as to being statistically or scientifically valid?

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Jim: thanks for the correction, and I have edited the posted pic.

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Bell is only updating tests that have been done previously. Basically, his tests were a repeat of those the late British gun guru Gough Thomas had done for him by Eley Cartridge. In those tests, 2 3/4" Eley Grand Prix shells were fired in two test barrels. One was chambered 2 1/2", the other 2 3/4". (Bell and ballistician Tom Armbrust used the same barrel, starting with a 2 1/2" chamber and testing a number of loads, then lengthening just the forcing cone, and finally lengthening the chamber to 2 3/4".) Pressure readings were taken at 1" and 6" from the breech face. Pressure and velocity were virtually identical, whether the shells were fired in the 2 1/2" chambered barrel or the 2 3/4" chambered barrel. Note that the Eley shells in question were sold as being safe for use in guns with 2 1/2" chambers--JUST AS TODAY, BRITISH SHELLS FROM COMPANIES SUCH AS GAMEBORE AND MEASURING 67 OR 67.5MM, WHICH WHEN FIRED ARE EVERY BIT AS LONG AS SOME OF OUR AMERICAN 2 3/4" HULLS, ARE LIKEWISE NOTED--RIGHT ON THE BOX--AS BEING SAFE FOR USE IN GUNS WITH 2 1/2" CHAMBERS.

Thomas (who was an engineer by training) concluded, based on the Eley tests: " . . . if advantage is taken of the range of powders with different burning characteristics, nowadays available to cartridge loaders, to design a cartridge for use in chambers shorter than the case length, the extra length of case by itself constitutes no danger."

Roster was correct, in the last part of that column, to point out that American factory ammo most certainly should NOT be used in all foreign guns, even if the chamber is of the appropriate length. But that last section also raises the question of just which guns we need to worry about, because he did not further specify. Is there danger in using an American 2 3/4" shell in a new Beretta or Merkel or AyA with a 2 3/4" chamber? Most of us, I think, would say there is not. But there certainly IS such danger--again, regardless of the length of the factory chamber of the gun in question, and also regardless of whether the gun was made here or abroad--if the SAAMI service pressure of our factory loads exceeds the service pressure for which the gun in question was designed.

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"GregSY, I don't think you are referring to the same Sherman Bell testing that the rest of us are. We are referring to the testing he did on the pressure readings of various lengths of shells in identified chambers. You are apparently referring to his articles on blowing up guns. That is not what is being discussed here. "

I stand corrected - I was referring to his articles on blowing up guns. I still would be interested in know how well calibrated and accurate his test equipment is, but I acknowledge it's far more likely to be valid in that setting. I'll bet the equipment used by the likes of Winchester cost in the multi-thousands range, and for a good reason(s).

Is Sherman's equipment adequately responsive to measure true peak pressures? A lot of the difference between expensive test equipment and cheaper stuff is the ability to consider rise time. In other words, the pressure may peak at a much higher level than he is reading, and drop off, before his device knows it happened. That could explain the difference between his readings and those made by the big guys.

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Greg--You need to read the article in question. It's not "Sherman's equipment", but rather belongs to ballistician Tom Armbrust, who assisted Bell in his various tests. The specific article in question, "Long Shells in Short Chambers", is from Double Gun Journal, Winter 2001. Thomas' report on the Eley tests of long shells in short vs long chambers can be found in "Gough Thomas' Gun Book", pp 260-262, "Danger in Case Length". Note that those tests were done by Eley--like Winchester, an ammunition maker.

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Tom Armbrust did the pressure tests in Bell's stories and Federal contracted his services for pressure testing when they were developing the 3.5-inch 12-g shell. The guy has cred.

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Originally Posted By: GregSY


I'll bet the equipment used by the likes of Winchester cost in the multi-thousands range, and for a good reason(s).

Is Sherman's equipment adequately responsive to measure true peak pressures? A lot of the difference between expensive test equipment and cheaper stuff is the ability to consider rise time. In other words, the pressure may peak at a much higher level than he is reading, and drop off, before his device knows it happened. That could explain the difference between his readings and those made by the big guys.



As noted by GJZ, the equipment used is the same as the 'big guys'. Armbrust uses an industry standard pressure gun. Armbrust is the ballistician used by the 16ga group to test all of their loads. Pressure gathered by Armbrust and reported by Bell can be taken to the bank.


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Originally Posted By: GregSY
[Text Deleted]
Here's the problem with Bell's research. He's using a sample group that is considered statistically insignificant. That's the death knell for any scientific 'fact'. Also, I haven't read his articles in a long time but I don't recall any of his means of measurement as being calibrated.
[Text Deleted]


Ahrgh! Here we go again. How big of a sample size would you want? You've essentially eliminated any scientific argument because you will simply select a "sample size" larger than all the Damascus guns ever produced (or that owners are willing to part with, or that Mr. Bell and others are willing to spend to validate YOUR point)! Yes, you have to take the data with a grain of salt and not treat it as an absolute fact, but that MORE than you can say about what everyone one else says, which is NOTHING, except don't do it. Also, if you had read SOME of his material instead of SKIMMING through it, he clearly states when he uses Tom Armbust's pressure gun to calibrate against and when he doesn't. RTFM please!

The whole Damascus debate is useless to those who close their mind to the materials being used (iron and steel) as being inherently hazardous. Do you know another composite material that is commonly used, abused, taken for granted, and can fail catastrophically killing their owners, yet everyone buys them?!?!? Steel Belted Tires! (A rubber and steel composite, mind you). If you say, "But there's only 35 psi of stress in each tire", please hit yourself over the head with a set of Damascus barrels incessantly until I feel better.....

Mike Doerner - Mechanical Engineer (though I 'spose that's not good enough for this debate, since you'd probably want a Materials Engineer. Grrrr!)

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Jim Legg, My apologies for my 'UP_COCK" this am....wish I had the time to dig out the "Blown Boss Breech" Photo....The unfinished stock that you noted from the photo of the LCSmith was an example that a Gent who had a "Copy Machine" (His term not mine) had built himself.......I gave him the Smith to see what he could do..Not quite good enough for the Trainee stockmakers That I was Guiding for the Veterans Administration Program for Disabled Combat 'Vets",Both WW2 (one) Viet Nam (Four)I had Double Amputees, and I was always looking for ways to take some of the "Grunt-Work" out of "My Trade" to help them master the ReStocking & ReForending of both shotguns & rifles.(This was done in 1984!)The Blown Breech Pic'was "HI-Lighted" to emphasize to the "Young,Upcoming Shotgun Shooters that I was guiding on the Trap&Skeet Fields....Do Not Under Any Circumstances use Somebody Else's Reloads....cc/dt

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I'm still waiting to find out what "the other board" Salopian referred to, is. I'd like to read what others are saying about this month's column.
Thanks


> Jim Legg <

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