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#546106 - 05/16/19 01:29 PM "The Southern" Chamber Burst
Drew Hause Offline
Sidelock
***

Registered: 01/18/06
Posts: 7517
Loc: AZ but dreaming of KS
Will try again and start the summary thread here as the format on the LCSCA Forum makes it hard to follow long threads with multiple replies.

Many thanks to all those involved, and especially the gun owner, with whom I have spoken and who graciously allowed this evaluation. I freely admit that my initial assessment was wrong; there is no obstructional ring bulge, and the gun was not the victim of inexpert chamber/cone lengthening.

I claim no metallurgical or engineering expertise. My information comes from conversations with the metallurgical engineers at METL and several gunsmiths in preparation for “A Blow-Up Post-Mortem”, published in The Double Gun & Single Shot Journal, Vol. 27, Issue 3, p. 17, 2016
and summarized here
https://docs.google.com/document/d/1ZnptAPvQIlWG5n5UU2FmKcFpYtVmOSc4b7K7G9IBs4g/edit

It doesn't take a lot of brains or talent to record wall thickness numbers; just the equipment and practice therewith to establish repeatable numbers and the willingness to spend the time to do it right; and it does take time.

The gun is a 1908 Regular frame 16g No. 00 L.C. Smith with fluid steel barrels; though without the usual “Armor Steel” barrel mark; it does have a faint 'C' we believe for Crucible Steel but no SB&Co.

The shells were Cheddite for Herters “Select Field Dove and Quail” 1 oz. at 1165 fps, or the old 2 1/2 Dr. Eq. I have no pressure data for that load, but similar loads run about 9,000 psi. The hang tag that came on that gun listed 2 1/2 dram 1 oz. shot, and Nitro powder loads then had similar pressures as today.

The gun has been used regularly since purchased 2 years ago. The owner states that the chambers have been measured at 2 3/4”.

The burst occurred at the 2019 “Southern” on the Sporting Clays course. The shooter did not perceive anything out-of-the-ordinary before or with the burst; other than the loud report. No increased recoil. A piece/pieces of barrel struck the tree to the right but was not recovered. The shot through the barrel immediately before the burst was normal; no FTF or soft report.

Images courtesy of Cheryl Stubbendieck





Note that the rib has been lifted

Thoughts from Dewey Vicknair



Hunter Arms used a brazed hook and rib extension; courtesy of David Elliott



and the wall adjacent to the wedge hook piece and top rib extension piece are flat

12 gauge



The subject 16g gun






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#546107 - 05/16/19 01:33 PM Re: "The Southern" Chamber Burst [Re: Drew Hause]
Drew Hause Offline
Sidelock
***

Registered: 01/18/06
Posts: 7517
Loc: AZ but dreaming of KS
It has been proposed that the failure initiation point was the dark divot shown here, with failure of the braze joint + the now unsupported thin wall +/- a flaw (?inclusion) at that point; with the gasses being vented superiorly



After wiping with Shooter’s Choice, without use of an abrasive



Courtesy of Dewey Vicknair



The shell used in the burst chamber. Clearly the Cheddite hulls have a separate plastic base wad, part of which is missing. The brass base has fractured and a section of the hull is also missing.



Examination of the 7 empty shells used immediately prior to the burst (saved for reloading) shows the base wads are in place and complete, and each has a factory primer. 8 unfired factory shells have the same primer.

The burst shell IS A RELOAD with what is likely a Cheddite Clerinox 209 primer. The primer has been displaced out of the pocket, is bulging outward, and the (partial) base of the shell has a distinct extractor indentation.

Clerinox primer, burst shell, factory Cheddite/Herters right



Fractured and flattened rim



Extractor imprint



Major Sir Gerald Burrard The Modern Shotgun, Volume 3, The Gun and The Cartridge, “The Diagnosis of a Burst”, 1948
identified an indentation of the extractor on the case head, enlargement of the case head, flattening or fracture of the rim, lifting of the primer from the pocket, flattening of the primer against the breech face, and deep striker indentation, especially in comparison to shells of the same batch, as evidence of excessive pressure.

Ballistic testing of the unfired factory shells, while of interest, is not relevant.
FYI:
Downrange Mfr. only tests 12g shells
Precision Reloading will not test factory shells; information regarding shipping (NOT by USPS) is here
https://www.precisionreloading.com/docs/uploads/BALLISTIC%20TESTING%20INFORMATION-2.pdf
Tom Armbrust will test 16g loads
1108 W. May Ave, McHenry, IL 60051
Note new (cell) phone: 815-451-6649


Measurements

The left chamber is 2 9/16” measuring .750” at the breech to .738” at the end of the chamber. Superficial tools marks are present in both chambers.
The left forcing cone is 9/16”; right could not be measured but visually appears the same.
Both bores at 9” are .650”.

A 1907 Hunter Arms engineering drawing specifies 16g chambers as .745” tapering to .732” with a 1/2" forcing cone to a bore of .650”.

Impression: Slight disparity in numbers likely insignificant. No evidence of modification to chamber or bore.

Wall thickness

End of the chamber L .096”; R could be measured and .105”
Forcing cone L .112”; R .126”
9” from breech L .046”; R .042”
9” from muzzle L and R .032”
MWT was several inches in mid barrel and both .028”

Impression: adequate wall thickness

SUMMARY

1. There is no evidence of chamber, cone, or bore modification; and wall thicknesses are compatible with other measured 16g Regular frame Smith guns.
2. The burst shell was a reload, and shows evidence of over-pressure.
3. There is visual evidence of failure of the braze joint, and a suggestion of a defect in the barrel wall which served as the failure initiation point.

Unanswered questions:

Would the chamber have burst without the over-pressure shell?

Is the top rib extension wedge brazed to the thin medial barrel wall a design defect, or was this a manufacturing error?

Did the use of 2 3/4" shells in a 2 9/16" chamber add to the over-pressure? The once fired Cheddite hulls are a full 2 3/4". Sherman Bell's study of 2 3/4" shells in 2 1/2" chambers showed a rise in pressure from 228 psi to 1216 psi compared to 2 3/4" chamber with a 1" forcing cone.


I plan on asking an engineer at METL for an opinion regarding the failure of the braze joint.



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#546108 - 05/16/19 01:40 PM Re: "The Southern" Chamber Burst [Re: Drew Hause]
Mark II Offline
Sidelock

Registered: 12/06/11
Posts: 610
Thank you for all your efforts!

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#546109 - 05/16/19 01:59 PM Re: "The Southern" Chamber Burst [Re: Drew Hause]
Dan S. W. Online   content
Sidelock

Registered: 08/17/13
Posts: 414
Loc: Atlanta, GA
Interesting the way the shell splits when fired without a chamber altogether. Very similar to the above. Almost like the barrel wall provided no resistance whatsoever:

https://www.youtube.com/watch?v=_SSdLQcGEio


Edited by Dan S. W. (05/16/19 04:15 PM)

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#546110 - 05/16/19 03:18 PM Re: "The Southern" Chamber Burst [Re: Drew Hause]
KY Jon Offline
Sidelock
**

Registered: 03/09/02
Posts: 6265
Loc: Red State
Was it known that the shell was a reload the entire time? Looking at the obvious signs of over pressure, the way the primer flowed into the area around the firing pin is classical, the way the hull rim expanded into the extractor area is the same.

Are we certain this is a reloaded shell? One problem I have with low pressure reloads is that they often don’t take up enough room in the hull. So if extra anything gets in the hull, that extra space just gets filled in and the crimped shell can look normal. People think all over pressure loads are double charges of powder but they do not have to be that much extra powder. Makes you think of how lucky we are in our reloads. I’ve loaded several hundred thousand shells with no graphic failures like this one. Worst for me is the odd cocked wad or squibs loads

I had a PW machine which would create an overload problem in 20 gauge. Talking with one of the fellows at Alliant I was told using Green Dot, my all purpose powder at the time, four to five grains extra powder would cause pressures to climb quickly in dangerous ranges. I sent that machine back twice to PW who went over it. It still had the same problem so over the side of a bridge it went.

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#546113 - 05/16/19 03:43 PM Re: "The Southern" Chamber Burst [Re: Drew Hause]
Joe Wood Offline
Sidelock
**

Registered: 12/31/01
Posts: 3483
Loc: Texas
i agree, Ky Jon, the blown hull exhibits excessive pressure and I think we will find it was the catalyst for the blowout though the barrel vas weakened by poor joining and evidently a crack that went undiscovered for a long time.
_________________________
It ain't whether you hit a bird that matters, it's the fun you have even if you don't.

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#546118 - 05/16/19 05:13 PM Re: "The Southern" Chamber Burst [Re: Drew Hause]
Mills Offline
Sidelock

Registered: 01/10/12
Posts: 214
Loc: GA/SC
Very interesting. Thanks for your work Drew! We can use all the knowledge we can get

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#546121 - 05/16/19 06:16 PM Re: "The Southern" Chamber Burst [Re: Drew Hause]
gil russell Offline
Sidelock
**

Registered: 02/27/03
Posts: 1354
Loc: Southwest
Very interesting; thank you for sharing that. Gil
_________________________

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#546126 - 05/16/19 06:41 PM Re: "The Southern" Chamber Burst [Re: Drew Hause]
Geo. Newbern Offline
Sidelock
***

Registered: 01/02/02
Posts: 6699
Loc: Georgia, USA
Maybe third thread will be the charm, Dr. Drew. Thank you for sharing your investigation with the rest of us...Geo

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#546131 - 05/16/19 07:23 PM Re: "The Southern" Chamber Burst [Re: Drew Hause]
JHJ Offline
Sidelock
*

Registered: 01/01/02
Posts: 232
Loc: Central SC
In as much as the word "detonation" has been disqualified, I'll gladly settle for "burst".

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