Unknown Belgian Maker (barrels possibly by Gilles Heuse, Nessonvaux) c. 1898-1910 "Cast Steel" - by METL's composition analysis very low carbon AISI 1002 with a measured tensile strength of 54,500 psi (similar to pattern welded barrels). Both bores with marked pitting.



Chambers lengthened by Briley Manufacturing 3-2019; requested Left 2 3/4", Right 3".
Briley BTW does not afford an "in the interest of science" discount

…………………………..LEFT………………………….…RIGHT

……….…..………Before……….After……….…..Before…………After

Chamber…………2 5/8”…….….2 13/16”………..2 5/8”……………3”

Bore………………0.723”………………………...... 0.725”
………(Marked 18.2 so possibly previously honed; 18.4 mm = .724”)

…………………………………WALL THICKNESS……………………………

End of chamber
……….Top……….0.100”……….0.090”………….0.105”……….0.086”@2 7/8”
…………………………………………………………………0.090”@3”
……….Side………0.110”……….0.110”………….0.122”………..0.102”@2 7/8”
…………………………………………………………………0.110”@3”
Start of forcing cone (estimated about 1/2” in length before chamber lengthening)
……….Top……….0.127”……….0.100”………….0.120”……….0.108”
……….Side………0.132”……….0.115”………….0.147”……….0.120”
3 1/2”
…….....Side………0.114”………………………….0.133”
4”
……….Top……….0.110”…………………….…….0.104”
……….Side………0.104”………………….……….0.125”
9”
……….Top……….0.072”………………….……….0.084”
……….Side………0.080”………………….……….0.084”


Summary of measured end of chamber wall thickness:
http://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=379803&page=3

Summary of recommended wall thickness:
https://docs.google.com/document/d/1ZIo0y746UsSRZIgRuuxwAbZjSBHitO_EanvwLYc-kGA/edit

Impression
I was previously mistaken and now surprised by the loss of wall thickness lengthening one chamber only 3/16"

Lengthening a 2 5/8" chamber to slightly longer than 2 3/4" resulted in a (new) end of chamber wall thickness of about 10% less. There was also a significant loss of WT at the start of the forcing cone, but the resultant WT was still greater than the end of chamber WT.

Lengthening a 2 5/8" chamber to 3" removed about .020" of end of chamber WT, resulting in a below recommended WT.

I would NOT lengthen any vintage double chamber with end of chamber WT less than 0.110".

load with heavy black powder shells...tie gun to tire...tie loop in lanyards and attach to triggers...step behind tree, or wall...cross fingers an let her rip for both barrels...observe results...repeat twist...

So said Drew > I would NOT lengthen any vintage double chamber with end of chamber WT less than 0.110�.

One data point with an ancient and obscure barrel doesn't mean much.

And you took your MechE graduate degree where?

Actually Dogfox, I only impersonate a metallurgist here on DoubleGun.
I have however spent a lot of personal $s and time studying and discussing vintage gun barrel steels with the engineers at METL. It is quite likely that the "Cast Steel" barrel is Decarbonized steel, but I will know for sure when I have it zapped along with the vintage double frames for composition analysis. Those of us choosing to use ancient and obscure guns might be interested
https://docs.google.com/document/d/1dnRLZgcuHfx7uFOHvHCUGnGFiLiset-DTTEK8OtPYVA/edit
I've also researched wall thickness recommendations (see the links above) and have discussed such with gunsmiths. I should have made clear that my recommendation was for vintage doublegun barrel steels.
I'm simply offering an opinion, and interested in opinions of others, including yourself. Please share yours, and the basis for that opinion.

Thanks, Drew, for your information. While it is but one gun it does offer a good illustration of the potential effect and consequence of lengthening chambers. Keep up the good work�no one else is stepping to the plate with firm data. If nothing else data like this should cause those contemplating such changes to hesitate and reconsider.

Dr. Drew do you have the action to try a test to destruction ? I am absolutely not advocating lengthening chamber, but I bet it would pass proof. We all need as much "meat" as possible in barrels, as accidents happen. Sherman Bell's previous tests seem to indicate the old ones are tougher than some people give them credit for. But human nature what it is, people can even blow up new steel barrels. ymmv

Mark: I am going to ask METL to tensile test a segment of the "Cast Steel". If it turns out to be Decarbonized steel, it should be noted that Meriden and Crescent "Armory Steel" and "Parker Steel" were each shown to be Rephosphorized Decarbonized steel by composition analysis; "Remington Steel" on the Hammerless Model of 1900 was reported by Remington to be Decarbonized steel also.

Several testing labs in the U.S. do formal proof testing - but the cost starts at about $500 per test.

A mechanical engineer friend in Vegas, who has been active on the PGCA Forum, was investigating using a hydraulic pressure failure test, and has some of the pattern welded tubes I used for the tensile testing published back in 2014. Marriage, and a job have gotten in the way, but we'll see.

My thoughts??? Exactly the same thoughts I had in the previous thread on this subject, which was unfortunately deleted.

It was clearly evident then, that chamber lengthening in virtually all vintage double shotguns would result in LESS wall thickness at the end of the new chamber. Nothing has changed. Miller graciously provided his drawing with notations added to illustrate that, which you continued to reject and deny.

You also rejected the simple explanation I gave for why chamber lengthening in these guns would absolutely result in LESS wall thickness at the end of the new, longer chamber. You questioned what Miller and I saw so clearly and easily, and demanded to see actual measurements of wall thickness of chambers I personally had lengthened. The most expensive measuring tools in the world are useless when you can't grasp simple ideas and 8th grade geometry.

To me, that was just silly, and it was proof that you are not qualified to pretend to be any kind of shotgun barrel expert. It was like demanding that I provide measurements and proof that shortening barrels actually makes them shorter. I am just amazed that you went to all this trouble to confirm what is so clear and self-evident. Paying Briley to cut a chamber deeper to confirm it simply proves the old adage: "A fool and his money are soon parted."

It all depends upon the barrel thickness you begin with. Whatever metal you cut out to lengthen an existing chamber will reduce the remaining chamber thickness. Some barrels though are thick enough to extend the chamber and still be well within safety requirements.

For example, in an earlier thread I mentioned an ithaca/lefever single shot 20ga I have that had the chamber extended from 2 3/4" to 3". Most American single shots are built pretty stout. The gun I have is particularly thick from the breach to the end of the action, well over three inches long. I had mine measured as a precaution and the extended chamber walls extending well into the forcing cone are at the thinnest .130" thick. I will open the turkey season in the morning with it.

SXS guns are built for weight distribution and handling comfort, so even American doubles are more likely to have a barrel thickness problem in the chamber area than single shots. But, some are certainly built strong enough to be OK with a chamber extension. I'd venture that most "duck" guns will stand a chamber extension whereas many "bird" guns simply won't. Measure twice ream once...Geo

over the years, i have axed old ed, my go to gunsmith, to lengthen chambers on a variety of 2 1/2" double guns...first thing old ed would do is to measure barrel wall thickness in front of the chambers...never had him declare "too thin" for an american made gun...occasionally, he would refuse to do work, on light weight european made guns, because barrels walls were "too thin"...16 gauge frenchie gons come to mind...

I believe I had put up two pictures on that thread prior to it being deleted. Looked through my files & I know one of these was what I used, but not positive about the second one. Anyway here goes;
This first one is of the unmodified chamber.



2nd pic is of a lengthened chamber with the blacked in portions being the metal removed in the process. Upper side shows a 5� per side angle to the cone. Lower side shows the cone cut parallel with the outer wall. On this particular drawing that gave a cone length of approximately 1�". This would, of course, vary on individual guns.


Normal taper for the chamber itself is about 005" per inch. The barrel's OD will universally have a steeper taper than this in the chamber area so any lengthening of the chamber will result in a thinner wall at the junction of the chamber with the cone. Whether or not this creates a dangerous situation depends totally on both the barrel steel & its dimensions.

It is as patently Wrong to say that all chambers can be safely lengthened as it is to Say that None can be. It simply has to be determined by a knowledgeable person on an individual basis.

PS; You can click on the thumbnail pics & enlarge them for easier viewing.

Thank you Miller.

This is a No. 0 "Good 2 Iron" 16g Smith with chambers lengthened to 2 7/8" with end of chamber WT of .102" right and .105" left, that still bulged; with what load is unknown



X-ray of bulge




Part of my confusion was related to my 1906 12g Armor Steel Smith that I discovered to have chambers of 3 1/4" after forcing cone lengthening. The end of chamber WT was still .118" right and .112" left. Clearly the pre-lengthening WT was substantial.

Looked some more in my records and found a Parker 12g Grade 3 2 frame with D4 barrels with chambers extended from 2 5/8" to very slightly more than 2 3/4" - end of chamber WT .100" right and .114" left.


As said over and over, lengthening British 2 1/2" game gun and U.S. maker's small bore chambers should be done only by a barrel expert and with great caution.

It might be interesting to measure the barrels of some 20-gauge Browning Superposeds from the days when they were only made for 2 3/4 inch shells and after they began chambering the hunting models for 3-inch shells.

I. Have not read the whole thread as I am on a very small computer at the moment, but is it proper to consider that the pressure at 2 3/4� is less than at 2 1/2� in a normal shell ? If so the calculation of the safe stress at each distance should be made, and that seems to say the wall thickness at the 2 3/4� distance could be thinner than at the 2 1/2� and be equally as safe in each area.

Ancient pressure-distance curves





Modern, but computer generated



Clearly modern fast powder have a higher 1" pressure which then falls more rapidly than old Bulk or "progressive burning" powders, even with the same total area under the curve

A pressure curve that shows higher pressure at the point of the standing breech than at the point in the chamber where the powder charge is situated in the shell should be viewed with extreme skepticism. After all, it is the rapid burning of the powder, which sits between the base wad and the under shot wad, which generates the pressure. Peak pressure will obviously be generated very near that point. We don't see examples of early pressure test barrels with lead crushers at each and every point along the full length. So it should be obvious that there was considerable interpolation and conjecture involved in the early pressure curves. And we would also have to assume that even the modern computer generated version relies on some unknown technology that would provide continuous pressure data at every point as the charge passes down a 30" barrel. We would similarly need to have piezoelectric transducers installed along every point of the barrel to know precisely where the shot charge was at a given time in the pressure curve. Multiple strain gauges could be installed along the full length of a barrel, but they are not as accurate as piezoelectric transducers which require a hole in the chamber wall. As it stands, we rely on the ideal gas law to know approximately where the shot charge is at a given point in time. But the pressure is variable, dependent upon the burning rate of the powder in a confined space of continuously variable volume.

well yeah keet, what you state above is obvious...but you forgot to factor in the phase of the moon...

Historically, "breech pressure" using crushers (LUP) was measured at 1", as are the piezo transducer SAAMI and CIP standards today

I really learn a lot here. Checked Amazon for that Bernard dehydrated water, but it must be out of stock or discontinued. Sure would make those deep forays into the Sandhills easier without that water bottle banging against my back in the game bag.

Mike

Yeah, but you have to reconstitute the stuff with goat's bile

Since I've always learned best with pictures I cut the left barrel.
The chamber was lengthened from 2 5/8" to 2 13/16". End of chamber WT at top 0.100" before to 0.090" after; start of forcing cone 0.127" to 0.100". At 4" top is .110"

Sawed the 16g SAC barrel that was the victim of inexpert forcing cone lengthening and honing.



The chamber was still 2 9/16" but the wall thickness at the end of the chamber was .087" and at the forcing cone .098".

The pilot put dents in the barrel, and long furrows in the bore; looking toward the breech



Barrel transected




Radiograph



The forward straight lucency is where the thinner tube was butt welded to the thicker breech section

People need to buy a Mec 600 jr, cut a few shells down and load proper length shells with reasonable pressures. This butchery, to shoot too long and way too high pressure loads in a gun is insane. You can still reload 12�s for less than you can buy factory shells for most of the time. And factory shells are 10-11K psi so they can work an 1100, which is 2K more than most doubles were built to handle.

so then, what conclusion can one draw from this thread?

besides stan is a jerk...

and brent is child like...

Never ever buy a gun from you if it has lengthened chambers. Never.

Different ones of us may draw slightly different conclusions, but you will draw none. That's because you always want others to do the thinking, and the leg work, for you. You do nothing in the way of research for yourself.

gee stan, happy new year to you too...

In one photo showing the breech scoring, isn't there a clear crack at about 12:00?
Tom Bryant, late of Cabelas, gave me a tip. Use your cell phone camera to snap a shot, then expand it to see stuff better.
It really works.

Joe

Is this the image Joe? There could well be several cracks. They were not apparent on the radiograph, and if not deep, mag particle inspection would be unlikely to show them either.
I think whatever is at the top is from the cleaning material

Top one sure looks like a hair or a thread to me.

I think that crack is an artifact. It loops back onto itself if you follow it upwards. Could be a fiber. But the overall point to me still is why do many of the alterations that we do to guns. I no longer recolor guns. I no longer alter chambers, I just load shells that fit and are the safe pressures. But to be fair I have too many guns so it a gun is "marginal" for use I just do not use it anymore. It is a judgement call and people need to figure out their comfort level and do as they deem fit. The too short chamber, anti Damascus police, have no room in my life.