doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Chamber Lengthening Wall Thickness Trial

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...