doublegunshop.com - home Forums Thread Like Summary - 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".

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.

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.

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.

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