16ga.com ~ View topic - Requesting Wisdom Regarding Questionable Chamber Integrity

Joined: 22 Jan 2015 Posts: 345

Yes I plan to have a pro inspect the gun’s chamber....However, I have descerned a great deal of competence here from many regarding advise and perspectives I hadn’t considered otherwise. Therefore I’m fielding a question for which I’d appreciate some feedback that I can add to my understanding of what I’m seeing and suspecting in order to be better prepared for my visit to my gunsmith.
I have a nice 16ga double which I can make out with a good light, what appears to be a semi-circle of pitting in the chamber about 2.5-2.75” in from breech, and well before forcing cone begins to taper. Originally when I spotted it, I miss took it for wad or plastic fouling. When much scrubbing made no change, I realized something was amiss, and using a dental pick, was able to verify that what I was seeing was a depression not standing debris. Not very deep, and not continuous, but around the chamber like a ring. If I were to guess, I’d say it’s likely the result of improper cleaning before I acquired the gun, and comes from corrosion.
I realize that this is potentially dangerous if ignored, but I’m not sure where the line ought be drawn to say it’s now a wall hanger. Would that be a simple matter of wall thickness of chamber? Thanks for any in depth knowledge someone might offer to consider. I can post a pic of what I’m seeing later, but it’s not borescope close up.

A side note: I know when the gun first came to me, that this wasn’t evident. That’s why I originally suspected fouling. But I hadn’t had the gun but a week or so before I first shot it, and as is my routine, I promptly cleaned and inspected it, so I know this is not from any neglect I might have done. Therefore I’m puzzled why I didn’t spot this pitting initially. I wonder if maybe some character used a dishonest technique of leading to fill in and cover up that pitting, and was latter shot out???

Joined: 22 Feb 2019 Posts: 63 Location: United States

that type of scar is caused by an unfired cartridge being left in the gun for a long time.if you shoot ammo that uses plastic wadding I would leave it alone removing any metal from that area of the chamber will not make it any stronger. The little ring of roughness will have no affect on guns performance.

Superficial pitting at the end of the chamber is quite common

This is looking toward the breech

Only an experienced barrel smith with a bore scope can provide an assessment.

End of chamber wall thickness is the critical measurement.

Joined: 22 Jan 2015 Posts: 345

The last pic above looks very similar to what I’m seeing.

Member Joined: 09 Jan 2013 Posts: 2168 Location: Florida

"End of chamber wall thickness is the critical measurement."

Joined: 24 Jul 2016 Posts: 548 Location: Ohio

Drew, do you shoot that gun?

Min wall thickness at end of chamber should be 0.090 thick, most would prefer more, a couple might gamble on less, but it is a gamble.

As to your question on whether someone hid the defect, It cannot be known for sure, but my gut it is more likely than not they did not see it as dirt and crude can fill and hid pits, even after you have run some patches through the gun. I never ceased to be amazed how many used guns I look at have dirty to filthy barrels. Few people do the repeated cleanings over several days to make their old rough barrels immaculate. The rougher the barrels the more likely some packed in crude is hiding something and will take some cleaning.

At the end of the season or when I will be parking a gun for a week or more, it gets cleaned really well, then again the next day, then again on a third day. On some guns I drench the bore with ed’s Red after it overnighted with eesox’d bores in the morning and come back in the evening the run more ed’s Red and patches till clean. Yes I am obsessive, but cleaning to perfection requires work, and can reveal things you missed when not immaculate.

Joined: 16 Jul 2015 Posts: 2124 Location: Hudson,Wy

The figures I have show .090" as minimum at the breech and .079" minimum safe wall thickness at the end of the chamber. This is listed for so called "standard" fluid steel.

Whitworth and a number of other steel specifications do have different minimum wall thickness standards, with some of the very best requiring slightly less wall thickness and Damascus or twist steel requiring greater wall thickness.

The weakest point will of course be where the deepest pit lies at the end of the chamber. How to measure the deepest pit? Well there is the expensive option of metal analysis like Doc Drew just went through and he would be able to give far better advice along that route than I. There is also the option of honing until the last pit is gone since the deepest pit is already the thinnest/ weakest point, then measuring wall thickness. If it passes you have a useful gun. If it is too thin, then you never really had one to begin with.

Joined: 22 Jan 2015 Posts: 345

Option to “hone the chamber”? That brings a new question to mind. What kind of tolerances are generally called for with regard to chamber internal diameter dimensions? I would be surprised if much slop is ok.

Joined: 16 Jul 2015 Posts: 2124 Location: Hudson,Wy

Therein lies the problem. If the pits are deep enough that the chamber ends up sloppy, then that won't work out. Bores are a different story, as long as sufficient thickness remains, there is a wide range of tolerance. At this point, I would find and experienced shotgun barrel smith and see what he thinks. A qualified individual may be able to just look at it with a bore scope and pass verdict.

WyoChukar,

You are correct as usual and the thickness will vary from gun maker to gun maker. A German Gun with Krupp barrels will probably be different than most American made guns. The quality of the barrels will have a lot to due with the min thickness requirements.

Pine Creek/Dave
L.C. Smith Man

Joined: 04 Mar 2019 Posts: 1837 Location: Central ND

I think that you will find that pitting or other sharp edges in/on any metal that is subjected to stress is where a failure is MOST likely to start. Sharp edges have the nasty habit of being an area where metal begins to fail as they create stress risers.

Working for Pratt & Whitney, all sharp edges were/are broken either during machining or afterwards by deburring.

During a welding operation any undercut left by the welding process usually needs to be smoothed by grinding. A little bit of thinning the base metal does not compromise the component as much as the sharp edge of the undercut will.

My point is while wall thickness of a chamber or bore is something to be mindful of, the pitting and sharp edged ridges will cause a failure quicker than a wall thickness being too thin by a few thousandths of an inch.

MSM2019,

What you say is absolutely correct, good to see a P&W guy here on the 16 board. We may know each other, I worked for HSD and advised P&W on may Welding Engineering projects the last 10 years of my Welding Engineering career. Came in from NASA to help with the Aero-Space Welding Engineering because of some of the more technical problems.

Retired about 10 years ago, hope all is well at United Technologies P&W! Good professional advise by the way.

Pine Creek/Dave
L.C. Smith Man

*Last edited by revdocdrew on Thu Jun 13, 2019 2:57 pm; edited 1 time in total*

Mark's point is well made. Only a good smith with a bore scope can ID linear erosions (an impeding crack?) like this, while the barrels have adequate measured wall thickness

Joined: 04 Mar 2019 Posts: 1837 Location: Central ND

Pinecreek/Dave,

Unfortunately or fortunately, I worked for P & W from 1979 until 1992. I needed 15 years of service to make it through the layoffs/downsizing at the CT plants. I had 13 years.

Anyway, it was a great company and I learned stuff there that has carried me through.... I will be retiring from my current position as an Apprentice Training Coordinator in 21 days-15 Hours-32 Minutes -8 Seconds.