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Double Rifles, Single Shots & Combinations >> Building Double Rifles & Gunsmithing

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Postman
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Reged: 25/09/13
Posts: 846
Loc: Canada

Re: Pitted chambers - a possible solution ? [Re: DarylS]
#330378 - 21/07/19 10:29 PM

I’m thinking the steel epoxy and similar products are maybe the better way. In any event, if it’s pitted, I don’t see how any of these “solutions” would be effective other than for a very short period of time until it crumbles, peels off, etc. I honestly don’t know how one might semi permanently repair the pits without cutting or molten metal being involved. I’m just about the last person to ask when it comes to metallurgy and/or repairs thereof.

Edited by Postman (21/07/19 10:32 PM)

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DarylS
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Re: Pitted chambers - a possible solution ? [Re: Postman]
#330380 - 22/07/19 01:24 AM

I'm concerned with epoxies, there may be some crushing or pulverizing from the pressure of full loads.
I still think the amalgam sounds feasible, or at least the most interesting.
Once set, it is very hard & dense.

--------------------
Daryl

"a gun without hammers is like a Spaniel without ears" King George V

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DoubleD
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Re: Pitted chambers - a possible solution ? [Re: DarylS]
#330392 - 22/07/19 09:32 AM

The old school method is to sleeve the chamber.

The new school method is clean the pits with alcohol apply devcon steel or the MILSURP favorite JB Weld.

Both are frequently used for thAt purpose. Devcon and believe JB also, can be machined when set. After applying ream an polish.

I have pitted .303 Martini chamber to fix this way.

Devcon is amalgam of epoxy and powered steel.

Remember the pressures we talking about are per square inch. The pits are most measurable in.001's of a square inch. As a well a thickness measured in that same miniscule thickness.

What is the actual pressure on say.010 sqin. in a gun developing 18 ton psi.

--------------------
DD, Ret.

Edited by DoubleD (22/07/19 09:34 AM)

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DarylS
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Re: Pitted chambers - a possible solution ? [Re: DoubleD]
#330394 - 22/07/19 01:24 PM

Understand your point.

--------------------
Daryl

"a gun without hammers is like a Spaniel without ears" King George V

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tinker
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Re: Pitted chambers - a possible solution ? [Re: DoubleD]
#330396 - 22/07/19 03:35 PM

Quote:

Devcon is amalgam of epoxy and powered steel.

In that respect, a bowl of cereal is an amalgam.

But I see where you are with the Devcon.
I've used pounds of that material in the industrial setting. I've machined and ground and threaded and textured the stuff many many times on many different kinds of equipment.

It's great stuff. Like anything it has it's strengths and it's weaknesses - and for lighter pitting I can see why a fellow would use it as it has great tooth on most metals. I've used it as bedding on heavy recoiling big bore rifles with great success.

--------------------
--Self-Appointed Colonel, DRSS--

"It IS a dangerous game, and so named for a reason, and you can't play from the keyboard. " --Some Old Texan...

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DarylS
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Re: Pitted chambers - a possible solution ? [Re: tinker]
#330425 - 23/07/19 01:41 AM

Years ago, I used Devcon plastic steel for bedding on all my rifles. After they switched to the 7/1 mix ratio from 50/50, I stopped using it. I had difficulty getting the mix right.

JB Weld works just fine for bedding on lighter recoiling rifles now. Might even work for some pitting problems.

--------------------
Daryl

"a gun without hammers is like a Spaniel without ears" King George V

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Juglansregia
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Re: Pitted chambers - a possible solution ? [Re: theprof1]
#330460 - 23/07/19 04:45 PM

I'd be concerned about the potential for Liquid Metal Embrittlment of the barrel steel.

The susceptibility of various alloys of steel to embrittlement by mercury and other liquid metals is well documented. I'd be researching it real hard before trying it, and consulting with a metallurgist familiar with firearms if in doubt. I've got no idea how mercury when part of an amalgam might affect the chances of embrittlement.

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theprof1
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Re: Pitted chambers - a possible solution ? [Re: Juglansregia]
#330462 - 23/07/19 05:51 PM

Good point, further research still needs to be done, stainless is mercury avid but whether the amount of mercury in amalgam is enough to cause any damage should be looked as various grades of iron alloys react quite differently as i understand.

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Juglansregia
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Re: Pitted chambers - a possible solution ? [Re: theprof1]
#330464 - 23/07/19 07:34 PM

I believe the % of mercury in dental amalgam is around 50%, by mass. Pretty high.

Even copper in the amalgam might be a possible concern, and with a combination of metals present, the influences of pressure etc, Liquid Metal Embrittlement might quickly become a complex issue in this potential application.

Another thing I've seen overlooked in gun work is hydrogen embrittlement from acid de-rusting, plating work etc where the hydrogen is not driven out by appropriate oven cycle. Pretty basic stuff but it requires some understanding of the metallurgy of the part etc. I've seen it overlooked often enough to suggest it here, might save someone some grief.

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Waidmannsheil
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Re: Pitted chambers - a possible solution ? [Re: Juglansregia]
#330465 - 23/07/19 08:13 PM

One question that needs to be asked is how deep are these pits and what size are they? If they are only very shallow and not very big in size then any mixture is going to struggle to take hold for very long. Most of these metal-putty compounds require a reasonable (relative) area and depth to get a good grip. They may hold on initially but I would suggest that after a while will fall out. Undercutting has been mentioned and this would be very helpful and would most likely make the putty stay in regardless of the size of the pit. The problem is doing the undercut. The chamber has a diameter of 0.574" (14.6mm) at the entrance to the chamber which gets smaller towards the mouth and the pits are half way along at 1.5" inches. This would make undercutting extremely difficult and at best you would only be able to access one half of the pit. Undercutting really requires you to be able to access the affected area at right angles so that you can use a very small ball nose or dovetail cutter to remove material.

Micro arc may work as you could bend the electrode into an L shape after grinding the pit to a more open shape. I have had to do this on jobs myself although on much bigger jobs. The restrictive area to work in is going to be the biggest problem.

Matt.

--------------------
There is nothing wrong with vegetarian food, so long as there is meat with it.

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theprof1
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Re: Pitted chambers - a possible solution ? [Re: Waidmannsheil]
#330467 - 23/07/19 08:27 PM

Hydrogen embrittlement is a factor, though more often associated with the involvement of sulphur in the reaction particularly where H2S is involved. The dental amalgam has a range of compositions with copper content in focus, from 0% copper to the higher percentages in standard mixes all giving different strengths and durability. These comments are great as it all works toward a possible easy solution or the discarding of a bad idea.

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tinker
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Re: Pitted chambers - a possible solution ? [Re: theprof1]
#330475 - 23/07/19 11:23 PM

Great points for study!

--------------------
--Self-Appointed Colonel, DRSS--

"It IS a dangerous game, and so named for a reason, and you can't play from the keyboard. " --Some Old Texan...

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Chavez
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Re: Pitted chambers - a possible solution ? [Re: theprof1]
#331610 - 24/08/19 04:15 AM

You might want to try a product called all metal , it’s used in auto body work but I have used it to fill pits in firearms before blueing have to mix in clean metal shavings, it also can be used as a stock bedding , I use car wax as a release agent ,

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tinker
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Re: Pitted chambers - a possible solution ? [Re: Chavez]
#331627 - 24/08/19 11:07 AM

The amalgam idea sounded interesting until we got to the liquid metal embrittlement issue.
I've followed up on the topic and it sounds horrible - just about the worst-case solution for pitted chambers.

The numerous high-tech epoxy and polymer products all have interesting merits. I have a huge textbook in my library, The Handbook of Adhesives and Sealants

https://www.amazon.com/Handbook-Adhesives-Sealants-McGraw-Hill-Handbooks/dp/0071479163

I tend to refer to this book when I look for such solutions

Amalgam sounded great until it didn't.

--------------------
--Self-Appointed Colonel, DRSS--

"It IS a dangerous game, and so named for a reason, and you can't play from the keyboard. " --Some Old Texan...

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