How to remove heat scale?

[CoyoteJoe]

I did a bone headed move. In fitting a new Sharon barrel to a Renegade stock I decided to silver solder the underlug in place. That worked great except I took no precaution to protect the bore. The result is that I have a spot of slag in the bore. I can clearly feel it with a tight cleaning patch. Fired patches show a hole on one edge corresponding to a land. I have tried to "lap" out that spot with no luck. As we all know when slag forms on an exterior surface it can be chipped off but is near impossible to sand or file off since it is glass hard. I should have protected the bore with Brownells "heat stop" but just didn't think of it.
Does any one know of a way to remove such slag from inside the bore? :hmm:

 

[ameling]

Scale is just an oxide of iron, just like rust. And a good, cheap, safe way to remove rust is to soak it in household vinegar. So you might want to plug the breech of the barrel, and pour in some vinegar. Let it soak for a couple hours to a day or so. If vinegar works or rust, it should (might) work on scale.

I haven't tried it, but it's worth a shot. And the vinegar won't hurt anything else in your barrel - unless you have some zinc galvanize in it. It will dissolve off the galvinized coating on iron parts. I use it to remove that coating from rivets. Just soak them in vinegar for a day or so.

Hope this helps. Otherwise, you will probably be down to steel wool and sandpaper - which could affect other parts of the bore.

Just some humble thoughts to share.

Mikey

p.s. The other way is to use muriatic acid. But there you are working with some harsh/dangerous chemicals. A friend uses a dilute solution of muriatic acid and water to soak his flint strikers in - to remove that forge scale after he's all done with the forging and heat-treating. It saves him from wire-brushing that scale off. But every now and then he forgets one in the acid bath for a couple days, and that acid "etches" or eats into the steel a little more than he wanted to. He also has to netralize that acid when he takes them out - usually with baking soda and water.

 

[Blizzard of '93]

sure it is actual 'slag' and not 'scale'? if scale then lapping would take care of at least some of it. may have a heat affected zone there is distorted a few thous. maybe try some fine valve grinding compound.

 

[CoyoteJoe]

Well, I don't know whether to call it slag or scale, I just know there is a definite lump of something there. I tried a green 3M pad and a tight patch coated with 220 grit lapping compound. Wore out a bunch of patches and scrubby pads with no noticeable improvement. If it is what I think then it is harder than steel and abrasives have no effect.

 

[44-henry]

Try making a lead lap and using the fine compound on it. You should be able to at least smooth that area up some with this method. Your 3M pads were probably not ridgid enough to deal with that area, the lead lap should be though.

 

[J.D.]

Heat scale comes of pretty easily if it is remove immediately after the part cools. I can be a real bear to remove is it sits 24 hours , or so.

That said, I don't know the best way to remove the scale from a barrel once it hardens. Immediate removal with steel wool or bore brush is the best solution, for future reference.

J.D.

 

[Blizzard of '93]

ditto. keep us posted, may need to try your remedy in future. lead sinker (thru hole for line) makes a good lap when heated, greased and driven into bore. then screw the ball puller into it remove sinker and coat with compound then lap.

 

[Jim-Iowa]

I can't say I have dealt with Heat Scale.
But found a grossly neglected 50 cal CVA barrel in the corner of my garage(ashamed of myself).
I spent a lot of time with a Bronze Brush(12ga).
Polishing it up. By wrapping a patch around the brush saturated with polishing compound it cleaned up very bright and usable. Makes a spring loaded polishing brush.
You might have to use a stronger abrasive as was mentioned?
Another quick tip, cheap bore light is available at the Big Box Store(Walmart) in the sporting goods dept fishing section,look for the Thill lighted bobber replacement lights. Just turn it on and drop it down the barrel.

 

[old gunsmith]

Mild acids like vinegar and muriatic will remove heat scale but you get a very rapid rusting where the fluid meets the air, consequently you really need to submerge the part in the bath to be safe. I think you might have a problem using acid in your bore. I might suggest you try a super penetrating oil called KANO KROIL available from Brownell's and Midway. Kroil is used by many modern benchrest shooters to remove metal fowling because it has the ability to creep under the crud and float it away with little or no cleaning. I believe it will work on your prblem as well. By the way, household ammonia will neutralize mild acids. Regards, Old Gunsmith.

 

[WRussell]

Speaking from zero experience...

If it is slag, not scale, then it's really brittle. If you have access to a lathe, you could make a short rod that just slips down the bore, harden it and grind the end square. It should work as a chipper and remove the slag. Should work on scale too, but of course it will only clear it off of the lands.

A suggestion, if you decide to go this route, is to use 17-4 PH stainless steel for the rod. It doesn't get as hard as carbon steel, but it is easy to harden, doesn't need to be annealed, and most importantly holds its dimensions well through the heat treatment (one hour soak at 900 to 950 F, then slow cool).

If the lump is too big to take out with one tool, you can make one with the first part turned down to a smaller diameter so it will just skim the top off the slag (or scale).

Important to make it a good fit in the bore, so it can't tip and start shaving metal off the barrel itself

What's left ought to come out with a lap without taking too much off the rest of the barrel.

I guess a lap is as good as you're going to get for cleaning it out of the grooves.

 

[CoyoteJoe]

Thanks to all for the suggestions. I have already decided to try the bore fitting hard steel rod idea but it will have to wait now until after elk season which opens tomorrow. I have the truck loaded and will head out in an hour or so.
As is it shoots not too terrible, six inch groups at 100 yards, so I will just try to limp along with it this season and hope for a close shot. It's better than a smoothbore, just not a whole lot better. :grin: