I have my Winchester model 12 in the shop that has been with the family since it was bought a long time ago. The gun locks up during firing and it can't be pumped.

The gun smith recommended that the chamber be polished. Would this be a logical step in fixing the problem?

What sort of reason would one polish a chamber? I know it is to make it smooth but since the gun only been with family I'm having a hard time understanding how the chamber could go bad just sitting around?

I recall looking at the barrel and no sign of rust or anything on it from just visual inspection.

Chamber polishing is generally done when a chamber has gotten rough or pitted from lack of proper cleaning and maintenance. You may also  have your cycling problem occur when using certain ammo types. Estate cartridges iirc, are actually steel instead of brass headed shells. I have had them try to tie up an 870 when shooting it. All a matter of how tight or loose your chamber is, how the shell behaves in your gun, and how clean the chamber is. Properly done polishing can help a shotgun cycle correctly.  Just don't overdo it.

Its like sharpening a knife, I can use a file to sharpen my knife and have a good looking, uniform edge with no nicks in the edge. That will cut most things you would need to cut. I can then polish that edge with some 1000 grit and then dress with a leather strop and get an edge that you can shave with. Polishing the chamber removes imperfections in the surface you can't see and makes it function better.

I had to polish the chamber on my brand new 870, it wouldn't cycle the cheap aluminum cased rounds you find in value packs.

Did a little research and its a pretty common problem in 870's, tooling marks left in the chamber can cause case sticking. The aluminum expands more than traditional brass shells and its softness allows it to grab any imperfections in your chamber. Couple minutes with some fine steel wool and cordless drill did wonders for it.

I also gave my side by side cowboy action shotgun the same treatment. I can crack it open and throw empty shells over my shoulder with a quick flip now.

To answer your question, It could be just about anything from light surface rust to access build up of "gook". If its an older gun it may have never seen anything but brass shells and never exhibited the issue.

"chamber polishing" is probably on your gunsmith's list of things to do if he can't diagnose a specific problem. You chamber may or may not actually need "polishing".

Has he performed a complete disassembly and detailed cleaning/inspection? I would start with that before paying for work that may or may not solve your problem.

Buddy of mine just did this because Remington forgot how to fully finish shotguns and his relatively new 870 would not extract. Pretty much to make extraction easier.

In SASS matches, you need your shells to fall out of your side by each for a fast reload.  Polishing is sometimes required to make that happen.  

I do it with a brake cylinder hone and then use emery cloth around a cloth bore brush in a drill.  

I also did one that has a bit of surface rust when making my SBR.  I bought a cheap barrel to practice on and it turned out so well that I kept it.  You can also clean up the area in front of the chamber and do a poor mans "back bore".

Recently my Rem 1100 had some chambering issues.  The locking mechanism was too dry and the mating surface had too much carbon build up.  I guess I should clean it once in a while.

The gun itself is in great condition. I broke it down before shooting and give it a cleaning. The gun cycles like a dream at home and it appears to pass every function test I can discover. The gun smith even complemented on how well taken care the gun appears to be.

I'm just worried that chamber polishing would cause more damage than good but even I can't determine what would cause the malfunctions other than replacing parts which might be more pricier than simply polishing the chamber itself.

Don't use shit ammo in that gun and there is a 98.9% chance your problem is solved.  By crap I mean bulk promo ammo with steel bases instead of brass.

I agree with the concept he is applying a typical Express 870 fix to your model 12 because he does not know them.

Done properly, polishing the chamber is not going to harm any shotgun.

I searched for others with a Winchester Model 12 issue like mine and found threads speaking about polishing chamber to actually be a success.

I tried shooting a Winchester Super X #5 Turkey shot and some Federal #6 Quail shots. They both appear to have brass bases to them, and not steal. I made sure nothing on it had the word "steal" on it before shooting.

On top of that, I brought the shotgun to him stuck with the round in it. He managed to eject it and didn't mention anything about it being the wrong ammo.



I will have to trust the gun smith at this point and hope for the best. Thanks for the info on it.

Polishing is a no brainer anybody can do.  My daughter did it at age 9.

After you polish it run some lighter target loads like Winchester AA.  Start by loading one round at a time and firing that round.

This guy knows model 12's better then most.
https://m.youtube.com/watch?v=xNExqxqdF_Y

Then hit this thread, down a little ways is a good description of chamber ring issues.  Few others too that don't apply to you since your gun cycles when dry fired.
http://shotgunworld.com/bbs/viewtopic.php?f=12&t=207466

I read that thread (on shotgunworld) earlier and it was unhelpful because the TC never came back whether he was successful with the problem or not. Matter of fact, that post was the reason why I came on here and posted this thread.

One poster talked about the exact problem I was having but never came back if his gunsmith fixed it or not. I only hope he is alive and well.

I went ahead and contacted the Kirby fella on that thread to see if he can remember or if that TC ever contacted him in regards to it.

For ~$60 I purchased a 400 and an 800 grit chamber flex hone along with their flex hone oil from Amazon. My brother and I both run JM Pro 930s and he was having some ejection problems with his. He happened to squad with J. Miculek himself at the Ft Benning 3 gun match and was suggested he basically stick a spacer under the ejector spring to give the ejector a little more power. I bought the hones and over Christmas we polished the chambers on both of ours and our dads 930's. Glad to report hundreds of rounds of Federal bulk pack through all guns have run now with 0 issues.

So my POS 870 will cycle...