Some questions about JB bore polish

[TheOperator]

I'm having a small problem with my mosin-nagant and have some pictures to help explain.

I noticed that after cycling a few rounds there would be a build up of copper wash on the lip of the firing chamber, as outlined in picture number 1



I thought it might be from a sharp edge or metal file scraping the cases, because it caused marking on the casing as outlined in picture number 2



So after some investigative work I found the rough edge to be on the bottom right of the chamber lip at around 8 o'clock and took a file to it (very carefully so to get grind away too much and cause head space issues) and now it just makes a rough scrape instead of strong sharp scrapes as shown in picture number 3



While this is an improvement its still not perfect.
Here is my question.

How strong is JB bore polish as an abrasive? Would it finish polishing off any rough areas so my casings don't keep getting scraped? I have a copper brush and power drill, but no dremel, so I'm hoping I can just get a nice abrasive and roto-rooter the problem away.

Also, the casing don't get scraped when being pushed into the chamber, only when I close the bolt and remove the cartridge do the markings show up. Maybe that will help in the diagnoses of what should be done.

Thanks to anybody who can give me help/advice!

 

[VinceU1]

You might try getting a bore swab that is the right size for the case, chuck it up in a drill, apply JB to the swab and VERY SLOWLY polish the chamber with it. It won't take long, the stuff really does work quicker than you'd think. I mean in 5 second runs, then clean and then try a case again. That'll polish the entire chamber, not just the neck area.

 

[TheOperator]

You might try getting a bore swab that is the right size for the case, chuck it up in a drill, apply JB to the swab and VERY SLOWLY polish the chamber with it. It won't take long, the stuff really does work quicker than you'd think. I mean in 5 second runs, then clean and then try a case again. That'll polish the entire chamber, not just the neck area.

Do you think a copper brush will work just as well? I also have some thick wool brushes. Although I think the abrasive might just ruin the wool...

 

[yellowhousejake]

How do you know that the marks only appear on extraction?

Is the case not coming up into the bolt head soon enough? It might be the case head sticking on the bolt head so the case never levels out before it gets to the chamber. Check the bolt head surface and the extractor for smoothness/burrs/hooks that could stop the case from moving up out of the magazine and onto the bolt head before the case body meets the chamber.

Just a thought.

YHJ

 

[sloughfoot]

JB bore paste is non-abrasive. It does not remove steel. It only makes it shiny. It is basically clay in an emulsifier.

Valve grinding compound removes steel.

I am not expressing an opinion on using anything on any Mosin Nagant rifle. I am simply stating that JB bore paste does not remove steel.

 

[TheOperator]

JB bore paste is non-abrasive. It does not remove steel. It only makes it shiny. It is basically clay in an emulsifier.

Valve grinding compound removes steel.

I am not expressing an opinion on using anything on any Mosin Nagant rifle. I am simply stating that JB bore paste does not remove steel.

Wish you could've seen and responded sooner, now I got a 1/4 ounce of bore polish for nothing!

 

[TheOperator]

More pictures and ideas. Please respond if you know ANYTHING.



Here is another picture and something else I noticed.

At first I thought the small line was caused by the stripper clips I had been using, so I took a completely clean round to test on and the line still shows up.

I have a feeling the chamber might be smooth and whats causing the marking is excess pressure from the lip of the chamber pressing against the casing upon closing the bolt/extraction.

If this is the case I don't know what I can do to fix the problem aside from taking it to a gunsmith...

If anybody has had similar problems with any firearm before could you give some insight? Or at least tell me of some local gunsmiths who could fix this for cheap?

I didn't get my mosin simply from loving the gun so much (which I do) I have a shoestring budget here...