The bore on my recently acquired sporter Krag carbine looked like it had not been cleaned in 50 years.  Fortunately, the lands look good even if the grooves seem to have an accumulation of buildup.  I have worked in solvents and brushed a good amount with some little improvement.  The grooves seem almost lumpy rather than rough, but not smooth. Near the chamber, the grooves seem to have a stubborn buildup under "down hill" edge of the land and up to its top.  I detect no throat erosion.  At present the bore is soaking in Kroil.  I will brush again, but I wonder if some shooting might loosen up the junk in the grooves.  Can some of the junk be shot out?  Has anyone has success in cleaning up these old bores?  Is there a better way to do this?  I am really looking forward to shooting this dignified old rifle and am really pleased that I have it.  Thanks for your help and advice.

My experience:  I've always bought used guns paying special heed to bore condition.  Occasionally, I've risked buying a gun with a 'dark' bore.  A couple of times the darkness was old cosmoline and I was real lucky.  Usually, the darkness was rust.  I seem to experience four kinds of bores:  1. Mint and shiny.  2. Shiny and a bit worn.  3. Shiny with minor darkness, pitting, or erosion.  4. Dark, with no amount of elbow grease and cleaning agents showing improvement.
     All four of these bore conditions may shoot well.  The first three clean and eventually provide clean patches.  The fourth category never cleans and provides infinite black cleaning patches.  It may also shoot very inaccurately.

Looks like mine is about a 3.  I'll try working on it some more and shooting it.  My first look down the bore from the muzzle with a patch in the back of the receiver, to catch light, showed a completely dark bore.  It turned out someone had shot a 30-30 in a 30-40 and the ruptured case was still in the chamber since the extractor would not pull it out.  This dignified old rifle was a gift from an old friend and I will treat it with respect.  Generations ago someone made a carbine from an 1895 rifle with 22 in barrel, shortened forearm with schnable fore end a internal barrel band, added a pistol grip, skillfully, and a butt pad.  Thanks butlersrangers for your response.

I think I may have a #4.
After corking the chamber and soaking in solvent, stroking many time with SS brush and other suggested methods, I'm afraid to shoot this old girl.

More to follow.

Ooops, looks like I need to know more about image posting.  Sorry.

The CMP sells Criterion barrels and is now offering some gunsmithing services at Camp Perry and Annison.  This may be an option worth exploring.

Thanks Butler.  I did buy a used barrel to replace mine. It's at the gunsmith now. I was interested in the forums reaction to the photo, but I haven't mastered succesful posting of photos stored on my computer.

ButterBolt:  Tell us more about your "used" Krag barrel.  I hope the project turns out good for you.  (Hint regarding photos - I take mine at .3 megapixels for posting, steady hold and sharp focus is critical).

I picked up a scoped 98 Krag with a #4 condition bore as described. I think it was fired with corrosive ammo and put away uncleaned for decades. I used Hoppes #9, Sweets 7.62, Kroil, JB Bore Paste and Bronze wool on the bore. The bore is still dark and patches still come out with some black on them.

The rifle still shoots cast bullets in 5 shot groups of 1.5 inches or less at 100 yards. Amazing!

This is the original barrel from a unmolested Krag I purchased. I didn't think it would be a "shooter."
It looks like something was run down this bore spinning, as there are swirl marks not in coincidence with the rifling present.  Lot of deep pits etc.
Went looking for a better old barrel and found one on line.
When I get it back from the smith and test fire, I will post results.

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Another photo of the barrel. (not)
A real sewer pipe.

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That picture looks terrible.  However, all may not be lost...

Believe it or not, some of the so called "sewer pipe" Krag barrels are capable of producing fairly good accuracy with jacketed bullets.  The pitting and garbage will make mincemeat out of a softer cast bullet, but the copper jacket is less susceptible to picking up crap as it travels down the bore.  As long as the barrel is safe for shooting (no cracks, bulges, or other dangerous damage), you might hang onto it...  Fire a couple jacketed rounds through, and see what she does.  You might be surprised.

ButterBolt:  I am not computer tech savvy.  I store my pictures, for posting, at low resolution (.3M digital camera shots) on my computer hard drive, as photos or documents.  When I am making a posting or reply on the KCA forum, there is a 'Browse' button near the bottom of the window.  If you left click on this button, you are taken to your images in the Documents library.  Select an image and left click on the 'Open' button.  You will be returned to the message window and the title of your image will be in the Browse box.  You can then post your message and one image by left clicking on the 'Post Message' button.  If you attempt to  'Preview' your message and image, you will lose the attachment and have to go Browse for it again.  If the image has too many pixels, you will get a 'posting error message'.  (Wow, I just learned to use the 'Attachments+' box to add another image to a posting)!

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Thanks for that. 
Good description.
I saved it in case of memory failure.
I think I went astray on what I have seen "insert" and "attach" functions do, elsewhere. 
And ofcourse, I was trying to do 2 photos at once.

ButterBolt wrote on Feb 7^th, 2014 at 3:12pm:

Another photo of the barrel. (not) A real sewer pipe.

;D

Barrel replaced with older but better one.
Pics of old vs new.

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Replacement.
Forum, is that sharp rifling?

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That's pretty sweet looking!  Well done!

Wow...night and day.  I'd buy any Krag with a bore like that in an instant!

Finally got around to slugging the bore on the new barrel.  I read in old KCA posts that a 00 buck shot is .033.  So I started one through and notice it was tight enough for the first 4-5 inches, then loosened up.  It measured .030 groove to groove and .0309 on the high spots.  I'd like to use a slightly larger ball or slug.  Any suggestions?

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Another pic.

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Use two rods with the balls you have.  Start it in, use one rod as a stop against something solid, use the other rod for smacking the ball so that it expands out into the rifling.  Push it back out the end you went in.  I use some store bought brass and/or steel rods, not a cleaning rod.  If you're planning on shooting cast, size them .311 if the neck will permit it.  Some modern brass I have will allow me .311, some older stuff, REM-UMC 30USA will only allow me .310.  Slug both ends of your barrel, sometimes you run into a reverse taper with the groove diameter getting bigger as you go toward the muzzle.