What is the cause of a "DARK BORE"?

A "dark bore" is normally used to described the bore of a rifle that fired corrosive ammo and as a result of not being properly or thoroughly cleaned, the bore is not bright and shiny.

A dark or "frosted" bore is not a deal breaker. I have a K98 Mauser with a dark bore and it shoots very well.

My Mosin Nagant has a dark bore and it's pretty accurate.

"What is the cause of a "DARK BORE"?"

Rust.


"Is it safe to shoot with full power cartridges?"

Yes.


"Will it wear out faster than a normal bore?"

It's already worn out...



Really: Mechanically it'll not wear any faster than a clean bore, and it'll probably shoot just fine. Ignore it and press on.



Willie

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Willie Sutton said:

"What is the cause of a "DARK BORE"?"

Rust.


"Is it safe to shoot with full power cartridges?"

Yes.


"Will it wear out faster than a normal bore?"

It's already worn out...



Really: Mechanically it'll not wear any faster than a clean bore, and it'll probably shoot just fine. Ignore it and press on.



Willie

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I do not see if a bore was rusted where it would be worn out. This can happen to a new gun. I have cleaned many old rifles that were rusted / dark bores and they shot fine

A dark bore can mean anything from fouling to corrosion. It can be caused by any type of ammo or lack of proper care. I have dark bores that shoot well and dark bores that are crappy. If you have a dark bore with good rifling it will must likely shoot about as well as other rifles of the same type with shinny bores. If you have a choice always go for a shinny bore.
A black corroded sewer pipe bore is best left for someone else

How is the rifling?

8-10 years ago I noticed in the SGN that SARCO had some "Dark Bore" Yugo-scrubbed K98ks for $110(?).

I had an excellent-bore K98k takeoff barrel in my kit that needed a new home, so I ordered one of the Yugo K98ks.

On first glance, it look like something had been living in that bore ... nasty ... but ... I cleaned it thoroughly and, even though it was still quite fugly, there was noticeable rifling and the muzzle gauged well ... so ... I took it out to the backyard and test fired it ... and it is surprisingly accurate, especially for the look of that bore.

So I had to order a 2nd Yugo K98k for my barrel swap project ... and this one sported a tomato stake bore, so then I had 2 more k98ks rather than one.

In direct answer to the OP's questions, corrosion makes this bore dark, but it can still safely handle full-power cartridges. And, yes, I would expect a dark bore to wear out before one that is still mirror bright ... but we are talking about a LOT of rounds.

Now that I have been thinking about that episode, I am going to have to pull that dark bore Yugo K98k out of the gunsafe an exercise it a bit.

Sometimes steel darkens when it's over-heated as well.

I had a .303 than had been sporterized (what I call a "California stock' monte carlo cheek piece and all) that had shiny lands but dark grooves and figured the grooves were dark because pitted from hot cordite and corrosive primers, based on all I had heard about surplus Lee Enfileds. After shooting it with sporting ammo I would clean the bore reasonably well and put it away. Always got green on the patches when I wiped the bore dry before firing on the next outting.

Then I tried some black powder handloads with cast lead bullets for the local black powder cartridge match, and gave the gun a cleaning workout, and decided to use some Sweet's 7.62 high ammonia solvent. As expected I got a lot of crap out of the bore, but when I looked down the barrel I had bright lands and bright grooves.

My experience has been that dark bore may indicate pitted bore, or it may indicate a bore with stubborn fouling and under the fouling the bore may be good or it may be pitted. Only a thorough cleaning will tell.

"Dark bore" = euphemism for a rusted bore, although maybe not to the stage of noticable pitting. I think this is a term concocted by sellers, years ago, to make what they were selling not seem so bad. Same rationale for "frosted bore." A "frosted bore" means light pitting.