Borescope Interpretation of a 70 year old rifle

To my eye looks like some kind of build up ....try cleaning it?

Looks like rust to me.

Use a bronze brush and a good bore cleaner.
You might need more than one brush

Back then ammo was corrosive. No putting would be stranger. Have you shot it? If you are happy with the groups, doesn't matter.

My guess.... future pitting.

If you clean it aggressively, or shoot it, those little rust clumps will wipe away and leave behind pits.

That is pitting and there is zero you are going to do about it, material is missing and its not coming back .
The rifle will most likely shoot fine and may be just as accurate as a perfect bore but it will accumulate copper
and carbon more.

Shoot it. It may shoot great. Or, it may not have shot very well all even when it was brand new? Who can say.

I have more than a few pitted, very pitted, to horribly pitted barrels that shoot great. They just take a little more effort with cleaning and maybe a learning curve to figure them out. (how much , how often)

What I would do it shoot 25 or so rounds thru it then look at it again. IMO what is there is going to have zero effect on accuracy or barrel life.

That is likely rust, with underlying pitting that will visible once the rifle is shot/cleaned. Will take more effort for cleaning, and may be tough to get fully clean, but may still shoot just fine.

Just shoot it

I had an older 700 that looked horrible. It would take 5-10 rounds to start shooting good, and would only hold it for 50 ish rounds. Then groups opened up again.

So, while it was still just fine for hunting use, I put a new barrel on it.


Nothing you can do about it. So if it doesn't shoot it needs a new barrel. If it does shoot you'll need a new barrel anyways.

That barrels wrecked, and will throw fliers BUT, I have a few rifles, 1 with the same exact bore you have, and 2 more that have REAL bad bores, and surprisingly they all shoot pretty dam good with handloads lol. At a hundred, I can keep em inside of two inches, and the one that looks like yours, is a one moa gun believe it or not (yugo m48)
What I did to mine was clean the SHIT out of them, which actually takes a few hours, then I shot the Tubb lapping bullets through em, and surprisingly now they shoot pretty good. Granted those bullets only actually cleaned up the first third of the bore, but they did actually help my groups. Unfortunately for your milsurp, that's the exact caliber that if on the higher tolerance of bore diameter, does not have a decent selection of bullets to try out (higher end of .312", which some are .313" ID) for a good bore/bullet seal. I'd still try er out though.
Try some Norma brass with the .312 Hornady 150 gr flat bases or any of the heavier .311 copper solids at inside of 300 yards.
These wrecked barrels copper and foul BAD, and always need 3 times the amount of cleaning as all my other barrels do, but I'm currently in an experiment where I just go after the carbon and leave the copper, to see if that helps with gas seal.
For your initial clean, wet it in butch's bore shine and let it sit for a couple of minutes, then attack it with a steel bristled brush a few strokes, then wipe all that out and continue with the normal bronze bristled brushes.