SKS w tight spots in bore?.

[chill45100]

A recently purchased SKS was bore slugged and several restrictions were noticed.
First of all the rifle- a Norinco with a 16.5 inch barrel, aftermarket plastic stock and hand guard.
Slugging method- an oiled piece of 00 buckshot was pushed and driven through a well oiled bore using a cleaning rod just able to pass through the bore.
Findings- once the shot was started into the chamber three were 3 tight spots. Just forward of the chamber, at the muzzle end of the hand guard and about 1 1/2 inches from the muzzle. When the slug was measured there was an oddity. One diameter was .310-312 but the other was .308-309. Which makes me think the grooves were not cut to even depths during rifling. Possible?? Or is a localized restriction more likely?? My eyes cannot see the cause. The bore was slugged three times with consistent readings on my micrometer.
Questions- would this rifle be safe to shoot? Yes there was powder residue in the bore when it was cleaned prior to slugging meaning it had been fired although I have no idea if done before or after the barrel was cut down. Would fire lapping be a potential benefit? Finally is this particularly unusual in a Norinco SKS?

Thanks,
chill45100

[fatelvis]

Does the rifle have a chrome lined bore?

[725]

I'm sure there is more to the story, but I'd fire lap that rifle with hard cast boolits. No need to have a powerful load. Just enough to fully function the action. Try one firelap and inspect. Try another firelap and inspect. Once you are confident all is working OK, I'd fire groups of 10 or 15 with the abrasive and see how much things change. Go slow as it's easy to remove metal - not so much the other way around. In my experience, I have had wonderful results in fixing messed up barrels by firelapping.. YMMD

[chill45100]

Fatelvis- Not sure about the chrome lined bore will clean more and try to figure that out. Any hints on how to tell?

725- will get some hard cast bullets and try fire lapping.

[leadman]

A Norinco SKS should be a chrome lined bore. My Norinco is chrome lined with some chrome peeking out from the bore at the muzzle.
From what I have read the only non-chromed bore is on the Yugos.
Do the tight spots line up with sights, gas blocks, etc on the outside of the barrel?

[chill45100]

Leadman- yes except for the now relocated front sight. The third tight spot is ahead of the gas port a couple of inches.

[Bloodman14]

If the tight spots coincide with the gas block, sight block, and piston block, firelapping should smooth them out.

[fatelvis]

Fatelvis- Not sure about the chrome lined bore will clean more and try to figure that out. Any hints on how to tell?

725- will get some hard cast bullets and try fire lapping.
Leadman is right. If it is a Norinco, it is chrome lined. I think the chrome lining is going to prevent effective firelapping. But it's worth a try. Please keep us posted!

[chill45100]

Thank you one and all for your input. I'm scrounging up some hard cast bullets, brass and a set of dies to begin fire lapping.
If the chromed bore does not allow the best of results, oh well. At least the components will be in the cabinet to load with. A fire lapping kit is already in hand.
And yes results will be posted.
chill45100

[chill45100]

I've fired 5 rounds of 220 grit and 8 rounds of 330 grit coated hard cast bullets cleaning well between grits. The only tight spot when pushing a tight patch through the bore is at the front sight. Where it was relocated and welded in place. Now to fire the fine grit (600?) for a final polishing. More to follow.
chill45100

[30calflash]

I'm unsure if I'd fire lap it at all. Could reduce the thickness of chrome plating and having that cause the chrome to flake could be a major issue down the road. It is what it is, shoot it and go from there.

[Garyshome]

Great thread. I have a mosin that needs fire lapping.

[Quiettime]

... Could reduce the thickness of chrome plating and having that cause the chrome to flake could be a major issue down the road. It is what it is, shoot it and go from there.

The chrome in the bores is quite a bit tougher than say a chrome bumper. I've seen more than one mention of cutting barrels down or re-chambering chrome lined bores without flaking.

And yes, sight pins and handguard pins make speed bumps in the bore, thats why target type AR15's do not use pins, but rather clamp-on or set screw sights/gas blocks.

Quick google search returned this:
http://www.m-guns.com/tool_new.php?product=reamer


What about chromed-lined chambers? The good news is that in my experience, Colt AR15 chromed barrels have a proper 5.56 chamber. I would consider most others to be suspect. The reamer has been subjected to a secondary heat-treating process, titanium carbo-nitride, which makes it capable of correcting under-spec chromed chambers. Obviously it will do fewer of them, but I have yet to hear of one of my reamers geting dull-- and my personal one has done at least a few dozen chromed chambers. Will removing the chrome be a problem? No. Plenty of AR's don't have chromed bores and chamber and they work fine. I've sectioned some chromed barrels and the chrome doesn't last that long in the throat area anyway. Removing chrome in the chamber won't cause the area to peel like bumper chrome.