SKS - 8% of rounds key holing

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armycat

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I purchase a SKS from Canadian Tire. It's a late production Tula that has been refurbished. I have modified the rifle to use Tapco magazines and have modified the bolt to permit the magazines to be inserted or removed with a closed bolt. The rifle has functioned flawlessly but only has about 70 rounds through it.

Today I went to sight it in. I set up a targets at 100 yards. The first 12 rounds were off paper. The next 24 rounds were on paper. 22 hits appeared to be nice round holes, 2 were key holed with the bullet going through the target sideways. That's 8% of the on paper hits key holing.

Ammo was Barnual 123 gr FMJ. I did not examine it closely but did not notice any defects. I checked 40 more rounds afterward and they show no signs of defect or corrosion. I did not notice any difference if recoil, muzzle blast, etc during firing.

Rounds key holing can be caused by several factors (as I understand it)
1) worn out rifling
2) rifling twist not adequate for the bullet length/weight
3) bullet undersized and not engaging the rifling adequately
4) leading in the barrel
5) damage to the barrel or crown

Number of rounds fired is pretty low so the 8% may not be an accurate number. It seems to me that worn out rifling or damage to the barrel or crown would result in a higher number of rounds key holing. There is no damage I can see. Rifling twist rate should be adequate. i would assume that undersized bullets or leading is the problem. When I bought the rifle the bore just received a quick pull through to ensure it was clear of obstructions. When I cleaned it tonight it was filthy but only seemed to be carbon, no odd colours on the patches.

I don't have a scale accurate enough to weight the cartridges but I will measure 60 for overall length and bullet diameter. The bore has been scrubbed clean. Hopefully I can hit the range this week and see if there is any change. I have some MFS FMJ so I will give them a try as well.

Is there anything I am not considering?
 
if you can hit something the size of a pie plate with a sks at 100 yards , you are doing well .... :D

if it has a chromed barrel , you don't have barrel issues .

a 2 second inspection will tell you if you have worn rifling or a damaged crown .

and finally fmj ammo is designed to tumble on impact ( since it is illegal for it to expand like hunting ammo in combat ) .

so they make it as unstable in flight as possible , while still being able to hit a pie plate at 100 yards .

while the bullets maybe key holing , there is a good chance they are supposed to be doing that .
 
Try differnt ammo, I hear LOTS of bad stuff about some batches of barnaul.

Seems like the most simple thing to try first before you start messing around.

Also, Make sure the gun sits in its stock good.
 
You won't get leading with Fmj ammo, as was said, try the ammo it was meant to fire! was it cleaned very well after you bought it?
Did you try it in the stock that came with it? The SKS was made for a projectile of approx 123 gr. So that should not be your problem. I haven't used Barnaul but as was said above, may be your problem,, check your muzzle! With that many misses, is there a burm or something you may be nicking between yourself and the target? What did you do to the bolt/ carrier?
 
It wasn't cleaned very well. Scrubbed thoroughly last night. Fowling may have been the issue.

Will try MFS 7.62x39, unfortunately that's all I have available right now.

The rifle is in its original wood stock and seems to be sitting securely with no issues fitting in the stock.

No modification to the bolt carrier. Bolt was modified by grinding off the bottom rails that engage the magazine lips so that magazines can be inserted and removed on a closed bolt. Using Tapco 5/30 magazines.
 
One quick test you can do without shooting is the "bullet test". Take a cartridge and insert the bullet into the muzzle. It should not go in all the way to the case mouth. If it does, the muzzle, at least, is worn to the point of being oversize.

If it passes this test, I would try the other ammo type. It is unlikely that you would get keyholing with two different types without the barrel being somehow defective.
 
Keyholing is definitely not normal behavior even if it is a "$200 milsurp rifle". Shot about 300-350 rounds of good old commie corrosive surplus through my Norinco and haven't ever seen evidence of keyholing up to 300 yards. Either your barrel has some kind of damage or your ammo is trash.
 
tjhaile said:
One quick test you can do without shooting is the "bullet test". Take a cartridge and insert the bullet into the muzzle. It should not go in all the way to the case mouth.
Click to expand...

Did that, even with a slight pressure there is about 3.3mm of bullet jacket visible between the muzzle and the mouth of the cartridge case.

Hopefully tomorrow I'll be able to hit the range and try out some MFS ammo.
 
armycat said:
Did that, even with a slight pressure there is about 3.3mm of bullet jacket visible between the muzzle and the mouth of the cartridge case.

Hopefully tomorrow I'll be able to hit the range and try out some MFS ammo.
Click to expand...
Yea pretty hard to burn out an SKS especially if it is refurb as it should have been measured at the factory and if it was out of spec, a new barrel would be put on. Good luck with the different ammo, if you can get your hands on some surplus try that.
 
The two key holes were almost perfect sideways bullets IMO.

Hits on paper, holes a fairly round so I think they were stable when they hit the target.
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One of the two key holes. Wish I had taken a photo of the hole with a bullet beside it for comparison.
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I'm guessing damage to the Crown, but that's pure speculation. That said, my friend had a SKS with the same issue and his crown was to blame. Got it turned and it was 100 per cent better.
 
Several years ago I had some 8mm Mauser surplus from Israel that keyholed like that occasionally. They didn't feel any different as far as recoil went but they definitely sounded different. If your ammo weren't new I would suggest deteriorating powder or primers causing lower velocities causing your bullets to destabilize. Another time I had an issue with brand new in the box 225gr, 338 Win Mag in Red Federal boxes. The issue there was caused by bullets separating their cores from their jackets.

I doubt any of the examples above could be the cause of this.

It's interesting though and if you do find the cause of this please let us know.
 
In the mid 90's a friend and I were firing surplus Norinco 7.62 x 39 20 round boxes through my SKS. Was shooting at a 30" gong at 200 yards which lay against a dirt hill which allowed me to determine I was missing target by 6-8 feet in multiple directions. Couldn't figure out why I had to rack the bolt back after every shot. After having a WTF moment I got my friend to try and spot the rounds as they were being fired. The rounds were moving so slow we could see the bullets tumbling in flight and my friend started to call the shots before they reached the 200 yard line. He was laughing so hard we had the entire line watching the bullets go downrange and commenting on the fact they never had seen this before. After two boxes the rounds starting impacting on the target and everyone settle back down. Sometimes you get a bad batch. Note - I was pretty careful firing only one shot at a time - confirming the tumbling round made it downrange - before touching off the next round. Fired 1000's of rounds since then and have never had a repeat.


L
 
armycat said:
The two key holes were almost perfect sideways bullets IMO.

Hits on paper, holes a fairly round so I think they were stable when they hit the target.
image.jpg1_zpswhlxjlt6.jpg
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One of the two key holes. Wish I had taken a photo of the hole with a bullet beside it for comparison.
image.jpg2_zpsr7el0w4p.jpg
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Click to expand...
I see what may be at least 3 bullet holes there! Maybe your grouping is better than you think!;)
You would think if there was a problem with the crown or barrel, you would get more keyholes and tumbling holes ! Most holes are perfect! Try the other ammo but it may just be a group of hits if not then there may have been a bad batch of ammo!
 
Hit the range today, unfortunately in my haste I forgot the 60 rounds of Barnual 123 gr FMJ I had set aside. I had 20 rounds Barnual 123 gr FMJ and 20 rounds MFS 123 gr FMJ in my range bag.

After my last range trip I scrubbed the barrel using multiple types of solvents. It was filthy but the patches just seem to have carbon on them, no rust or strange colour corrosion.

I fired the 40 rounds at 100 yds and all hits were clean through the target, no signs of key holing or unstable rounds. Seems the culprit was excessively dirty bore or two faulty rounds on the previous trip. I cleaned the rifle afterward and it was dirty after 40 rounds but not nearly as dirty as it was after the last range trip.

I still intend to run another 60 Barnual through it to see if I have any more key holes.
 
armycat, most people clean their rifles after every 20 rounds or so. Some never clean them and it usually shows up on the targets.

The SKS may not be a precision rifle but it is a very functional system that does everything it was designed to do. The biggest deterrent to function and accuracy is jacket fouling and carbon residue. Pretty much the same with all rifles.

I find I can get away with around 50 rounds through the SKS I shoot before the groups start to open up. With milsurp ammo 4in at 100yds is normal. With Federal white box and some Chinese yellow/silver box 2-3in is normal. Select hand loads a bit better but not enough to bother with. My rifle has a pristine bore. I am sure as the bore wears the groups will open substantially.

Good luck with that rifle and get yourself a bottle of WIPE OUT. A couple of passes with a soaked patch, leave it sit for a few hours and repeat. Clean out the next day and you will have a bore clean to the barrel metal without fouling. Make life a lot easier. Most good gun shops carry it. Google it if you can't find any.
 
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