AK Malfunction Troubleshoot - Yugo M70

[Hanzy4200]

I picked up two AK's this week from a friend on hard times. Didn't haggle, but the deal was decent. A Zastava M70 underfolder, a WASR-10 with Tapco furniture, 2 steel mags and 100 rds of Wolf HP. $1,050. He told me the Yugo might have had feeding issues, but he wasn't sure as he hadn't fired it in years. To the range. WASR shot like a WASR. Gritty trigger (pre G2), moderate accuracy, stinging cheek recoil, and ran 100%. The M70 not so much. Trigger is great, recoil is surprisingly mild and smooth. She malfunction about every 3-4 rounds. See picture. I tried a surplus steel mag and brought a PMAG as a control. No difference. Any ideas?

I stripped it down, and the action was pretty clean. Gas system appears fine. There's a bit of bolt drag on the hammer, as most have. I polished it up today anyway. It also got a stuck case, which I pounded out. I soaked and re-scrubbed the chamber.

[Castaway]

What was your malfunction? Failure to feed, failure to fire, failure to extract, or failure to eject??

[358429]

Look at the fired casings for more clues.

[Hanzy4200]

Failure to feed...........

[Moleman-]

Bolt over base is generally under gassed or too much friction somewhere.
If it is a M70 built from a surplus kit and has the grenade launching shut-off valve/sight on the gas block, check to see if the gas valve and gas block are corroded. For whatever reason the original military Yugo's didn't have chromed barrels, gas blocks or gas valves. The yugo dark bores are well known, but the gas valves and their bores corrode and let the gas leak by. On one of my rewelds the gas valve spindle would move about 1/8" on one side of the gas block and about 1/16" on the other. The valve spindle was significantly corroded away and the bore for the spindle was corroded out to oval in shape. Initially it was tight and worked correctly, but soon the hot gas blew enough of the rust away that it started short stroking. They could of stopped it from happening by chrome lining the block and spindle, but they didn't.

Fixed mine by reaming out slightly larger and making a new valve spindle.

Pics start of receiver welding, gas valve before thinning the head and nut, and put together rifle enough to test fire and have the corroded valve rear it's ugly head.

The other thing to check is the gas port to see if it is aligned with the gas block or not. The port should be around 1/8" ish and you need to have the grenade sight down so the passageway is open in order to check which means you need a long 1/8" bit.

Check to see if it is hanging up on the hammer tip or ejector. The chamber could also be very rough.

[AndyC]

Bolt-over-base malf's are usually induced by:

1. The round not lifting high enough to be caught by the bolt because:
a. Rifle is undergassed - the bolt doesn't go all the way back and the cartridge is still in the process of rising up from the mag while the bolt goes forward early.
b. Magazine is damaged, slowing the rise of the cartridge - dented mag, dirty mag slowing the rise of the follower, weak mag-spring, etc.

2. The lower edge of the bolt is worn round, not a flat edge to reliably catch and press against the case-head from behind; it slips over the case-head and hits the body of the case instead.

[Hanzy4200]

I now believe it is either due to hammer drag on the bolt, or it is undergassed. I have noticed the hammer drag is significantly more pronounced than usual. Century built AK's have this, I know, but it seems worse than usual. I broke my own rule, and pulled out the dremel. I used some fine grit sandpaper, and some rough jewelers polish on the dremel wheel. I polished the surface of the hammer, and lightly on the bolt also. I was pretty conservative. I can feel a significant difference when working the action. Much smoother. I will take it out this weekend and see if there is any improvement. As to the gas issue, I have no idea how to remedy that.

[Moleman-]

I'd be surprised if there weren't several youtubes about polishing/recontouring the hammer to prevent the bcg from hanging up on it. Many of the aftermarket hammers have this issue.

Try working the action without the hammer installed to see if the bolt is dragging on the ejector as well. Sometimes they get bent slightly and it takes more effort for the bcg to go over them.

For the gas, if yours has the grenade launch gas block check to see that the valve isn't corroded. If it's fine, check the gas passage. The valve/sight needs to be down so it's in the regular fire position with the bcg and upper handguard and gas tube off. You should be able to stick an 1/8" extended "aircraft" type bit all the way down through the gas block into the bore. It's also possible that whoever built the rifle drilled the gas port at 90 degrees to the bore. If you can't get an 1/8 bit into the bore or a piece of coat hanger wire won't fit through, check for that before trying to open it up.

[dkf]

What ammo did you try in it?

[waksupi]

Remove the bolt and look at the gas piston. Is it straight? I helped make 5500 AK's US compliant, and many were very crooked. We would whack them on the bench to straighten. Makes a difference in function, as a crooked piston creates drag and slows the bolt. .

[Tonto]

I had one that appeared to drag the underside of the action cover, confirmed with a coat of graphite spray and partially solved by that too. Just enough to cause unreliable feeding somewhat randomly with factory ammo.

[porthos]

go to the gunsmithing section

[Hanzy4200]

What ammo did you try in it?

So far I've tried 4. Started with Tula, Wolf, Golden Tiger. Last week I broke out the good stuff. Yugo surplus brass cased. This seemed to slightly improve things, but only marginally.

[Moleman-]

You've tried different magazines and ammunition. Have you checked for binding at the: ejector; piston; bolt carrier as it passes through the rear sight block; center support; or rails as well as gas port alignment and size as well as gas valve condition yet?

[archangel2003]

Also, if the receiver hole is sloppy or loose and all the magazines are sagging just a little, it can cause the bolt to ride over the bullet as well.
my bet is it's probably under gassed.
I manufactured a new hammer spring from scratch and used the same diameter wire twisted and bent to duplicate the soviet one and it is much stronger (probably higher quality music wire) than the stock one and it will act as a bolt hold open if I let the BCG loose easily by pressing the hammer to the bottom of the BCG, but never caused an issue when firing.

[1Hawkeye]

Another thing to check is to make sure there's no grease in the tube the gas piston rides in. I've seen several ak's and a couple of sks's short stroke because the owners didn't properly degrease them before use. What a mess to clean out once it was mixed with a couple hundred rounds of powder fowling.