Tuesday, December 13, 2005

SKS mods, and a fix for a problem

A while back a Very Helpful Commenter(hereafter known as VHC) mentioned that he'd taken some of the Yugo 59/66 SKS rifles and cut down the barrel to make them shorter, lighter and handier as a truck/car rifle. He sent a couple of pictures and has given permission for me to post them.

DISCLAIMER!! He had good luck with this, and the one I tried it on is working nicely. That does not mean you will have no trouble! This is not a hugely difficult project, but there's a couple of points that could cause a real problem later on if you don't do it right.

With that over:
If you're not familiar with that model, it has a grenade launcher and sight mounted to the front and that end looks like this:

(I'm going on the description party by memory, as one of the side effects of losing my old PC was losing the e-mail that described his process)

What he did was a: take off the launcher and bayonet, b: remove the front sight assembly and cut off the forward extension, everything behind the sight base itself and the bayonet mount, c: re-mount the front sight.

Start by stripping the rifle, including taking the barreled action out of the stock. Pull the screw the bayonet pivots on and it comes off. The launcher is screwed onto the muzzle and pinned; drive out the pin with a punch. Use a vise with padded jaws to hold the receiver(if you have/can make some curved pads to hold the barrel tight enough, go ahead). Then, if you're not worried about the finish of the launcher, grab it with some vise grips or a pipe wrench; if you want to protect it, use some leather or something as padding. It's a standard right-hand thread; I'd suggest get your whatever locked on and give it a sharp blow with a piece of metal rod or pipe, after which it should unscrew.

The sight unit is held in place with two pins(on those I've seen), so drive out the pins, and the piece comes off to the front(note: I took all the pins out at the same time). Put a little oil on the barrel in front of it; mine I was able to twist back & forth as I pushed forward, some may be tight enough to need moving with a wood block and a mallet. Once off, you can do what VHC did and cut off everything in front of and behind the sight base itself:

Or you can do what I did; since the flip-up night sight still had some glow left I decided to keep it. So I cut off the rear section just behind that:

If you cut as much off as he did, you lose both pin holes; if you leave the night sight section on, you'll still have one. To take the launcher sight off, the easiest way is to bend one leg out to take the sight off the pivot pin, then cut/file the pin off flush on both sides. I, for some reason, decided not to do that and drove the pin out. This pin also holds the night sight in place, so I had to put the damn thing back in.

Whichever you do, you now have to decide how long you want the barrel to be. You could leave it the original, threads and all, or cut it back. VHC wanted it short, so he drove the sight base as far back as he could-taking care to keep the sight as vertical as possible- and then drilled through the lower curve of the base and barrel for a new pin.

POSSIBLE SERIOUS PROBLEM If you do this, make DAMN SURE you don't go high enough to either drill into the bore, or too close to it; if you cut into the bore all you can do is move the sight back beyond that point and try again, which will mean either milling/filing/sanding the inside of the base larger so it'll fit further back or cutting down the diameter of the barrel to allow the base further back. And if you're too close, it could possibly cause the barrel to bulge at that point during firing, which may or may not cause a dangerous failure. So take note of exactly how deeply the original pin notches cut into the barrel.

After he set the sight in place, he cut the barrel off a little in front of the base, then filed it square and crowned the muzzle. I'm not going to cover some of the how's of that right now.

POSSIBLE SERIOUS PROBLEMS You could, by opening up the sight base a bit, move it as far back as just in front of the gas block; two things wrong with that. Cutting it back that far might affect the functioning of the action by changing the gas pressure that reaches the system, and it could make your rifle illegal. Remember, the minimum legal length of a rifle barrel is 16", which(according to the ATF agent I called and asked) is measured from the bolt face to the muzzle; by my measurement if you move it all the way back you'll be a bit below 16. So if you decide to do this and move it way back, measure it and make sure you leave the barrel at least the legal length.

I decided to use the original pin hole in the barrel, so the sight stayed in the original location. I marked the barrel about 1/4" in front of it, cut it off and crowned it, which gave me a barrel just under 19". Then pushed the base back into place and set the pin. If your pin doesn't feel tight enough, put a drop of thread locker on before driving it in. And it's done.

It's amazing how much lighter and more balanced it feels now. VHC says he's never had a problem with the action functioning. I did, but that was before the mods, which brings me to

The SKS Fix

I found out there's been a lot of discussion on various gun boards about this model SKS not functioning. As in it fires, but the action either doesn't cycle at all or only partially does, resulting in either stovepipe jams or incomplete ejection. Not good in a rifle at all, but especially bad in one you might have bought as a 'just in case' firearm.

The problem seems to be mainly(maybe entirely) on the 'shooter grade' rifles. 'Shooter grade' all too often seems to mean 'was rode hard and put away wet, but they still go bang!'. Often bores are worn or somewhat pitted, and- the big problem- the gas valve and/or tube is worn or corroded badly. This model has a valve that in the normal position causes gas to flow into the tube and work the action; in the other position the gas system is cut off so all the gas from the blank goes into launching the grenade. The valve fits into the gas block and the gas tube fits onto the end of the valve, so you have a couple of places where wear or corrosion can cause a lot of gas leakage, quite possibly enough to cause your SKS to become a straight-pull bolt-action. If it were the gas tube at the end, a new tube would fix it, but from what I've heard it mostly seems to be the valve itself. I thought of a couple of things that might fix it(other than a new valve; they seem to be hard to come by). One was to get some shim stock and make a sleeve for the valve to fit it more tightly into the gas block, which would do it if the valve body or inside of the block were eroded. Or, do something to make the end of the valve fit the gas tube more tightly.

There's a lip on the end of the valve that looks like it should have some kind of seal on it(it doesn't, but it looks like it) so to see what would happen I found an 'O' ring the right size, put it on and headed to the range.

Perfect function, empties thrown like a frat boy throws an empty bottle. For about 35 rounds. At which point the ring fell apart; didn't seem to hold up too well exposed to the gas stream. So I got a piece of thin, flat steel bar stock, cut a thin strip, did some sanding and made this:

Took some filing/sanding to get it the right thickness and width, but it fit into the lip and the gas tube fit on snugly. And it worked great. Action cycled with no failures. The empties were not flung as far as with the o-ring or a rifle without the problem, but as VHC put it that may be a feature, not a bug; enough gas leaks that the action does not cycle as hard, which means a bit less pounding and stress on the bolt carrier and receiver. In any case, I put 40 rounds through it without a bobble.

Tried two other things. Took a piece of old guitar string and made a ring; that didn't work. Apparently the spaces in the winding let too much leak out, or it just didn't fit tightly enough. The other thing was a piece of brass wire(steel would work as well). Made a ring that fit tightly, but the wire at .065 diameter was too big for the tube to fit on, so I cut it down with a dremel sanding drum so it's about the same diameter as the valve body, and tapering thinnner toward the tube. The tube goes on snugly, and it went through 40 rounds with no problems. Depending on the extent of a rifle's problem, you probably could, in some cases, just use a suitable diameter wire, in others you'd have to shape a piece to give the fit you need.
Or, if you want a new valve, VHC found this link to a guy who started making them when his rifles all gave him trouble.

This ends my current lecture on screwing around with an already functional rifle. Goodnight, VHC, wherever you are.

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