A guide to AK mag a SKS and BHO mod.

[xtriggerman]

This is a most common question amongst SKS shooting enthusiasts. How can I get my SKS to use AK mags? The sensible answer to that is don't bother, or buy an AK, SKS M or D or get one of Marcus's various adapters that uses AR type mags.  Technically, there is a lot of modifying to be done to a standard SKS receiver to get a AK mag to run in the gun AND still maintain the strength & design integrity of the SKS action. A few years ago Shot Gun News ran a gun smithing article on how to do the conversion and in my opinion it was a total butcher job. First of all, the SKS being of tilting bolt design relies on the left and right rails of the receiver to support the bolt locking shoulder. Cutting away at them willy nilly so a AK mag can fit up in there is a good way to ruin your SKS. I don't even like the SKS D or M models that were factory SKS AK mag-ed for commercial sales. For one, they weakened the right side receiver rail by milling completely threw one area of the mag well "flat". Also, the SKS was designed to have a bolt hold open. This integral part of the design is a crucial component to keep it "mil Spec" duty. Deleting the BHO creates 2 mechanical shortcomings that was designed out of the AK. 1) the SKS firing pin, upon many dry firings can "volcano" the firing pin hole in the bolt face leading to blown primers from a cookie cutter effect. The AK Firing pin design is not prone to that miss fortune. 2) When the SKS bolt is free slammed on to an empty chamber (no bolt hold open function), the 9-12 o'clock position of the barrel chamber face will eventually be peened out into the chamber wall resulting in a inability to eject fired casings.  The ONLY thing that has kept my interest in this AK conversion is the idea that it can in fact be done without harming the structural integrity of the receiver design AND modify a standard steel AK magazine to function the SKS BHO just as the original 10 rd fixed box mag. The following information is NOT a solicitation for doing this for work! I am not in business. This is only one of my beloved hobbies. That said, paying some one to do this is more than likely way, way beyond what any one would want to spend on a SKS but hey, its still a free country just PLEASE, if you decide to do this on a SKS, do it on a bubba'ed up mis matched clunker of no collector value!
    The first consideration is to remove the most minimal amount of metal from the inner mag well to allow a steel AK mag to fit comfortably in it. In this pic, please know it is imperative you do not mill the radius area any deeper than it is in this pic. I go deep enough on it, just to take the blued finish off and no more. This is also critical to allow the AK mag to function the BHO. 
 
The leading edge of the radius is chucked up "level" in the mill vice so each pass replicates the original angled cut. The cutter used for this operation is a 9mm ball nose, 4 flute carbide end mill in a 10mm milling collet. All dimensions in this article relate to a Yugo SKS. The standard width of the SKS receiver is aprox 1.258". The mag well width needed to be achieved in this particular operation is 1.022 - 1.025" .  To achieve that, Aprox .025 needs to be milled away from the flat of the mag wall on both sides leaving a finished receiver wall thickness of .118". I set the mill bed stops to the original cut lengths so you simply move the bed over to the opposite side, keeping a mirror length cut of the opposite side as shown.
 


The next operation requires a 4 flute 1/4" square nose carbide end mill cutter.  Level the bottom flat of the receiver with the flat of the milling vice to mill parallel with the bottom flat of the receiver. Dye the original flats as pictured and measure 1.480 from the face of the receiver ring back to the flat and scribe a line on both sides of that distance. Zero the cutter off the dyed flat. There are 2 cuts to this operation. one is to maintain the prior cut wall thickness of .118 forward in the well and mill that dyed step down by .075 right up to the scribe line as pictured on both sides uniformly.


 Once this is done, There will be no more cutting of the receiver side wall. The next cut requires you to bring your cutter back up to your set zero of the dyed flat. This original dyed flat will be maintained with the milling to be done across the mouth of the opening as pictured. The depth of the cut foward could be anything from .035 to .050 as it varies in receivers. But as measuring as before from the face of the receiver ring to this new cut across, you should end up with .985" as pictured here. The width of the cut is only enough to make it across the opening of the well as pictured
 
In this next comparison shot, I have sharpie blacked out the original uncut flat. This high lights the last across cut and pictures the next 2 cuts above it to be made. The next being the same as last using the same 1/4" cutter to form a new "step" over the last across cut. Zero the cutter off the very top of the receiver flat (actual bottom) and bring the mill down .180 and mill across as before. Bring that cut forward toward the ring until you have .940 as the finished distance measuring as before from the face of the receiver ring back to the front wall of this new cut. The final cut here is the use of a 1/4" ball nose carbide 4 flute end mill cutter.  Zero the cutter on the top flat and make this cut .140 deep and .100 forward toward the ring and the finished cut will be centered in the receiver as a .320 wide cut.
 
  If every thing went as directed, you should have a mag well capable of fitting most steel AK mag dimensions....

At this point, the AK magazine latching hook should be aprox .050 rising up above the receiver flat as in the above pic.




Behold.... how the right rail is not milled threw with the high point of the magazine feed lip showing.
 
 The next segment of the conversion requires a steel latching step be fabricated and welded over then newly machined latching notch. I use a 110v mig welder for this purpose since it puts very little heat in the receiver. That's a good thing for not disturbing the heat treat hardness but will require an oven re-heat treat at about 375F to relieve some of the stress in the weld joint its self. If not done, the new latching piece could just snap off the receiver at some point with rough use. In my first conversion I simply drilled & taped 2 holes at the latch flat and screwed a latch plate on there and that was more than adequate so you really have a choice here. The next few shots are the making of said latch plate. 2 of them side by side. The  relief mill cut is .055 deep.
 
Once the new piece is in a clamped position, take the largest length wise AK mag you have and rock it in and out from under the plate. This will force the plate forward to a position that allows the insertion and removal. Be for warned, AK mags vary greatly in this spec of from under the latch hook to the rear of the mag at the very top of the lock in plate. My widest mag runs 2.515" and I have one at 2.478" So be prepared to mill the leading edge of the welded on plate forward a tad if you run into mags that wont rock into place or you can trim the back edges of the mag. Your choice.



 The only way this minimally invasive machine work will work out as a reliable feeder is you will have to cut 2 new feed ramps into your chamber face at the 5 and 7 O'clock position. I have never had a single hick up with this feeding or ejecting. As a matter of fact, the pictured feed ramps will feed the big blunt round lead soft points that I don't remember who makes flawlessly.

   In the next segment, I will describe in detail the AK mag mods needed to function the SKS BHO. 
OK, The AK magazine works well for its intended purpose due to its robust design and that entails a very strong follower spring and a follower that can slop on past whatever may fall into the hull. Its these 2 features in particular that allow for a follower and hull modification that will reliably function a modified SKS bolt hold open device.
 First off, The SKS receiver to be used in this conversion can not be a D or M model since neither was machined with the traditional BHO devise. There is only one receiver mod that must be done to the receiver its self. That is to mill down the BHO spring hole wall. I use a 1/8th diameter carbide end mill cutter for this operation. With the receiver chucked belly up flat in the milling vise, set the cutter to zero at the top edge of the wall that separates the spring hole from the mag well its self. Mill this thin wall down by .060" and clean up the cut so as to have the Bolt Hold Open piece slides up toward the bolt by the additional; .060" of travel. It must slide up and down smoothly so any fine edges in the new cut needs to be cleaned out with a dremil and the little spring nub on the back of the hold open can be trimmed a tad for smooth function. The spring need not be cut.

The next step is to mod the BHO piece its self. Mill .060 off the very top and .060 off the very bottom of the little hook. This gives a over all new height of .675 and a hook height of .170".

The bottom edge must be beveled off as in this pic.

The next step is to mill away the follower where it stops on the hull follower nubs. I milled .175" down from the top flat of the follower. Find this area by scribing around the hull stop nub with the follower pressing up against it as in a empty unloaded mag. The intension here is to make the feed lip be the follower stop rather than those 2 nubs in the hull body.
 

Next you need to find a thin leaf of spring as pictured. The spring I used was about .015 thick and I trimmed it to a length of 1.550 and a width of .315". Its welded position allows the top of the spring to protrude .180 above the top of the follower bed.


  A small relief is cut at the top follower flat where the spring will touch when pushed all the way forward to touch the follower bed. The depth of that cut is to allow the spring to be flush with the top back edge of the follower.
This picture captures that thin relief cut and what the final job will look like compared.

The back of the hull must be milled as pictured. The top protruding edge is milled down ward by .110".

 
The next mod is to mill a relief of the inside of the magazine as pictured. The mag is set up in the mill vise with the feed lips set at a 70 degree angle from the top of the vice flat.

Bring the cut down so it will make a blunt edge at the top of the last operational cut. This cut will allow the slight bend in the spring to get under the BHO as the last cartridge leaves the magazine.



 Spits em out & locks open like factory!

[gjohnsoniv]

I think that you just killed the myth about "it's easy to convert an sks to take an ak mag."

[xtriggerman]

51 minutes ago, gjohnsoniv said:

I think that you just killed the myth about "it's easy to convert an sks to take an ak mag."

On the contrary, Folks following directions of one article on the subject still believe its easy peasy simply because to quote the article, " Remove feed rails and widen frame to accept magazines".  Hows that for cutting bubba loose with a dremil & grind stone.  Lesson here is NEVER EVER buy a SKS that has been home modified for AK mags unless you take it apart and actually see the recoil shoulder is still attached to the receiver ring with most of the mag well metal.  It pains me to think about how many good SKS receivers have been ground into a potential face grenade because of these old DIY instructions over the years.  Like the old saying, Why study & learn when ignorance is instantaneous!   

[OLDNEWBIE]

Good info!

I finally acquired an SKS about a year ago on a trade.

As with most SKS owners I pondered what it would take to make it take AK mags. Even though I prefer the fixed mag design. That's one of the unique features that made it desirable to me in the first place.

Although it's not something I would ever do, I appreciate why people go this route. It's a bit of a skill challenge and...

Because they can.

[peejman]

Tagged for more in depth reading when I have more time. 

[Capbyrd]

Wow.   Great read. 

 

[Reiko747]

How much would you charge to do my Sks ?

[Cumberland]

That is a cool ptoject. Very creative.

[xtriggerman]

Sorry, I have waaay too many irons in the fire to bang out a AK mag machining job. That said, any "gun guy" machinist can do it. Just give em a copy of the instructions and see what they say.