How to add an AR stock to a Zastava M77

Okay, some guys hate AR gear on AKs and if it’s not your cup of tea, that’s fine. I do like AR stocks and have no problems putting whatever stock on whatever family of firearms. I’m more into pragmatism and making a firearms do what I want than arguing over AR vs. AK or whatever. This is also why I have commenting turned off on the blog.

At any rate, even before I bought the M77, I knew I was going to trick it out for my purposes and I wanted to put one of the Magpul PRS Lite stocks on it for a few reasons:

  • I like adjustable stocks like the PRS but don’t need to constantly change the length of pull or the comb (where your cheek sets) thus I didn’t need to spend the money on a full blown PRS Gen 3. By the way, in case you are wondering PRS stands for “Precision Rifle/Sniper”.
  • The M77 will never be mistaken for a carbine given its length nor do I need to collapse the stock so the fixed postion PRS Lite was fine by me.
  • There are aftermarket thick recoil pads you can put on a PRS to absorb recoil.
  • By using a buffer tube, I can slide in a mercury recoil suppressor to add weight, absorb some of the recoil and balance the rifle out a bit more to compensate for a long barrel and relatively heavy front end.
  • Last but not least, the PRS Lite reminds me a bit of a PKM stock due to the skeletonized opening. (I’m sure someone just spit their drink out reading that). I had a new mint Romanian PKM stock many years ago that I sold at some point and still wish I hadn’t. In short, I like the looks.
  • Also, the PRS Lite is a bit cheaper than a PRS Gen 3 but that wasn’t a big factor for me – the PKM look is actually what tipped me in the direction of the Lite model.
This is the MagPul PRS Lite. It’s definitely a solid stock that I like – it does what I need it to.

Parts you will need

  • Zastava/Yugo to M4 adapter – this screws into the square hole in the rear trunnion and then presents the hole the buffer tube screws into and the end plate. Go with an aluminum model from a reputable vendor like Ace, JMac Customs, Desert Fox, etc. Note, JMac went a very different route with their pioneering 1913 Picatinny rail interface for the stocks and I provide more details down during installation.
  • A buffer tube – I’d recommend a M4 six position Mil-Spec carbine buffer tube for the greatest flexibility. Rifle length tubes are rarely used on new firearms now as people want the adjustable stocks. Commercial sized buffer tubes were due to some things Colt did many years ago and thus on the way out so go with Mil-Spec which refers to the outer diameter of the tube.
  • An AR end plate – on an AR, this plate keeps the selector spring captured and also aligns the buffer tube via vertical key that sticks up and keeps the carbine buffer tube from rotating – it does help to have it for that reason and you have tons of options out there ranging from the basic to ones with sling hooks and even QD sling sockets. Not all adapter support an end plate so this might not be needed,
  • A castle nut – this nut is threaded on the buffer tube and then tightened down against the end plate to secure the buffer tube in place. Note, you will need a spanner wrench or specialized castle nut wrench of install or remove a castle nut without tearing it up – I recommend the Magpul wrench. By the way, the castle nut gets its name from looking like a medevial castle’s crennelated tower. Crenels are the parts that stick up like teeth to give defenders some protection.
  • Finally, whatever stock you want. Just remember to match the buffer tube to the stock. If you get a rifle stock and it needs a rifle buffer tube then get a rifle buffer tube, etc. The PRS and PRS lite have an adapter and can work with either tube type but most stocks designed for a carbine can only work with a carbine buffer tube (just make sure you match on either the Mil-Spec or commercial diameter).

Removing the old stock

The first step is to remove the recoil pad which is held in place by two beefy wood screws with allen/hex wrench sockets in them. Remove them and then the recoil pad will pull off. You then remove the buttstock bolt and the stock pulls out of the end of the rifle.

Remove these two beefy screws and the recoil pad will pull off. I’m happy to see a modern screw head vs. slotted. I would have been even happier if they were torx screws this is a nice upgrade from the old days.
I kind of felt like Crocodile Dundee when I first saw the new recoil pad screws they are using “Now this is a screw”. If you’ve not seen the movie then the reference is lost but my point is that is a really heavy duty screw.
With the recoil pad off, use a 13mm socket on an extension to reach in and unscrew the buttstock bolt. Yes, that’s a bed. It was super cold out and I set up in our spare bedroom to take these photos.
They’ve shortened the buttstock bolt considerably. I’ve considered having these made but Zastava USA seems to keep them in stock so there is no pressing demand for them unlike our original Yugo military length bolts.
This is what goes into the rear trunnion. The numbering reflects the rifle it was fitted to. Note, these do sometimes get a wee bit stuck in the trunnion so you might need to wiggle it a bit or a few light taps with a rubber mallet and it will pull right out.
This is the rear trunnion and the use of a square hole and big bolt to secure it is one of the unique design changes the Yugoslavs did to the Soviet designs. See the finish residue and chips in there? The snug fitting of the stock, how much the finish has stuck to the metal and a bit of sawdust all combine to cause the stock to offer a bit of resistance during removal. In this case it all came out easily with just a bit of wiggling. You should remove all of that of course.

Adding the new stock

To add the buffer tube, I decided to use two parts that I happened to have in stock. I used an Ace modular adapter (“AKRBY-AR15” is the exact model) and then a JMAC modular stock to M4 adapter that has sadly been discontinued – I bought mine a few years ago so it’s not surprising things have changed.

JMac went a different route some years back and pioneered adapters that expose a 1913 Picatinny rail at the rear to which you can mount a ton of different stocks. That’s another option for you – click here. Once you have that, you add a folding mechanism, then a skeletonized tube (ST) for a cool “I’m not a normal AR look” and then your AR stock if you go that route.

Many, many years ago, Ace Riflestocks was its own company and alos quite a few years back they were acquired by Doublestar Corp – a large AR manufacturer. Same products and quality but you now see a Doublestar logo. Note, there is an Ace to M4 adapter that I have used many times but does not support the end plate. Not the end of the world but a different approach.

If you do not want the modular approach, Zastava also sells a direct adapter. It screws into the rear trunnion and gives you the mount for the M4 buffer tube.

This is the Ace Zastava/Yugo modular stock adapter. Only one of the two rows of screws holes are actually used giving you a bit of vertical adjustment. The adapter is secured by an 8mm allen key socket screw. The screw holes are tapped for #10-32 screws.
The JMac M4-Ace adapter is really well made. The two horizontal screw holes are for securing the Mac Adapter to the modular stock adapter. The bottom opening is for securing the botttom of the AR end plate that in turn holds the buffer tube in position vertically.
Put medium strength Loc-tite on before you install the screws.

If you want to insert a mercury recoil reducer

This next step is entirely optional – I installed a C&H mercury reducer to add weight to the rear and absorb a bit of recoil. The completely sealed 7/8″x5″ C&H tube weighs 16oz. The liquid mercury inside sloshes inside and absorbs some of the recoil. Does it do a ton on it’s own – no. Does it and the weight help mitigate some of the recoil? The short answer is yes.

What I do is wrap tape around the C&H so it fits snug and is roughly centered. I spray brake cleaner in the tub to get any oil out. scuff it up and spray it out again. I then scuff up the C&H tube, clean it with alchol (brake cleaner makes the tape gooey), coat the C&B unit with epoxy and push it in. Some epoxy will come out the drain hole so wipe it off with a rag with brake cleaner and then close it with a piece of tape. By the way, one end of the tube is tapped for a 1/4-20 bolt to help install it. Remove the bolt before everything sets up of course.
That’s not coming out or loosen up. Use a towel with brake cleaner to remove any epoxy on surfaces you don’t want. You need to do this before it sets up. By the way, the longer an epoxy takes to cure, the better it will hold up to shocks over time. Don’t use epoxies that claim to set in just 90 seconds or 5 minutes.

Let’s continue with installing the buffer tube

Put the castle nut on the buffer tubes with the largest slots facing backwards and thread it all the way to the bak, Then install the end plate with the “boss” (raised oval) facing forwards to it will go into the end of the AR adapter. You then insert the buffer tube into the adapter and start screwing it in place. When you can’t screw it in any further because of the plate, back it off a turn, push the plate into the adapter, tighten the castle nut with your fingers. Finally, tighten it down with the caste nut wrench – the torque spec is 38-39 ft pounds (you’ll sometimes ready 40 ft pounds but 38-39 is per USMC TM 05538/10012-IN). If you want to do farmer tight, that is up to you. I’d also recommend staking the nut – putting a divot in the nut in one of the small holes between the end nut and the castle nut so the castle nut can no longer turn without a wrench. Again, up to you.

Here you can see the end plate, the groove in the buffer tube that it travels in and just a bit of the castle nut behind. All are oriented correctly.
I screwed in the buffer tube until the end plate couldn’t rotate, backed it off one turn (or so) until I could get the end plate to slide forward and go in its hole. Note the orientation of the castle nut and it is not tight yet.,
Do you mess with castle nuts a lot? Get a Magpul Armorer’s Wrench. In the photo, the right side is for the castle nut. The left is for the barrel nuts and I don’t use that one much but that castle nut portion gives you a wonderfully secure grip especially when you are breaking ones free. The square hole is for a 1/2″ torque wrench. The oval hole is for rifle receiver extensions and the groove in the castle nut end can be used on the traditional bird cage flash hiders.
Once the buffer is installed, the PRS site can go right on. Just follow the directions with the stock, You remove the screw that holds the front flush cup in place and slide the stock on. You can then put the QD swivel flush cup on whatever side you want.
Both the full blow PRS Gen 3 and PRS Lite stocks have thin hard recoil pads that I always replace. This is a Limbsaver PRS Gen 3 recoil pad that fits both models. It’s well made, fits and feels great. I always make the swap unless the stock is going on a light recoiling rifle like 5.56 NATO. If you want the best recoil pad I have found for the PRS Gen 3 or PRS Lite, get the Limbsaver pad.

End Result

The rifle feels really good and handles well. I think it looks great also!


Once you know the parts you need, it’s a pretty easy swap to make. Once you get the M4 buffer tube installed you have tons and tons of options out there .

I hope this helps you out.

Note, I have to buy all of my parts – nothing here was paid for by sponsors, etc. I do make a small amount if you click on an ad and buy something but that is it. You’re getting my real opinion on stuff.

If you find this post useful, please share the link on Facebook, with your friends, etc. Your support is much appreciated and if you have any feedback, please email me at in**@ro*********.com. Please note that for links to other websites, I may be paid via an affiliate program such as Avantlink, Impact, Amazon and eBay.