Re: Building a Yugo M72
27Yeah, I love AKs. Nice job!
It is an unfortunate human failing that a full pocketbook often groans more loudly than an empty stomach.
- Franklin D. Roosevelt
- Franklin D. Roosevelt
Re: Building a Yugo M72
28i don't care about AKs, i'm just enjoying the process.
i'm retired. what's your excuse?
Re: Building a Yugo M72
29Wow. Never imagined I would hear that from someone.
People usually have opinions about AKs.
It is an unfortunate human failing that a full pocketbook often groans more loudly than an empty stomach.
- Franklin D. Roosevelt
- Franklin D. Roosevelt
Re: Building a Yugo M72
30 i'm a battle rifle guy, this whole assault rifle thing is just a passing fad.
i'm retired. what's your excuse?
Re: Building a Yugo M72
31With the barrel stubs all depopulated it's time to move back to the receiver and it's dreaded rivets. I did a bit of cleanup on the front trunnion, mainly grinding off some of the leftover spot welds and the outside bits of the long rivet that goes in the bottom front of the trunnion. It still has work and I'm trying to be careful there so no real progress.
Where I haven't worked yet though is the rear section of the receiver. This has the stock, rear trunnion, sling mount and the bits that surround the trigger riveted on, with a really inconvenient chunk taken out where the fire control holes were drilled (I believe this is because those holes were drilled for full auto). The rear trunnion is attached to the remains of the receiver with more of those annoying long rivets on the sides, as well as a short rivet on the bottom (I think this might be unique to RPKs or maybe just to yugo AK pattern rifles). The trigger guard and mag release is held on with 4 short rivets on the front and the rear has two more short rivets. The sling mount is just held on with a piece of sheet metal that is folded through a slot.
Where I haven't worked yet though is the rear section of the receiver. This has the stock, rear trunnion, sling mount and the bits that surround the trigger riveted on, with a really inconvenient chunk taken out where the fire control holes were drilled (I believe this is because those holes were drilled for full auto). The rear trunnion is attached to the remains of the receiver with more of those annoying long rivets on the sides, as well as a short rivet on the bottom (I think this might be unique to RPKs or maybe just to yugo AK pattern rifles). The trigger guard and mag release is held on with 4 short rivets on the front and the rear has two more short rivets. The sling mount is just held on with a piece of sheet metal that is folded through a slot.
Re: Building a Yugo M72
32Someday I will have a 6 ton press and all the fixtures to make AK's.
I would love to build an M77 .308. Zastava SWEARS they are going to import those again. Someday. Getting a parts kit may be easier.
I would love to build an M77 .308. Zastava SWEARS they are going to import those again. Someday. Getting a parts kit may be easier.
In a bacon, egg and cheese sandwich the chicken and cow are involved while the pig is committed.
Re: Building a Yugo M72
33If we knew then what we know now.... I would have bought one. I assumed they would be around forever.ErikO wrote: Wed Aug 21, 2019 10:48 pm Someday I will have a 6 ton press and all the fixtures to make AK's.
I would love to build an M77 .308. Zastava SWEARS they are going to import those again. Someday. Getting a parts kit may be easier.
It is an unfortunate human failing that a full pocketbook often groans more loudly than an empty stomach.
- Franklin D. Roosevelt
- Franklin D. Roosevelt
Re: Building a Yugo M72
34Removing the sling mount was easy, just take some small pliers and straighten out the tabs that hold it in then slide it out through the slot. I wish everything about demilling this was this simple.
Getting the rear trunnion out from the receiver is the same as it is for the front trunnion. Flatten the rivets, center punch them (hopefully in the center), drill deeper than the face of the receiver then grind the rivet flat. Then stick the receiver in a vice and pull it off. The same extra spot welds that were on the front trunnion were also present here which makes pulling this thing apart that much harder. But it got done.
Getting the rear trunnion out from the receiver is the same as it is for the front trunnion. Flatten the rivets, center punch them (hopefully in the center), drill deeper than the face of the receiver then grind the rivet flat. Then stick the receiver in a vice and pull it off. The same extra spot welds that were on the front trunnion were also present here which makes pulling this thing apart that much harder. But it got done.
Re: Building a Yugo M72
35i see sarco is selling demilled bren parts sets...
i'm retired. what's your excuse?
Re: Building a Yugo M72
36That would be cool but way beyond my skills and toolset. You have to reweld together the torched receiver and modify the gun to fire from a closed bolt.
Re: Building a Yugo M72
37I've been away from this project for a bit due to vacation, and also some frustration with some demilling.
A few weeks ago I was trying to get the rivets out of the rear trunnion, and I failed miserably. One of the issues with eyeballing the center of a rivet is if you try and drill the rivet from both sides you run the risk of missaligning the drill holes, then you end up with a fun disaster like I had where I broke a cobalt drill bit off inside of my rear trunnion. Not even broke off like "Oh just grab it with a pair of pliers and twist it out" either, full on broken off with nothing exposed. I tried some different ideals on how to get it out, including pounding with a hammer, drilling it with a better drill bit (end result, another broken drill bit). In the end I just gave up and bid on a new rear trunnion from gunbroker. I also invested in this tool from ak-builder to help you drill in the center of the rivet: https://ak-builder.com/index.php?dispat ... t_id=30649
Took the new tool, drilled through one side of the new rear trunnion's rivet heads, ground them off and then tried a different technique of pounding the partially drilled rivet out with a punch. This technique worked much better than my old one.
Once I did the bottom rivets the rear trunnion came out nice and easy (this trunnion wasn't spot welded anywhere near as solid as the old one).
A few weeks ago I was trying to get the rivets out of the rear trunnion, and I failed miserably. One of the issues with eyeballing the center of a rivet is if you try and drill the rivet from both sides you run the risk of missaligning the drill holes, then you end up with a fun disaster like I had where I broke a cobalt drill bit off inside of my rear trunnion. Not even broke off like "Oh just grab it with a pair of pliers and twist it out" either, full on broken off with nothing exposed. I tried some different ideals on how to get it out, including pounding with a hammer, drilling it with a better drill bit (end result, another broken drill bit). In the end I just gave up and bid on a new rear trunnion from gunbroker. I also invested in this tool from ak-builder to help you drill in the center of the rivet: https://ak-builder.com/index.php?dispat ... t_id=30649
Took the new tool, drilled through one side of the new rear trunnion's rivet heads, ground them off and then tried a different technique of pounding the partially drilled rivet out with a punch. This technique worked much better than my old one.
Once I did the bottom rivets the rear trunnion came out nice and easy (this trunnion wasn't spot welded anywhere near as solid as the old one).
Re: Building a Yugo M72
38The last major bit of demilling was taking off the buttstock. This was simple enough, just take off the recoil pad and loosen the bolt that held the stock to the old trunnion.
Once I undid that a couple good smacks with a hammer and some levering with a screwdriver and the old trunnion popped off.
That basically concludes the demilling process! The only thing left is to drill out the remains of a long rivet in the front trunnion that refused to budge.
Lessons learned so far:
Once I undid that a couple good smacks with a hammer and some levering with a screwdriver and the old trunnion popped off.
That basically concludes the demilling process! The only thing left is to drill out the remains of a long rivet in the front trunnion that refused to budge.
Lessons learned so far:
- If you're demilling a receiver buy the damn AK-Builder rivet tool, it makes everything super simple.
- Have extra drill bits.
- Get a 1/2" Brass Punch and a 3# hammer for depopulating the barrel
Re: Building a Yugo M72
39It's been a bit and there hasn't been much progress on the M72 project. The next big stage is completing the receiver.
A lot of people seem to go with the cheap route for the 80% receiver and buy a flat blank thats been pre-drilled. This requires you to press it into shape, weld on the rails and center support and heat treat it. Thats a lot of work and requires tools I don't have space for. Childer's Guns sells pre-bent, welded and heat treated receiver blanks. These are more like AR-15 80% blanks that need drilling. In this case the holes for the fire control group and selector lever. These are heat treated so drilling the holes should be a great time.
I had this engraved with the yugo lettering for safe, semi and auto, and took it to my local engraver to put the serial from the torched receiver on the new one.
Right Side On the left side I had childer's engrave the Zastava logo, which it turns out isn't right for this year of M72 but whatever.
Left Side You can see the insides here. The rails and center support are all preinstalled and welded in. Less work for me.
A lot of people seem to go with the cheap route for the 80% receiver and buy a flat blank thats been pre-drilled. This requires you to press it into shape, weld on the rails and center support and heat treat it. Thats a lot of work and requires tools I don't have space for. Childer's Guns sells pre-bent, welded and heat treated receiver blanks. These are more like AR-15 80% blanks that need drilling. In this case the holes for the fire control group and selector lever. These are heat treated so drilling the holes should be a great time.
I had this engraved with the yugo lettering for safe, semi and auto, and took it to my local engraver to put the serial from the torched receiver on the new one.
Right Side On the left side I had childer's engrave the Zastava logo, which it turns out isn't right for this year of M72 but whatever.
Left Side You can see the insides here. The rails and center support are all preinstalled and welded in. Less work for me.
Re: Building a Yugo M72
40At first when I got the receiver blank I thought those nice dimples were where you were going to have to drill the holes. But the location didn't really make sense. It didn't take long to realize that those were the dimples from welding the rails onto the inside of the receiver. Childers to the rescue with a convenient plastic layout guide:
This also comes with holes for the front and rear trunnions but i had those pre-drilled (it actually lacks the M72 front trunnion holes that are on the bulge of the receiver, but those were pre-drilled as well).
The idea here is you line up the guide with the front and top of the receiver, clamp it down, then use a 1/4" transfer punch to mark the center of the hole you need to drill.
I did the center marking (and took pictures) but then I managed to screw up the end cap on my form 1 suppressor by not getting a hole perfectly aligned, which quickly made a fancy titanium cap into a fancy piece of trash. The plastic layout guide isn't meant to be used to guide a drill, but the Form1 forum I frequent gave me an idea and I ordered a set of 1/4" drill bushings. These press nicely into the guide holes and should do a much better job of keeping my drill centered where its supposed to be.
This also comes with holes for the front and rear trunnions but i had those pre-drilled (it actually lacks the M72 front trunnion holes that are on the bulge of the receiver, but those were pre-drilled as well).
The idea here is you line up the guide with the front and top of the receiver, clamp it down, then use a 1/4" transfer punch to mark the center of the hole you need to drill.
I did the center marking (and took pictures) but then I managed to screw up the end cap on my form 1 suppressor by not getting a hole perfectly aligned, which quickly made a fancy titanium cap into a fancy piece of trash. The plastic layout guide isn't meant to be used to guide a drill, but the Form1 forum I frequent gave me an idea and I ordered a set of 1/4" drill bushings. These press nicely into the guide holes and should do a much better job of keeping my drill centered where its supposed to be.
Re: Building a Yugo M72
41With all that work, is it fun? Worth it?
It is an unfortunate human failing that a full pocketbook often groans more loudly than an empty stomach.
- Franklin D. Roosevelt
- Franklin D. Roosevelt
Re: Building a Yugo M72
42I enjoy having projects to do, even if they end up costing more than I thought they would like this one. I do wonder if I would do this again, probably not for another RPK, but given what I've learned I might do another 80% yugo AK depending on how difficult populating the barrel turns out.
Re: Building a Yugo M72
43Very cool attitude! I hope these things aren't banned.
It is an unfortunate human failing that a full pocketbook often groans more loudly than an empty stomach.
- Franklin D. Roosevelt
- Franklin D. Roosevelt
Re: Building a Yugo M72
44Well now its officially a gun I guess!
Drilled the 1/8" pilot holes for the FCG, hammer and selector. The idea of using the drill bushings worked great and all the holes feel lined up when I put a 3/32" bit through them.
Still need to open up the holes to their final sizes, which depends based what the hole is for. Still researching exactly what sizes things should be.
Edit:
Some quick digging found the hole sizes needed:
Ejector Side Drill Sizes
Selector - 5mm (Pre-Drill with 4mm)
Trigger - 7mm (Pre-Drill with 4mm)
Hammer – 7mm (Pre-Drill with 4mm)
Center Support – 4mm
Operator Side Drill Sizes
Selector – 10mm (Pre-Drill with 4mm)
Selector Slot – 7/32” (Pre-Drill with 4mm)
Trigger - 5mm (Pre-Drill with 4mm)
Hammer - 5mm (Pre-Drill with 4mm)
Center Support – 4mm
On the Operator side, the selector slot is finished by removing material between the 10mm Selector hole, and the 7/32” selector slot hole for a final "keyhole" shape.
Drilled the 1/8" pilot holes for the FCG, hammer and selector. The idea of using the drill bushings worked great and all the holes feel lined up when I put a 3/32" bit through them.
Still need to open up the holes to their final sizes, which depends based what the hole is for. Still researching exactly what sizes things should be.
Edit:
Some quick digging found the hole sizes needed:
Ejector Side Drill Sizes
Selector - 5mm (Pre-Drill with 4mm)
Trigger - 7mm (Pre-Drill with 4mm)
Hammer – 7mm (Pre-Drill with 4mm)
Center Support – 4mm
Operator Side Drill Sizes
Selector – 10mm (Pre-Drill with 4mm)
Selector Slot – 7/32” (Pre-Drill with 4mm)
Trigger - 5mm (Pre-Drill with 4mm)
Hammer - 5mm (Pre-Drill with 4mm)
Center Support – 4mm
On the Operator side, the selector slot is finished by removing material between the 10mm Selector hole, and the 7/32” selector slot hole for a final "keyhole" shape.
Re: Building a Yugo M72
45that's pretty wood in post #38, pic 2. can you re-use it?
i'm retired. what's your excuse?
Re: Building a Yugo M72
46Yeah. The only parts right now I'm not planning on reusing are the FCG group and the pistol grip, I'm pretty sure that will keep me in 922r compliance.
Re: Building a Yugo M72
47922r only really comes into play when a Licensed Dealer sells a firearm. Also, your receiver is American so you are 100% compliant already.
In a bacon, egg and cheese sandwich the chicken and cow are involved while the pig is committed.
Re: Building a Yugo M72
48I’m really enjoying watching this. Thank you for the detail and the pictures. Also appreciate your attitude about enjoying projects. I started to go down the road of an 80% lower but I’ve never finalize that decision. One of the reasons is because I recall that I struggled to add a simple dust cover scope rail on a Yugo M92. I haven’t had a problem drilling rear trunnions to add folding stock adapters for example. But when I went to drill that dust cover I managed to put one of the holes where a weld was (That was some hard steel), and then ended up breaking a tap off in the hole that I drilled. I just ground it flat on the inside and left it as the rail covers it from the outside but it drives me crazy knowing it’s there. Between that and a similarly stupid Mosin T53 sight mod project that I attempted, the wind has been taken out of my DIY sails...offensivename wrote:I enjoy having projects to do, even if they end up costing more than I thought they would like this one. I do wonder if I would do this again, probably not for another RPK, but given what I've learned I might do another 80% yugo AK depending on how difficult populating the barrel turns out.
I’m vicariously enjoying yours though.
Re: Building a Yugo M72
49I finished up my form 1 suppressor last week so this is back to being my only project. I went ahead and drilled out the operator side of the receiver to get the holes to their proper size. I still need to cut the metal between the selector hole and the other part of the selector (the big hole to the smaller hole directly forward of it). This is where the selector lever slides in.