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Cracked Front Trunnion after AR Mag mod


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Vlad, thanks for the great information. So, I have a couple of clarification questions please.

 

1. If I have a Saiga .223/5.56, I for whatever reason, I wanted to replace the trunnion, the bulgarian AK-74 5.45 trunnion is a direct replacement. Question: Are there any OTHER trunnions that are a direct replacement, if I was looking for one?

 

2. If replacing the trunnion, being it contains the serial number, is considered a felony, what would be the proper procedure for replacing the trunnion on the saiga .223/5.56?

 

3. If I replace the trunnion on the saiga .223/5.56 with the bulgarian ak-47 5.45 trunnion, or one of the others you might say are also a direct replacement, and I have no intentions of selling the rifle, and I keep the original trunnion with the serial number on it as proof of the weapon's originality/ownership, is that still a felony?

 

Thanks Mike...

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If i may...

 

Vlad, thanks for the great information. So, I have a couple of clarification questions please.

 

1. If I have a Saiga .223/5.56, I for whatever reason, I wanted to replace the trunnion, the bulgarian AK-74 5.45 trunnion is a direct replacement. Question: Are there any OTHER trunnions that are a direct replacement, if I was looking for one?

 

All 22mm trunions should work as long as they are AK-74/AK100 series style. Bulgarian Ak74 and Polish Tantal are the first that spring to mind, A trunion from a Saiga 7.62x39, .223, or 5.45 would all also work. Not much else that springs to mind will.

 

2. If replacing the trunnion, being it contains the serial number, is considered a felony, what would be the proper procedure for replacing the trunnion on the saiga .223/5.56?

 

I don't know that it can be done, consult an 07 FFL (manufacturer) who deals with these rifles.

 

3. If I replace the trunnion on the saiga .223/5.56 with the bulgarian ak-47 5.45 trunnion, or one of the others you might say are also a direct replacement, and I have no intentions of selling the rifle, and I keep the original trunnion with the serial number on it as proof of the weapon's originality/ownership, is that still a felony?

 

Imagine that the serial number on your rifle is on a plaque riveted to your receiver. If you cut those rivets and remove that plaque with the serial number from the receiver- you have defaced the serial number by "removing it" from the receiver. Weather you altered or defaced the number stampings themselves is irrelevant- you have removed the identifiying marks from that receiver.

 

Now look at your front trunion. It is essentialy that, a place where your serial number is kept, attached to the receiver. You cannot seperate these two pieces- the trunion IS the serial number too- it can't come off. You can build a new rifle on a new receiver and trunion. Or your can try and 07 FFL who might be able to do things that you and I can't.

 

Thanks Mike...

Edited by JK-47
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JK, thanks for the response. But being someone who is quite knowledgeable of legal procedure; I'm not a lawyer, but the wife is, and I stayed at a Holiday Inn Express once; this brings up a very valid question:

 

If removing the trunnion, and replacing it is a felony, then why would it be legal to sell trunnions in the united states without having to go through an FFL licensed dealer??? Seems like that would be the deal. When the frame on one of my PA-63 9mm makarov pistols cracked, I ordered a new frame from an online distributor. It had to be shipped to my local FFL dealer. He in turn did the same paperwork as if it had been a new and complete pistol. i then went home, put on my old slide, springs, barrel, etc... and had my new gun. Seems like if the trunnion of the saiga, because it has the serial number on it, was the "FFL Legal Part of the Gun", then NO ONE would be able to sell that part to me without using an FFL dealer as an in between. You can't buy a gun, frame, etc... on gunbroker without going through a dealer. WHY then, can you buy a trunnion?

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Sorry, bout the rant, but you can't just replace the trunnion on the saiga with out completely destroying the reciever as per the alpha-bet boys specs.... and if you quietly replace it and no ones the wiser i guess that might work for you but if you sell the firearm and the buyer smellls something funny you're in a world of hurt, like unregisterred SBR world of hurt....

 

See the other confusing thing is, like for instance, some imported ak recievers have the serials stamped on the shell itself, so removing the trunnion off those rifles is absolutely not an issue. can't think of any impports off the top of my head, but say a century ak-74 with a NDS reciever.... at any time you can completely strip EVERY thing off the sheet metal on those rifles and even legaly sell the actual shell without hassle because only the shell is a reciever and the trunnion is just that, a trunnion....

 

unlike the saiga where the trunnion carries the serial number and is then automaticly an inseperable part of the receiver...

 

as far as other replacements go, any ak74 trunnion (22mm) will work from any country that made an ak74 to russian specs. Russian thrunnions, Bulgarian, east german, and I think thats it... unless i missed a couple, i can't think of any other country that made a proper ak74... poland had a 545 rifle but its diff and since i never had a polish tantal parts kit to take accurate measurements (i just kept buying the akms kits) i can't really say for sure if its a 22mm or 23mm trunnion...

 

the only issue u might run into is having to use whatever bullet guide you have currently as the bullet guides in the 556 and 545 22mm trunnions may by slighly different...

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the reason its legal to sell trunnions in the states is that in the states, the trunnion is not a regulated part of the receiver....

 

any surplus rifle built on a NDS or any other US made (or import for that matter) reciever with the original serial numbers stamped on the shell can be stripped down and transfered as just the shell.

 

whats throwing everybody here for a loop is this....

 

the saiga rifles have their serial number, the one thats registered as a rifle (or listed i guess, whatever) on the trunnion, not the shell.

 

parts kits have the original serial numbers still on the parts and it confusese people, but what every body needs to know is that these numbers are in no way a legaly binding serial number.

 

so for instance, i build a polish akms on a NDS shell, right? the only number of any legal significance on that rifle would be whatever is on the NDS shell... the other numbers that were already on the parts kit (and trunnion) can be de-faced at will, they are not the serial numbers, unlike the saiga rifles...

 

its confusing i know...

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its the sheet metal shell thats a regulated Item on ak rifles, the trunnion is absolutely not a regulated item.

 

it just cannot be removed from some rifles because IT carries the serial, again, this applies only to SOME rifles... and if the reciever shell becomes destroyed (cut up) then that number and trunnion are then free to roam the country as unregulated scrap metal for all anybody cares....

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Vladimir - It would appear that you have answered RLTW's question - at least regarding the compatability of and type of trunion that would be needed to replace his Siaga trunion. From what I have read above, from Red Jacket, we see a manufacturer's take on the matter. My words to RLTW were to mainly bring up possibilities and offer some dirrection in terms of obtaining answers or "facts". There indeed many quirks and specific issues regarding parts interchangeability. My own Siaga 7.62X30 that was converted to .223 utilizes Galil .223 mags - it does not have a bullet guide and it appears that the barrel itself might be a sleved Chinese barrel. Some nine or ten years ago when I was speaking with the manufacturer about building the rifle, he informed me that the barrel would be either Bulgarian or Chinese. I told him that I preferred Bulgarian. During the same time period I inquired to this specific builder if he could take a Siaga 7/62 X 39 barrel and build it onto a milled receiver, or stamped receiver - he informed me that he could do this, primarily by machining a sleve in the instances where the inside trunion diameters are larger than the breech end of the barrel. He did not elaborate on "profile" or parameters. He explained that he would build me essentially what I wanted. This was a builder who built AK rifles for both private and government use, and worked on other types as well. He did not have a high opinion of the MP-5, which has long been one of the "favored" firearms among law enforcement. He did re-build Siaga AK rifles by the dozens at a time and utilized electro powder coating much like the factory type of the time to finish. He also built many milled receiver rifles off of Polish Parts kits. He did favor the AK platform and was an enthusiast regarding the AK design and robust function. I also am an AK enthusiast - and I also own a wide variety of makes and calibers of them. I also look to see what can be done, not what can't be done in terms of AK re-builds and builds. Respectfully, and In Freedom, Hamerforged.

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:-) cool. Yeah, a lot can be done with a machine shop, custom fitting the parts pretty easy. was mainly refering to drop-in replacements and so forth.

 

thanks for the clarification, your build must've been a long long time ago for it to be worth sleaving a chinese 84s barrel to a trunnion and so forth...

 

nowadays just the chinese parts in question are worth twice a saiga 556... :lolol:

 

crazy times we live in.

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Thanks for all your help guys.

 

This past weekend I welded up the area, cleaned it up with the dremel. I am ordering a rivet set and when that comes in, I plan on putting things back together. So hopefully that will fix my little dilima.

 

Obviously, if that does'nt work...

 

Plan 2 is order a new flat, and AK 74 trunnion. And rebuild that route.

 

Thanks to everyone. :super:

 

btw. I just bought a Draco ... so that will be a new toy to play with along with all my other stuff. :eek:

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LOL, I just finished my AR magwell mod using a Dremel and looking to talk about it only to find this thread. Looking at your pictures, your trunion looks much better than mine after the mod. We'll see how mine goes. Before doing the mod, I had installed a Dinzag bullet guide for use with my Promags only to find that the bullet guide interferes with the AR mag adapter. So now I also have a threaded hole in the trunion as well that can't be used unless I mod the guide to fit with the mag adapter in. I'll just count my lucky stars in hopes that the trunioun doesn't fail on me anytime soon.

 

BTW, I also have a Draco as well, but its not as fun as the .223 because I have it set up as a "featureless" rifle so that I can have free dropping mags. The Draco is a b%t@h because I have to deal with the mag lock.(I'm in Kalifornia) So its not so fun shooting only 10rnds and then have to wrestle with the gun just to pop in another 10rnds.

 

However, the .223 with the AR mag adapter makes mag changes a snap. So eventhough I'm limited to 10rnds per mag, quick mag changes with AR mags will help solve that problem.

 

Keep us posted on the status of you .223

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  • 3 weeks later...

I had my trunnion crack after modifying for a mag adapter as well. I also shot around 800rds before trouble arose. Sadly I did not go the rebuild route since It was an unconverted saiga. I ended it up disposing of it at the local PD :cryss: . Worked good while it lasted but yea I'd stay away from modifying the trunnion from now on.

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Would be interested to know how the trunnion was milled. I have my ideas but would like to get some more info.

 

Looking at the metal, I believe the trunnion is cast and not milled. There is no doubt some milling after the fact, however cast metal tends to be crystalline and brittle, and fatigues quickly if overstressed.

 

The reason the trunnions are cracking is enough metal is being removed so that the trunnion is flexing where it is not meant to flex. Like bending a coat hanger repeatedly in the same place, the metal first fatigues, then crystallizes, and then simply comes apart at the point of least resistance and greatest stress.

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Waffen... Not what I meant. I meant what method used to remove the material. I am very aware of the manufacturing process. My theory is the metal is not properly removed more over I believe the process used has removed the tempering of the metal. I have my suspecions this is due to people not properly removing the materia... In short overheating. I have guns with 3000 plus rounds and no failure. The only constant is I machined with cutting bits. if you are dremeling your trunnion and you remove the temper then your prone to failure.... It's simple metal 101. I just want to establish the cause.

 

Call it a hunch... I just want to get to the bottom as I believe the obvious is being overlooked. There are trunnions out there with less material doesn't mean they are unsafe.

Edited by MSA
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if you are dremeling your trunnion and you remove the temper then your prone to failure....

 

Not sure you are on the right track. Metal density can vary widely from one casting to next. A denser casting is going to be more resistant to flexion and breakage.

 

You won't find a dremel anywhere near my shop, but even so just for the sake of argument, if one were to use a dremel or any other tool with a rotating head to remove metal - it isn't necessary to heat the metal to the point of affecting temper to remove what you need to remove.

 

My guess is that the wild card is the metal density and quality of the casting, which varies from gun to gun with every other cast part.

 

It stands to reason that the quality and density of the front trunnion casting will vary as well.

 

JMHO

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While the casting quality may be a factor... I just want to investigate the process. Heat being the byproduct of the dremel removal process is what I am thinking. If I can take a grinder and heat steel to the point of high heat then a dremel is capable of the same. Friction having heat as a byproduct.. Then it may be possible to remove tempering or expose casting issues with quality control. Like I stated just a theory I want to investigate.

 

I just know in my shop all tools that cut or remove material it is key to have cooling under control or you have big problems. Bits will break and these are not cheap steel castings... Specialty carbide bits.

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Couldn't the ADAPTOR be milled/relieved abit in THAT exact spot so users don't have to risk this??

 

Just asking I have no idea.. (don't own a 223 at this point).

 

Would like to get a S-223 if this matter gets resolved..

 

 

Albert

 

 

No, in my case, the only need for any milling/grinding is so the mag will fit in the gun. The adapter needs nothing to fit the gun, so, nothing can be done adapter wise to solve or prevent this that I can see.

Edited by renegadebuck
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if you are dremeling your trunnion and you remove the temper then your prone to failure....

 

Not sure you are on the right track. Metal density can vary widely from one casting to next. A denser casting is going to be more resistant to flexion and breakage.

 

You won't find a dremel anywhere near my shop, but even so just for the sake of argument, if one were to use a dremel or any other tool with a rotating head to remove metal - it isn't necessary to heat the metal to the point of affecting temper to remove what you need to remove.

 

My guess is that the wild card is the metal density and quality of the casting, which varies from gun to gun with every other cast part.

 

It stands to reason that the quality and density of the front trunnion casting will vary as well.

 

JMHO

 

 

I tend to agree with this line of reasoning. I have over 5k rounds fired out of one rifle and in excess of 3k rounds through another without a problem, not counting the others that are out there. So far, only 1 has a problem. While this is unacceptable, it must first be determined what the cause was before any conclusion is drawn. Unfortunately, I have no way of comparing the density of 2 or more trunnions.

We are not the first to make an adapter, and I have never heard of another incident like this. All of them require some metal removal as the AR mag will not fit in the rifle without it. I do hope someone finds the answer, but I don't really see it happening soon, as you would have to test many trunnions and we just don't have access to them.

 

Ok, Edited to add: I really need to make sure I read the entire thread as I see we have 2 problems. I wasn't extremely worried with one, but two? I wonder if both of these rifles were made about the same time. Both of mine are 07-08 vintage and have shown no ill effects.

Edited by renegadebuck
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The easy answer to determine the issue is to test the Rockwell of a new trunnion and one of that failed. If the Rockwell is out of spec. then you have a clear indication of the cause. Over heating and removing temper. It's simple science, the tools are there to determine cause and all we need is a subject to test and we can lay this to rest. To further drive the point, the same can be said for those who grind the hammer on the trigger group for conversion. There are reported failures of stress cracking after being modified, the only constant is overheating.

 

And to touch back on metal density and casting.... I'm not entirely convinced. If that was true we'd hear of trunnion failures all the time. Like ORF receivers mushrooming/cracking in the past due to being to soft and not properly tempered. I'd think we'd have a hell of a lot more failures than what is known. All over the forum people would be experiencing issues.... But that is not the case.

 

Lets look at what we do know... The first failure was installed with a dremel. Not faulting the installer but there is no way to know to what amount of heat was generated. The second failure I am waiting to hear of how it was installed.

 

Bottom line.... no metal working professional or gunsmith who stakes his income is going to use a dremel to remove material from a firearm. Sorry it is just known you have no absolute control over tolerances. MSA will always push to have it done professionally by a mill under proper conditions, yet we will respect the DIYer but do not approve this method due to to many variables. Until someone steps up with another failure and is willing to get the rockwel tested, then it will remain suspect number one.

Edited by MSA
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I was asked by a member recently, or at least he asked and I answered....what type of bit or tool should be used IF you are doing the install with a dremel. I answered a sanding drum, a small grinding stone, and a carbide cutter. I failed to mention however, something I just didn't even give any thought to since I have done so much sanding on wood and metals over time, it just is common sense to me....when ever you are using a rotary or belt sander on anything, you NEVER want to let your paper get worn down to the point where it's no longer removing material efficiently. You will do nothing but burn up your material or surface you are working on. Grinding wheels are different in that they are a certain coarseness and stay that way all the way til they are gone. Sandpaper wears fast though, and burns up. So I want to mention now that any time you use a dremel with sanding drum on metal, you need to use a slower speed and a coarser grit for doing a lot of metal removal. You should be seeing lots of metal dust and keeping a careful eye on the material, to make sure it does not get hot, and on the paper to make sure it doesn't lose all the grit and get worn to the core where it's doing nothing but creating friction and heat. Also you need to keep the thing moving, not just sit there in one spot an grind away til it's worn down and baking hot. Like a belt sander on a nice table top. You HAVE to keep it moving around and make no repeating motions or you wil cut deep grooves in the wood that you can't get out without sanding half the wood away. You can still see on my trunnion, scratches from where I removed the material. I never went back and finished it smoother because I'm still waiting for the final run of the adapters. I was fitting it using a plastic prototype at the time. The reason I mention the scratches is, if you are seeing scratches, you know you are using a coarse enough drum to remove metal without burning the shit out of it. Slow passes at a medium speed will do the trick. When you stop seeing metal dust you need to stop and check your sanding drum and change it if it's worn. You need to keep checking it anyway and stay on top of it's wear. You also have to keep it moving and actually feel the metal with your hands to make damn sure you don't overheat it. This is true for anything you are working on that's been tempered. If you see it turn blue then you just baked the shit out of it! Don't do that!

 

I am just putting these tips out there for you guys who are new to using these kind of tools or doing this kind of work. I have seen countless threads about guys going out and buying their first power tool, a dremel, and starting on converting their Saiga, lots of times it their first firearm as well. Without these simple instructions, unless you took shop class and metal working in school like I did, or had other training growing up, you probably never got exposed to these things. With as many new guys as there are converting Saigas, there are surely to be lots of first time DIY ers who don't have access to proper milling equipment or a machine shop, and are going to try this themselves with a dremel kit they picked up for 30 bucks at Home Depot.

 

I am NOT recommending that people use a dremel for this work, as Nate said, it's best to do it under controlled conditions with a milling machine. However, since lots will certainly be doing this with some form of rotary tool anyway, I wanted to be very clear that you need to do it right if using one, and not heat up the metal. I have read about people snapping their hammer in half (FCG hammer) because they overheated it and ruined the temper, and the steel became brittle enough to actually snap in two. These hammers and other FCG components are also cast steel, like your trunnion. Don't over heat it or wear it too thin, ruining it's integrity, and you will not have a problem with it cracking....that is...unless you got a Izhmash Lemon with a bad trunnion from the start, which may be what happened to these cracked ones we are talking about. ( I seriously doubt it though...)

 

I look forward to hearing an honest description from each of these guys, of how they removed material and did they pay close attention to the heating of the metal while doing so. If they got it hot, and weakened it, I hope they will realize it doesn't mean they are stupid, they just didn't know to watch it that close. If they used too fine a sanding drum trying to keep it smooth and pretty, then it's quite possible (almost certain) that they did in fact over heat the metal. If it's too hot to hold in your hands or touch your face against, then it's too hot and you are not using a coarse enough grit, or keeping it moving.

 

Sorry for the long, overly descriptive post. Some really need to hear it like that. All this said...I did mine with a dremel because it's all I had and Nate guaranteed me, since I was helping him develop his design, that he would replace my Saiga if I ruined it. I now have a milling machine and would never use a dremel for this application. It's fine for other work that's done by hand anyway and doesn't need to be exact and perfectly square to the thousandths, but when doing this kind of work a milling machine is best.

 

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Well after reading this thread i don't feel so good that mine won't crack on me now. I removed way too much from the trunnion. I also used a dremel as that's the only thing i have. I had some issues for awhile with getting the adaptor to fit properly and after emailing with renegade i got it to work now but i have not taken it out to the range as i have been busy as of late. I'm almost afraid to shoot it now as i'm almost confident it will happen to mine. Thanks for the info cobra.

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Cobra, thanks for your input for the first time DIYers out there.

 

The most important thing in the prevention of overheating and to ensure proper cutting is lubrication. Many people using a Dremel for the first time will just put a bit on the tool and hack at it dry. This is not only a poor way to cut metal but will also generate tool chattering and most importantly heat.

 

I had got the mag adapter about 6 months ago but didn't start on it because I wanted to research as much as possible on the method for how I would be able to do it with the resources/ tools I have. What I needed was a mill cutter that would fit my Dremel tool and I found it at the local Sears hardware department. Its a tool designed to cut metal like stainless steel sinks so I new it was tough enough to do the job I intended it for.

 

Also, many first time DIYers may have bought the "cordless" Dremel with the extra battery pack. Let me tell you that this kind of work will have you running out of charge in both packs waiting on your next cut while getting your batteries recharched. Definitely this is a job for a corded rotary tool.

 

When cutting with the tungsten carbide tool, I set it the rotary tool on the highest speed. Although I don't have any cutting fluid/ machine oil, I used my spray can of Rem Oil and sprayed the area to be machined liberally. I applied the Rem Oil with the start of every pass/ layer I would cut. As I applied the tool to the material, I made sure that I only applied enough pressure for the tungsten bit to do its job. I took a lot of patience, many passes and more than a half a spray can of Rem Oil but I was able to get it to fit.

 

I've test fired it with more than 200rnds so far and it has worked flawlessly. The mags I used were USGI metal mags but I was also able to borrow a C-products mag from someone at the range and it worked as well.

 

To the OP, I noticed that on the right side of the trunion where the crack was found on his gun, the cuts made to the trunion on the right side from the bottom create a sharp angle on the trunion where it meets the receiver. The crack that he experienced could have resulted from "crack propogation" stemming from the sharp angle in the trunion. This problem is normally avoided by cutting a radius into the angle such that it would prevent a crack from starting. So I radiused the sharp angle in the trunion where it meets the receiver. Hopefully this would help prevent the cracking in the trunion.

 

For those looking to do it on your own, here's what you need:

 


  1.  
  2. Corded rotary tool
  3. Tungsten carbide mill cutter bit
  4. Some kind of oil for lubrication
  5. A steady vise to hold your gun in place
  6. Digital calipers can be useful but not necessary because you'll be gauging the fit with the adapter and the mag.

 

Again, if you're unsure of this, it is better for you to find a professional who is willing and knowledgeable to do this work with proper machinery like a milling machine. I tried this before attempting to do it on my own but my local smith was not familiar with what was involved and wasn't willing to try. Hence why it took me 6 months to finally get it done on my own.

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Great DIY stuff...

 

Using the grinder.. should have been done in stages, just like welding ... slow and steady so you don't over Heat the metal. I know that is probably a factor.... along with over doing it.

 

Another, and this is What I consider the major factor, placement in the vise to do the work.

Looking back I put pressure on the outside of the receiver while doing the work, which could have caused stress on the trunnion as well as the heat from the grinding. Let it be known, vise/grinding was done over a period of 3-5 times... So by doing that over and over again I believe that is the main reason for the crack.

 

Anyways... I picked up a rivet set and in the next week I will be putting things back together after I welded up the trunnion.

 

I tell ya I still want to do the AR adapter once I buy another .223, but next time I will take it to my machineist and have them mill it out. All the way around it is cheaper in the long run, not to mention it will be done to spec, and it will look right.

 

Here is a pic of my Draco I just put together...

post-19827-087289000 1279492476_thumb.jpg

post-19827-020841000 1279492491_thumb.jpg

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  • 4 years later...

Hi of course if I am looking in on this I have gone and run into the same problem with the front trunnion on my Saiga 223 I would like to know if some one figured out what trunnion to use I wish I would of seen this before using the AR adapter. But I have what I have. Looking for a new front trunnion just not sure what trunnion to use.So if anyone out there that may have the answer for this problem I would grateful  to hear from you. Thanks Mike

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