I had a fellow who was new to AK-47s/AKMs ask me the other day how the two pins work and if there was a published specification for them because his were floating in their holes. I learned a long time ago to try and help guys learn so I took a few photos and sent them to him.
Two Pins for Semi-Auto AKs
In a fully automatic AK, there are three pins and they are referred to collectively as the fire control group (FCG) pins – this includes the hammer pin, trigger pin, and sear pin – once in a while you’ll see the word “axis” thrown in there somewhere. For most civilians, we’ll just see semi-auto AKs so there are just two pins – one for the hammer and one for the trigger assembly which is made up of the trigger and disconnector. They are still called the FCG pins.
For anyone that is interested, a 1968 Soviet era armorer’s manual does have the pin specification:
This is from a Soviet era Armorer’s Guide that specs out the AKM fire control group pin. The shaft is 5mm and is where the trigger and hammer rotate. The same type of pin is used for both the trigger and the hammer – they are not unique.Here is a pile of pins from a mix of countries. I had them in one of my parts boxes. The diameters of the shafts vary from 4.921 to 4.988mm according to my micrometer. Based on the armorer diagram above, a diameter under 4.97 or over 5.03mm is out of spec. Three of those pins were under 4.97 interestingly enough.
Odds are that the heat treat is messed up on his receiver or someone drilled the holes out of spec. He has enough info now to decide his next steps and since I wrote most of this already, I decided to post it in case it helps someone else.
Accessing the 1968 AKM Armorer’s Manual
I am going to try hosting his huge armorer’s manual PDF file and see how it goes. If people have problems downloading it, I’ll just remove the link – click here for the 64MB PDF file. Note, I am not the owner or creator of that file. Someone did us a huge favor by taking the time to scan in all the pages and share it. It is in Russian and has a ton of diagrams.
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A few years ago, I bought a 1969 Polish Radom Circle 11 AKM kit from Arms of America. It has laminate furniture, matching parts and they populated a new Polish Chrome Hammer Forged (CHF) barrel with the front, gas and rear sight blocks. Furthermore, it was headspaced. I double checked that before I pushed out the barrel pin and then the barrel – that’s where things got interesting.
Pressing Out The Barrel
I have a 30 ton H-style hydraulic press with a 20 ton air-over-hydraulic bottle. The thing is a brute and have used it many, many times over the years on gun and car projects. There are a few things you learn over the years – 20 tons is 40,000 pounds and is a serious amount of pressure – steel parts can bend, break or even shatter under those loads. You learn to go slow, watch carefully feel the pump and listen. I also learned long ago to use the air to move the ram quickly but always do the real work by hand for those very reasons – I’ve bent the crap out of stuff in years past because you can’t tell what is going on.
I wear a full face shield when working with a press. I’m not joking when I say things can go bad fast when there is a lot of pressure. When you push out a barrel, you just don’t expect a ton of pressure from a new kit – at least I don’t. I’ve had some real hairy barrel pins and barrels in years past when dealing with surplus… but not on a new kit with a populated barrel … not until now.
Pressing Out the Barrel
As you can guess, the barrel did not press out easily. I had to apply a boatload pressure – way more than average. So much that I put a 3/4″ piece of plywood between me and the trunnion/barrel assembly. I was also checking and double-checking that my barrel press tool squarely on just the barrel and not a part of the trunnion – guys I was nervous.
I reached the point where I knew I was squarely on the barrel and something had to give. I was whacking on the press trying to shock the barrel out and I kept upping the pressure – pump, whack, pump, whack… Finally the barrel came free like a gun shot. Guys- do you remember the old Romy kits where the pins and barrels sometimes felt like you were taking your life into your own hands? That’s what this felt like.
I actually inspected the front trunnion very carefully looking for cracks. I then inspected the chamber end of the barrel – nice and smooth – remarkably smooth. No signs of galling. Ditto on the inside of the trunnion. I suspect that someone was using some kind of press system that included a barrel support and slammed that new barrel in using a level of force I couldn’t do without damaging parts. I noted to myself that reassembly was probably going to be just as colorful.
Building The Kit
Nothing new about building the kit – I had fun. In the below photo, the front trunnion and rivets are just sitting there. I was mocking things up and they are not actually set. I installed the trigger guard taking care to orient the selector stop properly and using a rubber band to keep the assembly together as I used my press and an AK-Builder trigger guard rivet jig to do the job.
The rubber band keeps the receiver down on the trigger guard jig so the rivet, selector stop and trigger guard all stay in place while you move around. The AK-Builder jig really does a nice job.Here, everything is drilled and seems good to go.
So let’s get back to the main point of this blog post and why you are probably reading this – what do you do when the interference fit is too tight and the barrel will not go into the trunnion all the way.
Life Got Colorful Trying to Press The Barrel Back In
Yeah, that tight fit came back to haunt me. I tried polishing the trunnion and applying non-seize. Usually this works for me but when I went to press the barrel back in, it would not go. I saw the barrel begin to deflect in the press and immediately stopped. Let me explain what I mean by deflect – a material will bend so much and spring back into place. When I saw the barrel begin to deflect, I immediately stopped – it was taking way too much pressure and I was risking bending the barrel permanently. It was time to press the barrel back out and rethink the situation.
Here’s my barrel and my receiver. I double-checked the barrel to make sure I did not bend it – I got lucky. I always get worried if I see the barrel start to deflect/bend — they don’t always return to true.
So, what this confirmed for me was the someone slammed this thing together – hard. An AK barrel is press fit into the trunnion. To do this, the barrel is a tad bigger than the hole made for it in the trunnion by about 0.0010-.0026″ (0 .025-0.065mm) according to Robert Forbus who is a true machinist and has shared a ton with the AK community – click here for his page). At the tighter end (around 0.002″) it is getting hard, if not outright impossible, for someone to press the barrel into the front trunnion without the proper specialized barrel press equipment that supports the barrel. I have a big press but nothing to properly support the barrel in these high-pressure situations. It would likely warp like a wet noodle if I just kept adding pressure.
I don’t own a machine shop but I am a redneck with a shop. I needed to open up the barrel channel in the trunnion and opted to use an OEM brand brake hone. Why? Because I’ve used these small bore hones in the past for other things and was pretty sure it would work for this too.
I also need to point out that I have no way to accurately measure the barrel or the trunnion so I figured I would remove a bit and try to install the barrel, remove a bit and try, over and over until it went in. The next picture shows my OEM hone (and the Lisle is virtually identical):
This is an OEM Tool brand brake hone and the Lisle unit looks virtually identical.
Take a look at the above picture – by tightening the knurled nut at the base of the spring, you can apply more and more pressure to the 220-grit stones at the end of the arms. (The Lisle tool’s stones are 240 grit purely FYI – not a big difference.) I just used the basic pressure and did not increase it. Life lesson for me years ago – it’s easier to take more material off than it is to put it back on.
I applied cutting oil to the trunnion liberally and then slid the hone in and out with my drill on slow speed. I would do this for a bit, clean stuff, and then tested how far the barrel goes into the trunnion by hand and then keep removing more. This is not the time or place to get impatient.
By the way, OEM makes fine 400 grit stones that you can swap into place and use to polish the interior further if you . I got the job done with the 220 grit stones and silver Permatex anti-seize compound. If I ad the 400 grit stones handy at the time, I would have done so but I did not. Also, be sure to clean out the grit/dust before you try to reinsert your barrel.
My one action photo and it was blurry! You get the idea. Keep it lubed with the cutting oil and keep moving the unit in and out so you are polishing the whole barrel channel.
This is a down and dirty “git ‘er done” approach and will make machinists cringe. I go slow and test — I would push the barrel in, test and the press it back out if need be. [Click here to see how to make a barrel backout tool].
*IF* you see a bur or squished rivet protruding in the trunnion, then carefully grind that down with a Dremel and polish with the hone. Don’t try to do it all with the hone or you will be removing material elsewhere that you may need – the arms are spring loaded and independent so they will go where ever they can. This is a pro and con.
After a couple of tries, the barrel went all the way in with the press. To be safe, I confirmed the head space using real Manson brand 7.62×39 gages (use real gages folks and treat them well – don’t go cheap). The barrel headspaced just fine so I pressed in the pin and finished the rifle up.
Bottom line, a brake hone can help you carefully remove steel from the front trunnion and get a tight fitting barrel to go in. It worked wonders on this 1969 cold warrior that is now ready to go to the range.
The 1969 Polish AKM rebuilt and ready for the range!The rifle is wearing one of our Polish Tantal/AKM grips as a 922r compliance part – we make them by hand here in Michigan from a glass fiber reinforced polymer.
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Guys, I must confess that I have a coffee addiction 🙂 As most of you know, I am into AK rifles as well. As part of that interest, I have read every biography I could find of Mikhail Timofeyevich Kalashnikov to try and better understand what led to the creation of the AK-47 and the eventual family of Kalashnikov designs.
Recently I was searching on Amazon and surprisingly found a coffee cup with a great photo of a young Kalashnikov that was tastefully done and, of courcase, had to order it. I had to wait a few weeks as it shipped from Germany.
When it arrived, I was surprised that the graphic was a different color than what the Amazon ad depicted. I thought about returning it but I do like the cup. The following shows you the cup that arrived – it is pretty cool and the color has grown on me.
My wife’s reaction was “Why did you buy another coffee cup?” To which I answered “But honey, this is Kalashnikov” at which she just turned around while shaking her head 🙂
In case you are looking for a conversation piece, check out this cup. Here’s the listing on Amazon.
7/3/2019 Update: It’s holding up just fine. It does make for a cool conversation piece when people use it. “Who is this guy?” is usually how it starts 🙂
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I am really enjoying these videos that Kalashnikov Concern in Russia is producing. In this video, Vladimir Onokoy, a technical consultant with the Kalashnikov and experienced AK armorer, discusses the Hungarian AK evolution with Pavel Pticin, founder of the AK-info.ru web portal, who has extensive AK knowledge.
I’ve always liked Hungarian AKs and found them to be high quality. Over the years I’ve built several AMD-65s and an AMMS. The kits all had original barrels and I was impressed by the fit and finish of the parts plus the rifles just ran and ran with no problems. They are definitely unique AK variants and I was actually really interested to watch this video and learned quite a bit.
Vladimir actually showed photos of a modified AK-63D that he encountered in Somalia. He mentioned how very impressed he was that it was still running with very little maintenance for close to 20 years.
This is one of Vladimir’s photos of the Somalian AK. Pavel noted it was likely an AK-63D with a cut down barrel, modified gas block and an AMD-65 muzzle break. One can’t help but wonder who did the work and why.
The video is just over 12 minutes and they discuss the early AK-55 rifle that is very similar to the Type 2 AK-47 with a milled receiver. They then move to a discussion of the AKM-63 (I’ve always heard it referred to as the AMD-63 in the US) with its distinctive handguard and grips plus other design differences.
As you may know, I own Ronin’s Grips and we make replica AMD grips. In one of the funniest gun video lines ever, Vladimir noted that the designer who decided to put an identical pistol grip at the front but simply reverse it deserved a medal! The Hungarians wanted to add it to improve accuracy and control under full auto fire.
Both Vladimir and Pavel noted that the front grip made reloading problematic and Vladimir pointed out that he had encountered rifles with the front grip cut down to reduce interference with loading magazines.
I finally got the best explanation ever as to why they used that bluish colored plastic. When the Hungarians decided to experiment with and move to polymer stocks, they lacked the ability to manufacture the base plastic. Because they were a Socialist country aligned with the USSR, the only plastic they could find that they could buy and import was a bluish plastic intended for dish making! You know what, that makes sense to me and what I will explain going forward.
The blue color is because the only plastic they could buy abroad was intended for dish making!
Lastly, they brought up some great examples of unique features you will see in the AKM/AMD rifles:
Distinctive pistol grip design
Metal lower handguard with no gas tube cover
The selector notches are labeled with an infinity diagram for full auto and a “1” for semi-auto.
The rear sight leaf has an “A” on it
The Hungarians used unique selector markings – the infinity loop is for full auto and the “1” is for semi-auto.The rear sight leaf has an “A” on it.
Here’s the video
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I will do a more In-Depth series of posts about building this rifle later. It is a Polish WBP kit l at the heart from arms of America with a Polish cold hammer-forged Barrel. The internals are installed in a Childers Guns receiver. The trigger is from ALG and I absolutely love it. I kid you not, this is now the only trigger I will use because it is so good.
The muzzle brake is a JMAC RRD-4C and boy does it eliminate muzzle climb. It made the rifle very controllable even during rapid fire.
The optic is a vortex Crossfire. The furniture is original polish Beryl with one of our US made 922r Beryl grips.
In the following video, this is my buddy Niko doing the shooting and while he is tall and wiry you can tell that the full-power Golden Eagle hundred and twenty four grain FMJ 7.62 x39 round is not moving him much at all.
The build turned out to be extremely reliable and accurate. Like I said I will post more details later but I’m thrilled with the results and had to jump the gun and share this video.
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Folks, once in a while I find out a snap judgement I made is very wrong. I was watching AK Build videos on Youtube and ran across this video with a very young man with long hair and anime shirt sitting down to talk about building an AK. I almost snorted because it must be some kind of a gag. Within the first five minutes I realized this young man was very knowledgeable, articulate and very capable at demonstrating how to build an AK. I was floored. I almost missed this because my snap judgement was so off. Wow.
This young man assembled a 55:59 long video showing you how to do an AK build with a manufactured receiver using a virgin barrel and he explains things along the way. To give you an idea of the quality, this video was posted in May 2013, has had 104,441 views, 1,114 thumbs up approvals and only 74 thumbs down. Folks, that is remarkable.
I am sharing a number of photos from the video to get you to realize this is really good. He steps you through everything including aligning the blocks on the barrels, the barrel to the receiver, drilling pin holes, headspacing, setting rivets and then final assembly, including installation of the fire control group (FCG), function testing, installing the furniture, and finally winding up with applying Alumahyde II from Brownells as the finish. I’d honestly say it is the best AK build video I have seen thus far that takes you all the way through the process. This is really worth your time.
P.S. The music and anime at the end is a nice touch 🙂
If you want to learn more, check out these other two video by bfgmovies:
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The NRA did a nice American Rifleman TV segment on the Chinese Type 56. It’s only 5:37 long and worth your time.
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You know folks, I miss the old Romanian Garda kits. I literally built about a dozen of them trying different variations on rivets, screws, welding and so forth. You could get them from $79-119 with the barrel and sometimes even a Tapco G2 fire control group (FCG) included. Copes, Centerfire, DPH and others had pallets of them. My wife would give me the eye any time a box showed up from one of them 🙂
That was the good times and then thanks to yet another ridiculous ATF ruling, the kits with barrels were forbidden for import, the well dried up and prices rose. I actually cut most of the completed rifles up and sold them for parts when kit prices went in the $300+ range. I sure had a ton of fun with friends and family at the range. What I personally enjoyed most was making them. Boy, I made a ton of mistakes along the way but learned too and also learned to respect a lot of concepts that Kalashnikov and his designers put into the rifles including pushing for reliability, simplicity, and so forth.
At any rate, I was going through some photos from January 2013 and thought I would share a few pictures of guns that ran like tops. These two rifles work great and I learned a ton making them. The finishes are shades of Minwax stain with hand rubbed urethane stain on top. I eventually moved to boiled linseed oil but that was long after I built these. I always liked seing how the stain would take to the wood. This is also before I started making grips – the wood one is from Ironwood and I don’t recall who made the plastic one. The finish would have been air dried Duracoat on these.
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Yeah, these things were like $79-99 in June 2006 so I did a lot of playing around including experimenting with weld builds. I still have this one and it runs just fine. The welds were done with a HF 120 Volt MIG welder running an ArC02 shielding gas. Basically I did plug welds in place of rivets but did some extra welding on the back trunnion as I expected more stress there. The lower rails were installed with a 120 Volt Harbor Freight Spot Welder with an AK-Builder tong installed.
My basic conclusion is that welding is fine for casual use rifles but rivets are the way to go with hard use. The tricks are to take your time, do plug welds and watch your heat. Your not trying to weld the heck out everything – just to get a decent plug weld to lock the parts into position in place of a rivet. You’ll notice that for the critical front trunnion, I actually drilled the holes in the receiver and plug welded into the trunnion that had the rivets drilled out.
I use a flap sanding wheel on my angle die grinder to smooth everything down.
A drill bit with the right diameter to line the lower rails up with the front trunnion is used to position the lower rail for spot welding in place.
I went for overkill welding in the rear and put in a few extra beads to take up stress.
Welding in the center support and sanded it down too
This is the rifle ready for testing.
I did Duracoat on this build and two big recommendations I would make to folks who choose to use the air dry Duracoat are to at least abrasive blast the surface and absolutely wait the full amount of time indicated for curing, which is 1-2 weeks or something like that. If you don’t do these two things, when you move the selector lever, it will scratch the finish off right to the bare metal. I only use bake on finishes now. I’ve had great luck with blasting, parking and then applying Molyresin on top but this last step could be whatever finish you want. The parkerizing is a terrific surface for a finish to really grab a hold of. A bake on finish is really the way to go with the top coat.
If I new they were going to go up so much in value, I would have done rivets. Heck, I would have done all the rifles using rivets had I known. I was just having a lot of fun and learning a ton.
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