Bulgarian AK74 Barrel installation

[klewan]

What exactly is involved with installing an AK74 barrel? I've been thru the threads about build parties, can't find any detailed info about this.

There's a $95 barrel pressing tool from AK-Builder, can't tell exactly how it's used. AK-Builder make a big deal about all the stuff they do to headspace the barrel if you buy one of their kits, but then you have to take it all apart to finish the build and have to headspace it again. Is this necessary, or can you use a new US barrel and get it drilled and installed without having to be the Kalashnikov factory?


I'm thinking cool the barrel in dry ice and use the rosebud with the oxy-acetylene to heat the trunnion and tap those together instead of the brute force method.

I'd like to know any tips on headspacing, I'm thinking a couple of cartridges and some tape on the head. A friend is a graduate of the Lassen College gunsmith program. He showed me to use a couple of pieces of masking tape on the cartridge trick. If the bolt closes on one thickness of tape and is hard to close on two pieces, it's in spec for headspace.

There appears to be a pin or two that holds the barrel into the trunnion, any insights on how that is installed without butchering the barrel or trunnion?

Is it true you have to get a stamped parts kit, not a milled receiver kit? I didn't see the vendors making an effort to tell which one they were selling.

I'm thinking of getting a couple of Bulgarian AK74 kits, any opinions about Arms of America, What a Country, Atlantic or Apex versions. They're all about the same price but without actually seeing what they're selling, it's a real crapshoot.

[1lowluv]

I just got one from arms of America. Kit looks brand new. I'm in the same boat as you on the barrel instal. Ak builder will populate and headspace it for you if you send them your barrel, bolt and everything in front of it for 70 bucks

[Alex$]

What exactly is involved with installing an AK74 barrel? I've been thru the threads about build parties, can't find any detailed info about this.

There's a $95 barrel pressing tool from AK-Builder, can't tell exactly how it's used. AK-Builder make a big deal about all the stuff they do to headspace the barrel if you buy one of their kits, but then you have to take it all apart to finish the build and have to headspace it again. Is this necessary, or can you use a new US barrel and get it drilled and installed without having to be the Kalashnikov factory?

Yes


I'm thinking cool the barrel in dry ice and use the rosebud with the oxy-acetylene to heat the trunnion and tap those together instead of the brute force method.

you could try this, but unless you are careful you can change the hardness of the trunnion. Personally I would not use an oxy/ace rosebud.

I'd like to know any tips on headspacing, I'm thinking a couple of cartridges and some tape on the head. A friend is a graduate of the Lassen College gunsmith program. He showed me to use a couple of pieces of masking tape on the cartridge trick. If the bolt closes on one thickness of tape and is hard to close on two pieces, it's in spec for headspace.

First build I used the tape method, scarey first time you shoot it, but that gun is still running and passes headspace. (I have since bought gauges)

There appears to be a pin or two that holds the barrel into the trunnion, any insights on how that is installed without butchering the barrel or trunnion?

One barrel pin that is pressed in to keep barrel in headspace. Drill and ream hole to proper size, press in for proper interference fit.

Is it true you have to get a stamped parts kit, not a milled receiver kit? I didn't see the vendors making an effort to tell which one they were selling.

If you have a AK74 barrel, you will need a stamped kit

I'm thinking of getting a couple of Bulgarian AK74 kits, any opinions about Arms of America, What a Country, Atlantic or Apex versions. They're all about the same price but without actually seeing what they're selling, it's a real crapshoot.

I have had great purchases from all listed except Atlantic. But they are an advertiser here and are reputable.

see above

[kcstott]

The above information is correct.
Now as for cooling the barrel and heating the trunnion. I'm going to insult you here so bear with me.
Unless you know or can gage with a reasonable amount of certainty how hot you are getting the trunnion DO NOT TRY IT. All you have to do it get that trunnion over 800 degrees F and you just created a paper weight. You have the locking lugs for the bolt in there and if you make that trunnion to soft you will get lug set back and excessive headspace you may even get a failure to unlock meaning you can't open the bolt or you feel a lump in the action.

What I do is measure the barrel and trunnion and compare the two. I like no more then .0005" press fit. Stock from the two kits I've gotten is around .002"-.003" press which is damn tight.

So if you have the tools to measure it properly you can use emery cloth to polish the barrel tenon then press with a lot less force into the trunnion.

As for the Tape method of head spacing. No where is this ever appropriate to do except when it's a SHTF situation and you just need a quick a dirty way to get a weapon going.

The problem is you have no idea how small the factory cartridge is. You don't now if it's on the bigs side or the small side. So adding tape is making the cartridge longer but you have no idea where you started. The difference between Min and Max head space is .010" (go is zero and no go is plus .004" field is plus .008" and is approaching max.) Now granted it's an AK Meaning it's loose as a goose to begin with. It's still not a safe practice to follow. What happens when you have excessive head space is that the cartridge head will stretch and try to fire form to the chamber. As it is doing this if the headspace is bad enough the case head may separate from the body. When this happens, As the AK is not that great at handling gas protection the action will blow open and vent gas out the back of the chamber. It may blow the dust cover off and a few parts with it also. Buy or borrow a set of gages and do it correctly or spend the money to have someone else do it for you.

Now once the barrel is headspaced it doesn't need to be reheadspaced. Once you rivet the receiver on the trunnion you press the barrel back in aligning the pin hole to the groove in the barrel. You then verify the headspace with gages and press the pin in place. This is done because on a 12 ton press you can have the pin and groove misaligned enough to have an out of spec headspace and still press the pin in. The barrel will not self align, the pin will just punch a clean path.

[klewan]

Plan B; heat the trunnion in the oven at 400F.

I'm pretty well tooled up, have a metal lathe and BP with most of the popular tooling. All kinds of measuring stuff. So I can measure and machine the barrel to the necessary press fit.

I was planning on getting 3 or 4 different brands of 5.45x39 ammo and measure those versus the drawings of it. The gauge is nice, but I'd rather spend the $40 for one gauge on something else. I think I can do the headspace and not maim myself. I also have cerrosafe and will make a cast of the chamber so I will know what's in there.

Thanks for the advice.

[69Mach1]

Why don't you add a Harbor Freight 12 ton press to your impressive collection of tools. It will save your sanity....for $100.

[kcstott]

Plan B; heat the trunnion in the oven at 400F.

I'm pretty well tooled up, have a metal lathe and BP with most of the popular tooling. All kinds of measuring stuff. So I can measure and machine the barrel to the necessary press fit.

I was planning on getting 3 or 4 different brands of 5.45x39 ammo and measure those versus the drawings of it. The gauge is nice, but I'd rather spend the $40 for one gauge on something else. I think I can do the headspace and not maim myself. I also have cerrosafe and will make a cast of the chamber so I will know what's in there.

Thanks for the advice.

$53.99 for a set Go and No Go gages.

And you're asking for trouble with the heating of the trunnion. Get a press, or have someone do it for you. If you Knew how to take a .0005" cut on a lathe you wouldn't be asking how to headspace it.

[klewan]

Why don't you add a Harbor Freight 12 ton press to your impressive collection of tools. It will save your sanity....for $100.

I forgot to mention that, bought it in 1981 for $100. That was the first thing I bought from HF, with inflation that's about $250 today. No wonder it was so hard to afford much stuff back then, it was really expensive.

But since then I've accumulated a wood shop, auto repair, and the metal and reloading stuff. I buy something and never sell it, so it adds up.

[klewan]

$53.99 for a set Go and No Go gages.

And you're asking for trouble with the heating of the trunnion. Get a press, or have someone do it for you. If you Knew how to take a .0005" cut on a lathe you wouldn't be asking how to headspace it.

I know what headspace is; what I don't know is how AK headspacing is done. Regular rifle barrel is threaded and you cut the thread and shoulder to the correct length, screw the barrel into the receiver, drop in the gauge, see if the bolt closes on it. Or has too much space away from the bolt.

Turns out the Bulgarian is pinned. I remember 20 years ago listening to people in the gun store arguing about whether a threaded barrel SKS or AK was better than a pinned one. I didn't know what they were talking about back then, but now I have a lot better understanding.

I still like doing it the "Okie" way, I'm not going to have access to a gauge for every gun when I need it. So having a way to do it without waiting for UPS to deliver a gauge; I just like that.

I like adding some heat to get things together or apart. I used to work at the Ford plant that made the 9 1/2" third member. The one everybody in NASCAR and NHRA uses. There was a 13" diameter, carbide insert surfacing cutter, that was dull and needed to be changed. 1" allen screw held it on the spindle. I watched 3 guys tugging on a 6' cheater bar over the allen wrench trying to get it out. After an hour of fighting it and the line being down, the foreman called for one of the welding tractors to get over there.

This is a full size Ford farming tractor with a generator on the PTO, AC/DC stick welder, and Oxy-acetylene tanks. He fires up the rosebud and heated the allen screw for a minute, puts the allen wrench on it, gives it a tug and it's loose. Brute force is how I've messed up lot more things than using heat. They don't call it the "Blue Wrench" for nothing....You being down in San Diego, didn't see all the rusted crap we had in the midwest and further east. Just getting a brake drum off the rear axle could be half an hour a side to get that bugger off the axle that is was rusted to. And now we have infrared thermometers to check how hot that metal really is, no more heat sensitive crayon nonsense....

YMMV

[klewan]

Update,

I'd forgotten about youtube and took a look at those. All questions were answered there. If you want to find out how to do something, start there. You can watch somebody butcher something, or somebody do the most elegant bit of work you could imagine.

Then if you still have questions, do a search or ask at AKfiles.com.