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Thread: .243 win based on AK innards

  1. #21
    Gunco Member kragaxe's Avatar
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    Cool, thanks to everyone for the info and links! Being low on funds, and making the bolt...I might as well make the others also. It's been almost 20 yrs since I woked as a machinist, so I need the practice for some upcoming projects!!! After talking this evening with the guy who owns the mill, we're going to transport it over to my place and set it up this weekend so I'll have unlimited use for a couple months or so.

    I'll have to check out the saiga bolt. Sounds like what I plan on doing is pretty much what they did. I'm making the third lug from the bottom section. Adding the forward extension allows me to keep the same thickness/depth of the section while making a lug out of the forward most section of it. I couldn't figure out why the lugs were offset from each other either. Mine will all be the same plane.

    I've been looking over the trunnion section. It seems pretty straight forward. There's a few cuts I won't bo doing since I'm altering it a little. There's lots of tooling marks left in the yugo one, so it wasn't too bad to figure out what tools and from what direction cuts were made. Some of the cuts look like they were made to allow room for the other bits to come in from a different direction and serve no other function. There's a few spots where I can beef it up without causing bolt interference. I figure a lot of it's going to be "cut to fit" until everything is where I want it and it locks up properly. The barrel can be moved in and out for the final headspacing. I'm using a block of O1 tool steel which isn't bad about warping during heat treat and is through-hardening and easy to get down into the spring hardness levels. I'll take photos of all the set-ups and tooling as I do it. If it all works, there'll be a nice photo-how-to...if it doesn't work, well, there'll be a nice photo-how-not-to!

    After studying the carrier and seeing how they did their's, man what a pain. Looks like it was done starting with some round stock and the main bolt hole done. After that, anything that doesn't look like a bolt was milled off. Not really difficult cuts...just very time consuming when the mill I'm using is a smaller one and can't do thick passes. I did some .050" cuts when doing a FAL upper and it liked to have killed the machine! I think I might just get a carrier. I have one, but since I won't be scavenging the other parts, I want to keep it with the rest of the M70 parts and just make the M70 at some point. Carriers pop up regularly on gunbroker for ~$25-35.

  2. #22
    TRX
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    When I first took an AK apart I saw all the machine marks from dull cutters and thought, "Man, why didn't they just do all these parts as investment castings?" Darned if I can find any sprue marks anywhere on the parts I have, nor can I come up with a reason why they'd duplicate such cobby machine work. If all you have to do is one part for a pattern, why not make it nice?

    I have a milled receiver on hand, and it looks for all the world like they took a Big Chunk O' Steel and whittled 90% of it away. WTF? No wonder it looks like the cutters were dull...

    Oh, and for something practical - if you build the back using a narrowed AKM rear trunnion, you can use AKM stocks if you narrow the spigot slightly. The selection of fixed stocks to fit the Yugo receiver is small, and prices are considerably more than AKM stuff. And Yugo trunnions are expensive, too.

    I love the looks of the Yugo underfolder, but I just couldn't come to terms with the idea of firing a big bore cartridge with a T-shirt and the Yugo's horseshoe-shaped buttplate.

  3. #23
    No Hope For Me 1biggun's Avatar
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    I would think accuracy is a higher priority than sheer velocity, so you probably won't even use a really hot load anyway. I would not recommend loads that land on the right-hand side of the charts! Stay away from the red line and you *should* be OK.
    I agree and most of my most accurate loads under max. running fast powders to maximise a short barrel can get trickey and possably dangerious. The advantage of a 308 or in this case a 243 is more case capacity to burn a slower powder to get higher speeds at less pressure.

    If I were going to make any thing Id concentrate on the bolt. the trunion and carrier are all still avaliable releativly inexpensivly. a saiga bolt is slightly wider across the two lugs than a standard and has the bottom area were it slides over the mag extended down. I would not change the length or any thing else except possably the stem size so it fits a larger carrier, id just copy it just slightly narrower across the lugs to fit a standard trunion. If you can make all of it more power to you.

    if you do a trunion make it for a threaded barrel with a larger ID so a big bre acn be done. some thing like the threads on a M70 Win barrel would be nice.

  4. #24
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    I just saw some pictures of (reportedly Bulgarian) FSBs and GBs with the telltale round marks of diecast ejector pins. The ones on my Romanian still look like milled to me...

  5. #25
    Gunco Member kragaxe's Avatar
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    Got quite a bit of shop time this past week. Mostly finishing up some knife projects, but did a bit on the rilfe as well.

    I got the block fit into the magwell where the mag ejector with be. I'll do the trigger guard and pistolgrip mounting nut tomorrow.

    I got quite a bit done on the trunnion. Most of time was spent working out exactly what I wanted to do with regards to what gets extended/modified. Once that was worked out, the rest of the time was just standing there at the mill. I borrowed a mini-mill for a couple months, so I'm limited on tooling and thickness of cuts. 90% of my tooling is HSS. It did NOT like normalized steel of any alloy. I have four projects going on at once and all use medium carbon steel and alloy steel. I broke down and just spent a day doing annealing cycles. Below are a couple pics of the process.




    First, marry a woman that loves you and accepts your hobbies, then drag your furnace inside and set it up on the kitchen counter if that's the only 20 A breaker in the house.

    I put in the biggest hunks and brought the peices up to 1575*F, and let soak long enough to ensure they were heated throughout. Then I shoved in all the other parts and let eaqualize at 1575*. I next brought it down to 1400* and held for four hours. Then, I turned off the furnace and let cool down overnight (~10 hours). The parts were still about 350* 10 hours later. Man, what a diffwerence it made on the 4130!

  6. #26
    Gunco Member kragaxe's Avatar
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    I started to use a hunk of O1 for the trunnion, but it wasn't wide enough to do what I wanted, plus it's a bitch to machine. I have a huge hunk of 4130 I use as a sharp-cornered object with my forgework and knifemaking. It's just a 2 x 4 x 10 hunk. My dad took his chopsaw back, my cutoff bandsaw died last year...so I just used the drill press and an angle grinder with cutoff disks.



    The resulting hunk was one of the blocks in the above annealing pics. After that, I flattened all the surfaces and brought it down to the starting size I wanted. I used the M70AB2 as a template...kind of. I widened the whole thing by 0.050" and my locking shoulders will all be in the same plane. I blued it with ink and scribed several reference lines.



    After making the rectangular block, I did the upper main cutout. This makes it easy to mark and measure the next couple cuts.



    After that, I began roughing out the upper half of the opening. In order to keep small radius corners, I did this with a 1/4" endmill. In the annealed state, I was taking 0.035" cuts...which is pretty good for one of these mini-mills on steel! Here's where I stopped this evening. Next, I'll slot the walls. The surface there is where the rail surfaces will line up. It makes a nice guide for the keyway cutter.



    Next, I'll do the barrel hole....maybe. I'm hoping I can use a 4 jaw, independent jaw chuck on a small lathe and chuck it up. This would make very short work of the barrel hole and the locking shoulders. "IF" it works, I'll start with some large deming bits and open it up to 63/64th ( no particular reason other than that's what I have). Then I'll chuck up a 1" mill bit and ream it all the way down to where the shoulders are. Then, I'll go back to the mill, do the underside cutouts and clean up some of the corners and finish out the remaining cuts.

    P.S. Ideally, you'd do the hole first. For one, it's easier to drill/mill out a hole in a symmetric block. Secondly, if you screw it up, you can mill the block down until the hole is centered where you want it...and if you totally blow it...there's not much time invested in it yet.

  7. #27
    No Hope For Me 1biggun's Avatar
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    well this is getting interesting. do you have a boring bar/ head for the mill??? thats what I would thought to use for the barrel hole. damm wish I had a furnace that would be what I need to do my 50 bmg project.

    I hope this all works out for you if you pull it off you will likely be the first home builder I have seen make his own trunion. If you can get a look at a saiga 308 trunion and bolt in regards to the lugs being wider. If you need pics I can likely send you some. If your going to make it, make it stronger than whats already out there.

  8. #28
    Gunco Member kragaxe's Avatar
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    My bolt lugs will only be about 0.020" wider in radius and the same length, but there will be three of them. The shoulders in the trunnion are beefier than the M70 and my MAK90 as well.

    One of the drawbacks of the minimill is the lack of horsepower. I really need the next size up for doing these bigger holes and using the larger bits. If we actually sell out old house this Fall, I'll be getting a good general purpose one for myself. It'll be nice to have my own equipment and not have to beg borrow and steal!

    I picked up my electric furnaces at surplus auctions for the Universities around here. I paid $40 for the one in the pic...and I got five or six old film projectors, a bag of assorted other crap and an overhead projector that came with it on the pallet. Texas A&M changed their auction format. Now they use the online stuff that runs continuous. Much harder to find a deal. Being in Houston now I'll have to see what U of H and the various teaching hospitals use for their surplus sales. Ought to be lots of lab furnaces from the hospitals.

    For metalwork, just make sure you get a muffled furnace. Ceramic kilns often have exposed elements. Those are way to easy to break elements in!

  9. #29
    Gunco Member kragaxe's Avatar
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    I have a 1" cobalt end mill and deming bits from 5/8-1". The lathe owner said "no problem" to my idea. It was nice to hear an affirmative response! His only concern was non-symmetry throwing the chuck out of balance. Once I showed him the actual dimensions he didn't think it would be a problem at all. I guess when i said "hunk of 4130" he envisioned a 4 x 6 hunk or similar!

    I started on the rear trunnion tonight. This is being made from 1.25" square mild steel. I'm making a custom folding stock for it. I really like the looks of the FAL para stocks, but being a stingy bastard I can't bring myself to fork over that much for a stock...just to cut and mod it! I think it will actually be kinda of fun making one. Stocks are always something I'm needing, and I never see "exactly" what I want in one. It'll be nice to finally have what I want. I think I have a pretty good idea for the locking mechanism on it as well, but I'll wait until it's done before I show it .


    Some of the cuts in the trunnion seem to be strictly for tool clearance. I noticed when using a 1/4" endmill, I need to cut an angle on some edges to get the tooling where it needs to be for final cuts and these angles all coincide with where the angled cuts are in the original. That and rounded and angled cuts just make it look more "refined and graceful" (if you can actually use graceful and AK in the same sentence!) as opposed to just a cut up block of steel.

  10. #30
    Gunco Member kragaxe's Avatar
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    Stock attachment will have to wait until the weekend...we're off to have a baby now!

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