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Master Endmill Breaker
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Discussion Starter · #1 · (Edited)
Okay, I'd like some honest opinions on some machine work that I'm going to performing in the near future. I didn't get a chance over the Christmas weekend to get any machine work done.

Basically I will be opening up an AK 7.62 bolt to fit a .45ACP case. The easiest method for this is to use a 0.500" end mill and just hog it out to the right depth. The bolt in the pic is screwed up because I trusted the marking on the plastic sleeve rather than measuring the actual tool. I grabbed an end mill that was marked 1/2" on the sleeve and turned out to be 17/32". Consequently, the bolt cup is 0.030" too big now. Nobody to blame but myself...

I'm looking for suggestions for reshaping the extractor to line up with the new bolt cup.

I have a dremel grinding stone that just happens to be 1/2" in diameter and thin enough to fit into the slot. Any suggestions on what other tooling would be available for this cut. Maybe a 1/2" x1/16" keyseat cutter? I can get them in carbide or TiN coated, so working on the heat treated part isn't an issue. It may be easier to anneal the extractor, machine the slot with a HS cutter (CHEAP!!!), and re-heat treat it.



This pic shows the cup milled to an incorrect depth. The cup is about 0.030" too deep.

For the firing pin, I'm just going to trim it down a bunch. Right now, without any intervention, the firing pin sticks through far enough to possibly slam fire a .45 cartridge. The pic shows the pin pushed all the way forward into the bolt. I will have to cut at least half of the exposed tip off to prevent it from punching through the primers.

BTW, the camera is a Nikon Coolpix 5200. I bought it as a gift for myself this afternoon. The pic was taken at just under 2 inches away from the part. Plan on seeing more pics like this as the machine work gets further along...
 

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You might want to shorten that firing pin; it looks like it will pierce the primer. Good luck and keep us up to date on your work.
 

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Master Endmill Breaker
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Discussion Starter · #6 · (Edited)
I already mentioned the firing pin issue. That one was a given considering how much I milled down into the cup.

I do have a couple dremel fittings that will work for this. The problem will be holding the extractor. I can clamp it down through the pivot pin hole, but I'll just have to be careful when trimming it.

I would like to use the keyseat cutter because I can clamp the extractor in the vise and work from the top. The Dremel option requires me to work from the bottom end of the piece. Even though the Dremel is easily maneuverable, I find more comfort in the the X,Y,Z axis controls of the mill.

I think I'll just do the dremel thing and be done with it. There will be less setup required and I can check the fit without worrying about returning the piece to zero.

 

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Happy Camper
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I like the dremel idea.

I will like to see the fit after you cut it down. Seems like the extractor will now be too far forward in relation to the cartridge. Then again not really sure...

I'm thinking that IF that requires more work than enlarging that opening, we'll have to make a completely new extractor. Not a big project, but will need to use the mill to get it right. Then harden it up.

Cephus, not sure Kasenit is a good idea here, because it adds a layer of material to the part, I think it could interfere with the fit of the extractor in the bolt. However if the clearance between the extractor and the bolt is loose enough, and the layer of Kasenit is thin enough, it would work.
 

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Happy Camper
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You know I was looking at an AK-74 ejector and wondered - can you put a '74 ejector on a '47 kit? Wonder if, by mixing ejectors made for different calibers, if that would help matters?

OTOH, this is a small part and seems that we could mill it by using a grade-8 bolt, and use the mill + dremel to fit it just right. Since it is such a small part, the mill may be too cumbersome, making a dremel job more suitable, even if you were to make 20 of them.

Hrm now you got me wanting to go out to the garage! I *know* that with the proper drill bits and dremel attachments this could be built from a grade-8 bolt. Here's how I think it would be best to do it:
1. Lathe or mill the shaft to the proper diameter
2. Dremel the end to the proper shape for the ejector face
3. Drill the pin holes
4. Cut the notches
5. Cut off the ejector to the proper length.

Keeping it on the bolt until the end would give you something to clamp into the vise and chuck into the lathe jaws. A mill + file could be used if you had to, but a lathe would be faster. I've done the drill press + file for a quick lathe job, and found the oscillation of the press would always make you file off-center. Not a big deal for small parts so here it may be suitable. You just need a properly-sized shaft.

What do you think about that?
 

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Master Endmill Breaker
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Discussion Starter · #10 · (Edited)
The 5.45 extractor is going to be a perfect fit for 7.62x25, 9x18, and 9mm. With the .45, I only need to grind (or mill) 0.020" deeper into the side of the notch to make the extractor match the 0.500" diameter of the new cup.

There will literally only be a couple bumps with the rounded side of the stone required to get the bevel the way I want it.

The amount of trimming is so slight, that I can't justify turning a new extractor. Of course, now that I've said that, I will probably screw up the extractor and have to fabricate a new one anyway. I do have a second extractor from the other bolt to work with, so I'm not worried.

If I were going to consider producing these things (which I'm not), 11/32" round stock would be the easiest material to start with for the extractors. A 1/2"x1/16" keyseat cutter would be great for the groove and the pivot pin would need about a #28 hole. An 11/64" hole would be needed for the spring.

With all the holiday stuff out of the way, I should have time to work on the bolt this coming weekend.

Mounting the bolt in the carrier is a completely different story. I will need to build up some areas of the bolt to make attachment easier. TIG would be the easiest method to get the build-up needed. There's also a fair amount of welding needed on the carrier to close up some gaps. Once the parts are built up and remachined, they can be welded together.
 

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Master Endmill Breaker
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Discussion Starter · #11 · (Edited)
Well, I got the new bolt milled. I have to say that I am MUCH happier with this one. Not only is this bolt milled to the right diameter, it's milled to the right depth. When I milled the first bolt, it must have moved in the vise. The depth wound up being more than it should have been.

The depth is set correctly in the new bolt. The depth of the cup is exactly 0.125". The head of the .45 case sticks out of the Thompson barrel 0.145". This give me a 0.020" gap. My incorrectly milled bolt had interference from the extractor against the case head. The extractor in the correct bolt will only need to have the notch and lip deepened to match the case diameter.

Now for some pics of the correct and incorrect bolts...


Correct bolt on the left. SERIOUSLY screwed up bolt on the right.




Correct cup depth on the left. SERIOUSLY screwed up bolt on the right.




.45ACP in correct bolt on left. .45ACP in SERIOUSLY screwed up bolt on right. Notice the big gap around the incorrectly milled bolt.



I have to say that carbide is the way to go when working on hardened steel. The carbide cut through the heat-treated steel like butter.
 

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Master Endmill Breaker
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1,367 Posts
Discussion Starter · #12 ·
With the bolt milled correctly, I can get to work on the carrier. There will be some welding required to build up a couple areas on the bolt once the carrier is finished.

The lug on the bolt that follows the twist channel in the carrier will be extended all the way to the front of the bolt face.

The entire quarter of the bolt head where the extractor resides will be built up back to the shoulder. This will provide additional surface for welding when the bolt is permanently attached to the carrier.

The twist channel will be filled in with weld. The cocking handle will be cut off and moved back about 3/4". A channel will be milled in the carrier for the twist lug, allowing the bolt to slide straight back. The back of the bolt will be welded to the carrier. Once the bolt is welded into the carrier, I'll silver-solder the area around the bolt stem to seal it and keep debris from building up in the gap.
 

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strong work, I think what you are doing is freaking AWSOME, how will you be able to take the firing pin out for cleaning, not that you reall have to, break-cleaner cleans it out for me 99.9% of the time.
 

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Master Endmill Breaker
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Discussion Starter · #14 ·
Thanks! I'm glad people are interested in this project. 9mm coversions will be easier, but only because the bolt won't need modification to fit the casing. The bolt lug, carrier mods, and receiver shortening will still be necessary.

Before welding the bolt in place I will drill a hole all the way through the recoil spring tube in the carrier. The hole will line up with the firing pin retainer pin hole in the bolt in it's final position. The pin can then be removed and installed almost as easily as a normal AK.

The extractor pin doesn't get covered up when the stripper lug is pointed straight down, so removing the extractor won't be an issue.

The cocking handle will have to be moved back. If left in it's original position, empty casings will not be ejected. They'll just bounce off the overhang back into the receiver and jam up the action.

The bolt will be cut flush with the end of the carrier. If left long, it will punch into the stock tang. The triangular tab sticking off the back of the carrier will also be cut flush. The tab will definitely interfere with the hammer. With the tab cut off, a recoil buffer is necessary to keep the carrier from possibly coming off the top rails at full recoil. The triangular tab fits into the recoil spring fixture at full recoil. Without it, the carrier could hop up enough to jam on the cutouts in the top rails.

If someone were to do a conversion in .44 magnum or .357 magnum, there should be enough gas to cycle the action. That would be a fun conversion, too! It would need less modification, maybe only a barrel and magazine well conversion. Use Desert Eagle magazines and just make a sheet metal magwell housing to weld to the receiver.
 

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Happy Camper
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Rhino_66 said:
The bolt will be cut flush with the end of the carrier. If left long, it will punch into the stock tang. The triangular tab sticking off the back of the carrier will also be cut flush. The tab will definitely interfere with the hammer. With the tab cut off, a recoil buffer is necessary to keep the carrier from possibly coming off the top rails at full recoil. The triangular tab fits into the recoil spring fixture at full recoil. Without it, the carrier could hop up enough to jam on the cutouts in the top rails.
Careful here - someone pointed out that this spur is what keeps the hammer from causing an out-of-battery misfire by physically blocking the firing pin from the hammer until in full battery. Granted, this would only happen if your FCG malfunctioned and caused a slam fire, but still it would be catastrophic.

I haven't played with hand-cycling enough to confirm this. Just be sure that the slam fires won't be a concern here.
 

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Master Endmill Breaker
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Discussion Starter · #16 ·
hcpookie said:
Careful here - someone pointed out that this spur is what keeps the hammer from causing an out-of-battery misfire by physically blocking the firing pin from the hammer until in full battery. Granted, this would only happen if your FCG malfunctioned and caused a slam fire, but still it would be catastrophic.

I haven't played with hand-cycling enough to confirm this. Just be sure that the slam fires won't be a concern here.
The original function of the spur is just to keep the carrier from coming off the rails when firing the rifle. With a select-fire rifle, out-of-battery firing in semi-auto mode is essentially impossible because of the auto-sear. If the FCG failed (i.e. trigger hook broke off) while in semi or full-auto, the magazine would empty, but the hammer strike would only happen when the carrier tripped the auto-sear. The bolt would be rotated and locked in the trunnion, so there would be no problem with out-of-battery explosion.

On semi-auto rifles, it is extremely possible for out-of-battery firing to occur. This could be due to a faulty FCG or poor gunsmithing. Looking at my PMKMS, the bolt is engaged in the trunnion but not rotated into the locking lugs when the back end of the carrier (not the spur) is lined up with the center support. The spur prevents the hammer from coming in contact with the firing pin until the bolt lugs are at least partially rotated into the trunnion. I think this is just a fortunate coincidence for us civies. Take a look at a couple of yours and check when the bolt rotation stops. Mine stops at just about the same point as when the hammer makes contact with the bolt stem.

Since the Bizon (and my .45 conversion) are blowback, the situation would be similar to a Sten or Thompson sear failure. The rifle would slam-fire until empty. Since it's blowback, there wouldn't be a catastrophic explosion (except in my pants...) until the cartridge was chambered and forward momentum stopped. I've seen a runaway .45 with bad handloads. The primers weren't set deep enough and it fired every time the slide locked home. 7 rounds of full-auto goes REALLY quick... The look on the shooter's face was unforgettable.

Removing the spur for pistol caliber is unavoidable. With the spur left on the carrier and the receiver shortened, the hammer will not be able to strike the firing pin. The original Bizon carrier doesn't have the spur to prevent slam-fires, so I'm not going to sweat it. Of course the first few magazines won't be loaded full when I test it...

Looking at these 2 Bizon pics on your site makes me a little more confident in the blowback operation without the spur.





If I were using .44 Mag or .357 Mag, I would be worried...
 

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looking good so far. Pistol caliber conversions are always interesting.
 

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Master Endmill Breaker
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Discussion Starter · #18 ·
BUMP!

Since Pookie's website is back up, the pics are working.
 

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Happy Camper
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Yeah sorry about the site - went away on a business trip and that evening I had an update download that required a reboot - just got back in town to click "OK" and apparently it took the network offline while waiting for the "OK". Now all updates are automatic, so that shouldn't happen again... we shall see.

Hrm. That's interesting. You know I'll have to look more closely at one of my AKs while hand-cycling it to see if the spur does anything at all, other than the rail jumping.
 
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