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More work on .45ACP conversion.

8K views 34 replies 12 participants last post by  Rhino_66 
#1 · (Edited)
Well, since the Gunco WV shoot is next weekend, I figured I'd better get some more work done. This project has been simmering slowly for over a year and a half, so the heat is now being turned up! This project began in fall of 2003. A lot of early discussion with HCPookie, Vis, Geodykt, Daewoo, Golovko, U.S.M.C.Man, and a few others, helped me develop my initial design. A lot of that time was spent calculating the clearances and cut dimensions. A lot more time was spent using Photoshop and MSPaint to move portions of photos around to get an idea of what problems would evolve and what to do about them. Here's where I'm at, right now.

The gray paint makes it easier to see the areas that were machined. The raw machined surfaces wash out with the camera flash and are difficult to see.




This is the basic machining done to the bolt carrier. The cuts were made before any welding because I wanted to make sure all the interferences were accounted for. The cocking handle has been removed, the clearance slot for the bolt lug is cut, the ejection clearance cut is made, and the firing pin access hole is drilled. Portions of the cuts will be filled with weld once the primary machine work is completed. The rotation channel will be welded up and a notch for the cocking handle will be cut.




This shows the position of the bolt in the carrier. The bolt has been cut to the proper length. The triangular tab on the back of the carrier has been cut flush with the back surface. The bolt will eventually be welded into place.




This is a close up of the cut bolt and carrier. I considered filling the 2 upper bolt grooves with weld and reshaping the bolt, but I think I'll just silver-solder the back end and leave all the welding at the front...




This pic shows the clearance channel for the bolt lug. This is what allows the bolt to slide straight in before final welding. There are several large gaps that will be filled with weld and ground to shape before final assembly. This will allow for a more solid attachment, and prevent the possibility of cracking.

The angled cut for ejection clearance can be clearly seen in this pic. It's tough to see in this picture, but this is the bolt that I opened up to fit the .45ACP cartridge. The extractor only required minor grinding with a dremel stone to get the groove to match the cup diameter.

With the bolt in this position, the ejector lines up correctly with the slot in the bolt. The 7.62 ejector rail will work perfectly with the conversion.




This pic shows the hammer engagement with the modified bolt and carrier. The striking face of the hammer is perfectly flat against the back of the carrier. Because I designed this for blowback operation, the bolt cannot be positioned in the forward position. For proper operation, the bolt must be shortened, moved closer to the back of the carrier, and rotated. The bolt is shortened 0.800". Because of the bolt being shortened, the hammer will not make contact. My design calls for moving the trunnion back the same distance that the bolt was shortened. This will position the back of the carrier in line with the hammer face in the same place that the original bolt stem was positioned. Hammer function is smooth and the carrier easily pushes it back down to engage the trigger and disconnector.





I performed the alignment checks using a standard OOW receiver. This pic shows the carrier moved back exactly 0.800" from the postive stop of the trunnion. This lines the carrier up perfectly with the hammer. I will be using an IBE battle blank for the .45 receiver. The dimples in a standard receiver prevent the magazine from fitting into the receiver far enough. The thicker blank is a little easier to weld on, as well. By only shortening the receiver by 0.800", standard handguards can be used without modification.




This pic shows the carrier seated against the positive stop of the trunnion. When the barrel is installed, the breech face will be right up against the face of the bolt. This gap between the carrier and trunnion is unavoidable, because of the position of the bolt. The barrel will take up most of the gap, but I will add a small piece of sheet steel to the top cover to keep debris out of the receiver. It will also look a little cleaner. This gap is present on the Bizon, too. The Bizon top cover is stamped to cover the gap.




This is one modification that early on I realized was necessary after deciding to weld the bolt in the carrier. The firing pin retaining pin cannot be removed once installed, unless a clearance hole is drilled. Once the bolt location is determined, the clearance hole was marked and then milled. I used 1/8" carbide end mills for this step. I started with a ball end mill to make the hole in the underside of the carrier. Then I switched to a standard end mill to punch through the top of the carrier. The rounded surface inside the recoil spring tube prevents drilling through the material. The sharp corners of the mill bit easily cut into the curved surface and allowed the holes to line up without breaking a drill or screwing up the hole.



My next steps will be to fill in the carrier slots with weld, attach the cocking handle, and then permanently attach the bolt. After that is completed, I can work on the receiver and barrel. After that, I can work on the magwell and think about test firing. WHEW!!!!
 
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#27 ·
hcpookie said:
That sleeve looks nice. What did you use for the source material? I'm looking around for a piece of schedule 80 pipe in a suitable diameter.
I cheated. I used a 3/4-16 nut as the sleeve. The area at the breech end of the barrel with the acme threads was only about 5/8" long. The nut I used was over 3/4" thick, so there was plenty of overhang to cut off. I used a grade 8 nut and my silver solder is only 500 degree melting point, so the sleeve is actually harder than the barrel. At least it seems that way when the cutting tool makes the change from nut to barrel.

After I got the barrel threaded I tinned the threads with silver solder and ran my die back over them. I sand blasted the nut, tinned it, and chased the threads with the tap. I wiped the threads with a little flux and spun the nut onto the barrel, leaving it a little loose. I heated the parts with my oxy/acetylene torch until the solder flowed. Then I tightened the nut and let it cool. After everything was cooled, I chucked it in the lathe, trimmed the breech end flush and turned the flats off the nut.

I'm guessing you're getting ready to sleeve your 9mm barrel. You'll probably have to make your own tubing for your sleeve if you want a thick wall on it. A little time on the lathe won't be too bad for you.
 
#28 ·
Cephus said:
YOU THINK YOU'RE PRETTY SLICK DON'T YA THERE KID ,AND I THINK SO TO. THAT WAS A GOOD ONE AND YOU DO HAVE A HARDER SPOT THERE THAN THE BARRELCAUSE THE GRADE EIGHT IS SOME TOUGH STUFF.SO AARE YA GOING TO LEAVE THE STRIPPERS ALONE LONG ENOUGH TOP HAVE THIS READY FOR AUGUST OR WHAT.LMAO
I'll just have to do the "Gentlemen's club" thing through the week. That'll leave my weekends free for work... :rofl:
 
#29 ·
"AND the last pic.

The paragraph under the last pic clearly explains how I am dealing with the firing pin retainer pin. The extractor pin is not blocked in any way by the carrier."

Sorry, I guess I mis-read it earlier. I too thought about welding and opening a hole to access the pin, but I like to be sneakier than that, so I made mine actually LOCK together with positive locking lugs made from the original locking lugs.... I have just got a Photobucket account, so Im gonna take some GOOOD close up high res pics of the parts locked together and seperated. Once y'all SEE how I did it, you're gonna slap yourselves and go *DUH*...if you can use a dremel and a MIG welder, you can do the mods I did. Will go faster w/a TIG and a mill, but not impossible for the DIYer. Anyway, thanks for the info on your bolt, I agree a 1-piece bolt would be the way to go. Im contemplating using some 1.25" square tubing and trying to make one from scratch following the model below (see attached pic)...

Good luck with your project, keep us informed. Im hanging on my seat w/each passing day!!! :)
 

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#30 ·
IF you look close you can see the line between the bolt head and the carrier, running thru the push-bar thing at the bottom (the thing that actually PUSHES the rounds into the chamber...) The bolt head rotates counter-clockwise approx 30* and then unlocks allowing you to seperate the 2. When installed into the receiver the bolt head's old locking lugs follow the bottom rail (just like in an AK during extraction) to keep it from rotating out of position. The 2 are locked so solid it might as well be welded. ALL the forces are transferred backwards into 2 seperate lug areas upon firing. When extracting unfired rounds the carrier pulls on the front of the bolt which is also lugged in very well. No problems as yet but only shot about 20 thru it...

When it's fully "in battery" the hammer sits on the firing pin/bolt tail perfectly, just as happens in a real AK. I didnt bother with trying to trim the tail down or whatever because thats NOT the way it was designed... I DID add some extra steel to the carrier to protect the bolt tail from the hammer during cocking, also the extra metal insures that the hammer goes down ALL the way and engages the sear. I was having issues with the sear not catching.... Be careful with this, it can cause all sortas problems (out of battery fire, unintentional FA discharges, etc etc)....

PEACE!
 
#31 · (Edited)
Well, another weekend means another update on the progress of the conversion...



In this pic I'm turning the finish diameter (0.908") for the breech end. Once I had the breech diameter turned, I flipped the barrel end for end and took care of the other diameters.





This pic shows the majority of the work completed. I made REALLY small cuts since I wasn't using a shaft support. I was only taking 0.005" radius cuts (0.010" off of the diameter) to avoid flexing the barrel. That takes a LOT more time, but it works well. I had the carriage feed set pretty slow and used a really narrow pointed cutter (as seen in the first pic). That gave a nice finish that polished up easily with some emery cloth.





This is the semi-finished barrel. The big step in the middle cannot be avoided. The M1A1 barrel has a big taper at this point. Unfortunately, this is right where my handguard retainer needs to be. I'm going to install a sleeve about 3/4" long to add the necessary length for the retainer. After that, the only thing needed will be to cut the grooves for the retainer lugs and the notch for the lock, then the barrel will be finished.





It's not easy to see in the resized pics, but there is a radius at each of the diameter transitions. I used a rounded cutter to leave a small radius in the corner. A sharp 90 degree corner is a perfect place for a crack to start.

I think I'm going to see if a Chinese gas block will look better than the RPK part. The RPK gas block has a HUGE diameter sleeve for the barrel and I think it will look a little odd. Another option would be a Yugo gas block, as it's the same diameter as the Chinese piece. I would prefer to keep it as traditional looking as possible, so I think the Chinese will be the better choice.
 
#33 ·
hcpookie said:
reamers! use a reamer to open that gas block up. It won't be doing anything anyway.

Don't really need to ream the RPK block...

I considered sleeving the block, but it would look funny. I also considered sleeving the barrel with a longer tube, but I don't think it'll be the greatest solution.

The Chinese gas block has an I.D. of 0.634". My barrel has an O.D. of 0.670" where the gas block needs to go. There's no way I'm going to reduce the barrel diameter any further, but I can easily ream the Chinese or Yugo block to fit.




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