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7.62x25 Gas Operated AK pistol

9K views 42 replies 23 participants last post by  Girth 
#1 ·
It ain’t done yet but its working great, so I couldn’t wait to unveil. Most of the parts are from an AMD 65 AK47. The bolt and carrier are from an AK74. The barrel and mags are from a PPSH 41. The magwell is from Lichtenberg. The flash hider is from an L1A1.


Here are the details.

Barrel It is a PPSH 41 barrel. The rear of the barrel was turned down and sleeved (and a tack weld) to fit the AMD 65 front trunnion. Another sleeve was installed for the rear sight block. The barrel was turned to fit the gas block and front sight block of the AMD 65. A sleeve was added to the barrel in front of the gas block to fit the front hand guard retainer. The barrel was threaded for LH 14x1 threads. A cut was taken from the chamber end of the barrel for extractor clearance. Minor radiusing of the lower half of the chamber lip was done after a round caught on it during testing. The gas vent hole started at 0.125” and grew to 0.170” during testing.

Flash Hider I drilled out an L1A1 flash hider and pressed in a steel bushing. The bushing was then drilled out to 13 mm and tapped for LH 14x1 threads.

Receiver I traced an AK Builder flat (love your flats man!) onto 0.040” thick 4130 steel and cut out everything but the magwell. I did some measurements and hacked out my estimate of the opening. I bent the receiver on my own jig. The magwell opening was cut too big as was as the back clearance notch for the bolt carrier. A new receiver is planned before final finishing.

 

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#2 · (Edited)
Fire Control Group AMD 65. The hammer face and top were reprofiled to reduce force needed during recoil to recock hammer. Lots of experimental welding and grinding. A reduced force hammer spring was made using 0.045” diameter music wire bent to the stock configuration but with only one leg.

Bolt Stock AK74

Bolt Carrier It is from an AK74 with 1 inch of length removed from just behind the piston threads. The carrier was welded back together using a brass rod inserted to align the pieces before welding. The carrier and piston assembly was shortened because I moved the gas port closer to the chamber to tap into higher gas pressure. The photo shows it compared to a standard bolt carrier.

Gas Piston Custom made stainless steel one inch in length (not counting threads) The clearance between the gas piston and gas block is about 0.005 inches.

Recoil Spring During testing, an inch at a time was removed from the recoil spring until three inches was removed to reduce the force exerted on the bolt carrier. The metal loops that retain the spring were shortened to reduce the overall length of the assembly and fit it to the shortened bolt carrier.

Gas Tube Custom machined tube with the locking ring from an AMD 65 gas tube spot welded on. The majority of the tube interior diameter is for the large diameter of the bolt carrier. An interior taper is machined on the front end to guide the gas piston to the gas block. The gas block vent holes are only partially obscured.

Front Trunnion An AMD 65 trunnion was cut to fit the mag well up close to the barrel throat. (The photos show the cutting and fitting) Cuts were made using a 4” thin abrasive disk on a hand held grinder. A stream of water was used to keep the trunnion cool and maintain the trunnion’s heat treatment. The cuts did not go up into the locking lugs. The bullet guide was removed and ground so that the AK74 bolt could rotate up the left side. ( The AK74 bolt head has a greater distance from the back of the locking lug to the front of the head than the AK47.) The guide was riveted back into place and later tack welded when the cuts to fit the mag well cut into the rivet area.
 

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#3 · (Edited)
Mag Well The mag well is a 7.62x25 assembly from Lichtenberg Research. A large relief cut was made on the top right front so that the mag well mated up tight against the right front trunnion locking lug. A lot of the mag well’s feed ramp was ground down for clearance as the bolt rotates into the locked position. I am not sure the rounds touch the feed ramp on their way into the chamber. Miscellaneous other filing, grinding, etc. was required to fit the mag well.

Gas Block The AMD 65 gas block was used. The block was mounted to the barrel so that the rear of the gas block is 4.94” from the chamber face of the barrel. That places the gas port about 5.30” from the chamber face of the barrel.

Rear Site Block The AMD 65 rear site block was cut so that the block could be moved as far back as possible and still eject shells. I should have only cut the right side of the block, but in my enthusiasm I cut the left side as well. When I shortened the top cover I left a “leg” to fill the gap I created on the left side.
 

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#4 ·
Lower Hand Guard The stock AMD hand guard was cut in length so that the hand guard retainer would be located just in front of the gas block. The rear mounting tabs were spot welded back in and the front grip mounting hole was filled in with a piece of sheet metal MIG welded in. After the gas block was installed on the barrel, a sleeve was pressed onto the barrel to provide the correct diameter for the hand guard retainer.

Trigger Guard Since the mag well is shorter in length than a standard AK mag well, I made a longer trigger guard out of 0.050” thick 4130 steel. I didn’t want to tear apart a good AK trigger guard so I also made a mag catch lever and spring. The spring was made from 0.045” music wire. Because the mag catch lever was so far forward, I placed a small block of steel between the mag catch and the trigger opening to give a surface for the mag catch spring to push against. This steel block is held in place by two button head screws at this time.

Rear Trunnion The AMD trunnion was used. A steel plug was milled to fill the mounting hole for the original folding stock. With the plug clamped in place, a hole was drilled vertically down through an existing hole on the right side of the trunnion and the plug was pinned in place. A quick weld ensures it isn’t coming out.

After a lot of fitting and testing, the action is cycling perfectly with drums or stick mags. Test firing was done with surplus Chinese ammo and some Sellier & Bellot ammo. Accuracy seemed good at the pistol range. The front sight was stuck and I couldn’t adjust the impact point at the range. I fixed it when I got home and look forward to getting back to the range.
 

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#11 ·
Wow!!!!

That's what I call building one from scratch!!! Well done.
Ditto

Excellent work, thanks for sharing the info.



are you concerned about cutting into the trunion that much/ worried the locking lugs are not supported enough without the rest of the trunion?
I don't see a problem at all mainly because of it being a pistol caliber, now if it was still a rifle caliber I'd think it over a few time before trying it.
 
#9 ·
VERY NICE CAMERA WORK AND WRITE UP. NICE BUILD. AS SOON AS i DIGEST ALL THE WORK DONE ILL HAVE SOME QUESTIONS. THERE IS A SIMULAR BUILD OF SOME TYPE IN MY FUTURE. I WAS ORIGINALY THINKING 9MM BUT THE 7.62X25 HAS REALLY GOT MY ATTTENTION. I REALLY LIKE HOW YOU GOT THE MAG WELL UP CLOSE TO THE BARREL BY MODIFING THE TRUNION REMOVING THE FEED RAMP ECT.
 
#10 ·
Really impressive build, great writeup too! are you concerned about cutting into the trunion that much/ worried the locking lugs are not supported enough without the rest of the trunion? In any case, it does solve the magazine gap issue I'm facing. Don't mean to hijack your thread, but I'm building a 7.62x25mm gas op too:


here you can see the gap:


the rounds reach the end of the feed lips and still have almost a 1/2" to go before entering the barrel. Your 2xtm magwell placement eliminates that problem.
 
#14 ·
If I remember correctly, most of the metal I removed was thin compared to the metal higher up that extends back to the lugs. That thin metal would stabilize the lugs during extraction when the bolt is rotating and dragging against the lug. I am guessing (and you might say betting) that there more than enough material left to handle the forces generated by the 7.62x25 cartridge.

The recoil forces are alot less than what the original trunnion was designed for. I had to cut the recoil spring, make a weaker hammer spring and modify the hammer face just so the action would cycle reliably. Still, I should make a note to magniflux the lugs after the first 1000 rounds or so to check for cracks.

Thanks for the compliments guys.
 
#15 ·
If I remember correctly, most of the metal I removed was thin compared to the metal higher up that extends back to the lugs. That thin metal would stabilize the lugs during extraction when the bolt is rotating and dragging against the lug. I am guessing (and you might say betting) that there more than enough material left to handle the forces generated by the 7.62x25 cartridge.

The recoil forces are alot less than what the original trunnion was designed for. I had to cut the recoil spring, make a weaker hammer spring and modify the hammer face just so the action would cycle reliably. Still, I should make a note to magniflux the lugs after the first 1000 rounds or so to check for cracks.

Thanks for the compliments guys.

I WOULD KEEP A CLOSE EYE ON IT. I HOPE IT WOKS OUT FOR YOU. A BULGED YUGO TRUNION MIGHT HAVE BEEN A BETTER CHOICE AS ITS THICKER IN THAT AREA.
 
#17 ·
opinion only

Many of the sub guns in this caliber are blow back. As are many of the AK conversions.

Three inches of recoil spring were removed to allow cycling. The hammer spring change was for the same reason.

The rifle was overdesigned for a cartridge of about twice the energy.

Recoil lugs are not an issue.
 
#18 ·
SW -

I just now stumbled across your build thread - WOW Nicely done - great job on your write-up & pics too. You are one of the very few who's been able to get a gas-op in x25 going, and a pistol at that. Very impressive build, especialy the way you compacted the magwell & trunnion together. Thanks for posting it!

Steve
 
#19 ·
Thanks Steve!

I have the pistol taken apart to make a new receiver and clean up some earlier mistakes. I took the opportunity to take photos of the modifications made to the bolt carrier, trigger group and the custom trigger guard.

Modifications were made to the bolt carrier and hammer to reduce the force required to push the hammer back to the recocked position. The rear "nose" on the bolt carrier was extended to be just shorter than the firing pin position in the locked position. The hammer face was extended and recontoured to be as long as possible without interferring with the disconnector catching the hammer. The photos show the mods compared to stock pieces.

The modifications allowed the bolt carrier to push the hammer back furthur using the "nose" of the bolt carrier and the face of the hammer. It gives it more leverage for a longer time. Once the "nose" can no longer push on the hammer, the bottom of the bolt carrier begins to push on the hammer, but with less leverage. With this mod the hammer is nearly recocked by the time the bottom of the carrier starts to push on it. It reduces the force needed.

I stated in an earler posting that the hammer spring was made in the stock configuration from 0.045 music wire. It was actually made with only one leg as the photo shows. I had to add another spring to help reset the trigger. It is located on the right side of the trigger group and presses against the receiver to help push the right leg of the trigger back down. I haven't had any misfires with the lighter hammer strike.

The last photo shows the trigger guard I made. It was made to move the mag release forward to the new location. The square block of steel was made ti fill the gap and give the mag release spring something to press against. Two short button head allen screws were used to hold it in place. A selector stop plate was also made in a longer size.
 

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#21 ·
wow ive got no clue how i missed this build.

very very impressive and would love to have a set up in this as most of the people just go with blowback.

while id watch the trunnion for cracks as you said, with the reduced force your putting on there it would "seem" to be fine.

you offering any of this work as a conversion service..

or maybe some contact infor for the Litchendberg magwell deal?

thanks

sdk
 
#22 ·
I am strickly a hobbyist. No paying customer would be happy with my poor welding skills and slow pace of work. I think I bought that magwell back in August of 2008!

Lichtenburg Research is currently sold out of the mag wells according to thier web site. '+windowtitle+'

When they get enough interest they may do another run. I bought mine from what I think was thier second run. The mag well was a good starting point although I went on to cut it up in many ways. I even cracked a front spot weld at some point and had to zap it with the spot welder. ( I swear it was only a tap........with a 5lb hammer.)

Contact Lichtenberg and see what they say.
 
#23 ·
that magwell could be very handy in a lot of different builds so thanks for the link on that!

keep the info coming on your build. its very nice.
 
#25 · (Edited)
An update on the new receiver. As I mentioned earlier, I wanted to make a new receiver and correct several minor errors. Its a good chance to document building points. The first photo is the original receiver. Note the mag opening was larger than the seond photo of the new receiver. I cut the rear "flaps" of the mag well so that the receiver would cover more of the rear of the mag well.

The flat was made from 0.040" 4130 sheet steel. The mag well was only cut out on the bottom of the receiver before bending. The rest of the mag well profile was transferred from the first receiver using dykem blue after bending.

The front trunnion was fitted carefully to the front of the receiver. The first time I did this the barrel/trunnion had the barrel pointing slightly to the right. Live and learn!

The rails needed to be fitted next. I used AK builder rails. The ejector was hardened and the lower mag support rails were ground off. The photo shows original (top) and modified (below). (Not a perfect photo. Look for the shiney edge where I removed the mag suport rail) Grinding off the lower mag support is needed for mag well clearance.

Next the ejector needs to be moved forward for the shorter 7.62x25 cartridge. I cut the front off the left rail so that the ejector "point" was 0.275" from the front edge of the rail. The scrap piece of the rail is to be spot welded at the rear of the left rail to support the head of the bolt when it is inserted in the receiver. The last photo shows the old receiver with the two piece left rail spot welded into place.

I need to weld in the rails and do the final fitting of the mag well next. I'll keep this thread posted as I go along.
 

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#27 ·
im trying to follow and learn the ejector and bolt mods from both of you guys as this is the part that im really interested in getting down...
 
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