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Another 7.62x25

5K views 39 replies 14 participants last post by  Coils 
#1 ·
First of all, BIG thanks to rahatlakhoom for doing the welding I couldn't do with my buddy's 90 amp mig. Also thanks goes to anyone else who has built one (I did a LOT of research).

This is my 3rd gun (also have a Saiga 223 and a Remington 11-48 12ga) and my first build. I come from a hobbyist machining background, that experience made this build a lot easier than it would have been. I started with a AMD-65 barrelless kit and a PPsh 16" barrel. I'll list the highlights that set it apart from others.
-The receiver was shortened nearly an inch and a quarter.
-The top cover is hinged at the rear sight block so the rear sight can maintain a zero.
-The front sight was welded to the gas block at 3/8" over the standard height to align with the HK rear.
-The barrel had to be sleeved in 3 places to fit the trunnion, hg retainer and FSB.
-Mag catches were welded to PPs-43 magazines to fit in an aluminum internal magwell.

It was running at about 85% efficiency with S&B ammo. But now I got a case of polish surplus and the firing pin isn't puncturing the hard primers. I reworked it a bit and it should be working better now.
The main problem I've been having is that sometimes it will short stroke, not resetting the hammer (NOT hammer follow) or ejecting the cartridge. Its quite puzzling since when it works, it has a nice crisp kick. When it short strokes, the kick is very weak. I think more polishing and filing of the rails would fix the short stroking.






[video=youtube;N2_2FSxefiU]http://www.youtube.com/watch?v=N2_2FSxefiU#normal]aksh[/video]
 
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#2 ·
Niiice! I like the Krinkov-style top cover.

Are you using the standard-length recoil spring or did you cut one down? You might have too much spring for it to cycle reliably. If necessary, you can wind a replacement from thinner music wire wrapped around a dowel.

Are you sure the hole in the gas block is properly aligned with the one in the barrel?

Is the gas piston going far enough up into the gas block? As long as it's not bottoming out inside the block, you might try fitting a washer between the back of the piston and the bolt carrier. The longer stroke would provide more kick to the carrier.

How far back does the bolt carrier travel when it's working correctly? A small chunk of modeling clay on the buffer will tell you. Don't use too much; you don't want to bottom the carrier out on the clay.

Do you have access to any other ammo? You might have a bad batch, or some that's mixed from more than one batch.

I don't know if it's a valid test, but I removed the hammer and recoil spring from my AKM while I was fitting the side rails, and decided they were good enough when I could point the muzzle down, let go of the bolt carrier, and the rifle would go into battery with no urging. My ejector was binding the bolt when I started, and it took a little grinding to get everything to clear properly.
 
#4 ·
Are you using the standard-length recoil spring or did you cut one down? You might have too much spring for it to cycle reliably.
Are you sure the hole in the gas block is properly aligned with the one in the barrel?
Is the gas piston going far enough up into the gas block? As long as it's not bottoming out inside the block, you might try fitting a washer between the back of the piston and the bolt carrier. The longer stroke would provide more kick to the carrier.
How far back does the bolt carrier travel when it's working correctly? A small chunk of modeling clay on the buffer will tell you. Don't use too much; you don't want to bottom the carrier out on the clay.
Do you have access to any other ammo? You might have a bad batch, or some that's mixed from more than one batch.
I don't know if it's a valid test, but I removed the hammer and recoil spring from my AKM while I was fitting the side rails, and decided they were good enough when I could point the muzzle down, let go of the bolt carrier, and the rifle would go into battery with no urging. My ejector was binding the bolt when I started, and it took a little grinding to get everything to clear properly.
Sorry I didn't put this in the first post, but its blowback, not gas operated. The piston is there only to provide a guide for the bolt carrier. I'm still using the standard recoil spring, maybe one day I'll cut a couple inches off. The carrier recoils all the way back to the buffer, I can tell from the marks on it. The plastic piece behind the buffer is just a spacer so the bolt doesn't travel past the hammer and get hung up.
That test you mentioned for the smoothness of the action sounds good, I'll have to try it.

How is the bolt setup in the carrier, is it fixed or can it be removed yet?
Thanks, the bolt can be rotated out of the carrier the opposite way a standard ak bolt is removed. I have a set screw in the carrier to hold it in place but I found that its not needed.
 
#3 ·
Nice build, really nice. Thanks for the pics too.

-Mag catches were welded to PPs-43 magazines to fit in an aluminum internal magwell.
That's a great idea.

How is the bolt setup in the carrier, is it fixed or can it be removed yet?
 
#5 ·
Sorry I didn't put this in the first post, but its blowback,
that is what I guessed by looking at the bolt in the carrier. Nice looking build did you take any pre assembly pictures of the barrel, trunion , mags etc

I lke the build a lot. some close up pics of the mag lugs and the internal mag well would be apreaciated. I was thinking of just welding lugs to my mags as well. does your mag hookin the front like a Normal AK or is it only held by the rear release and just slid up into a mag well??

some close ups of the carrier and bolt mods would be nice.

to check carrier travel just put some thin strips of tape over the slot were the charge handel travels space the tape every 1/4" apart and were the handel stops tearing them off is the amount of travel.
 
#6 ·

Sorry it took so long to reply, but here is the only picture I have of the build right now. My computer died a few weeks ago so I lost everything. Hopefully I'll be able to get all the pictures back soon. Anyway, the picture shows the two aluminum plates that go on either side of the magazine. They're a little oversized since the magazines vary in width (I only have three magazines currently, only two have tabs but all are different widths). Not pictured is the bullet guide/forward part of the magazine well. Its also aluminum and goes up tight against the front of the magazine. The magazine is held in by the rear tab and the tightness of the magazine well.

The bolt carrier does recoil back all the way, it just doesn't do it all the time. There has to be a burr or something on the underside of the receiver rails I'm overlooking. I haven't had much time to look (college student).

I have some questions regarding heat treating. Since I did a lot of grinding on the major parts of the gun, I'm thinking I should go back and heat treat the necessities before they deform any more than they have. One area I have noticed slight deformations is the rear of the bolt since that is what pushes the hammer back upon recoil. It created a burr that made it pretty hard to remove the firing pin. Thats also a concern of mine, the firing pin since I ground down both sides. The third potential problem area is the carrier stop. I took about 3/8" off the carrier here when I was setting the headspace but made sure to leave the trunnion carrier stop unmodified.

So that brings me to the questions. I know the rear of the bolt has to be hardened. I think I'll be ok to just heat that area and not the whole bolt so as to not mess up the welds on the face. I also think that spot heat treating the carrier where it hits the trunnion would be better than doing the whole thing. Next, the firing pin. Should I heat treat the whole thing? I did a search through google and ended up with a bunch of conflicting information. Some say only the primer end needs to be heat treated, some say only the hammer end. Some say tempering to blue or straw is better, some say that drawing at 400* for an hour is better. So which is best?
 
#7 ·
I like the idea of the bullet guide being part of the mag well and not the trunion. this would make tuning thunds easier.

I dont know what to think on the bolt getting damaged. is there a way to put a hardend collar around it or some thing to protect it?? I suspose you could just temper the end others here are better at the heat tread end of things.

would love to see lots more pictures of it. Im working on a couple now (slowly) I like the mag being held in by just the mag latch and mag well fit.
 
#9 ·
still think this is a nice build.

dont feel bad about your pix.... ive got a good camera and still take lousy pix. :)
 
#12 ·
nice build!

I like the mag well plates especially.
could you post pix of the bullet guide. (I don't think I overlooked it in the pix)

whered you get the 16 inch ppsh barrel?
how much?
is it a true 16" or just welded pipe on a ppsh smg/pistol barrel?

good job building this considering you're a college student who probably works and goes to school full time!
 
#13 ·
The bullet guide is pictured above, the last picture in post #8. Its aluminum for now, I'll be remaking it in steel soon.

I got the barrel from here Buymilsurp.com, Your source for military surplus. under PPsh-43 parts
Looking back, I'd rather go the original barrel + welded pipe route so I could profile it like an AK barrel. The 16" pps barrel is too thin for AK components, I made bushings for the trunnion, rear sight block and the handguard retainer. I used a piece of brass shim stock to wrap around the barrel under the front sight block since the diameters were too close for a bushing. On the up side, the barrel is threaded for 14x1mm LH, but thats a moot point for me thanks to the AWB. I ground them off.

Heres a slightly better picture of the underside of the mag well

And the whole gun in my messy garage

I heat treated the parts I was talking about above. Aside from lighting the oil on fire when doing the carrier, it went well. All parts were tempered to blue/straw. I also fixed the cant in the front sight by drilling out the holes and adding larger pins, added a rail to the top cover and more securely mounted the rear sight. Also threw on an AMD cleaning rod. Completely useless for cleaning because its too short, but it helps secure the lower handguard. Still have yet to fire it.
 
#17 ·
Very nice work rk5n- I especially admire the clean work you did in fabricating the gas block/sight base. I try to avoid welding because mine usually ends up looking like a tumor. Yours looks great.

xebec
ITS NOT A TOOMAH
 
#16 ·
Im starting to think my son might like one of these for Xmas. Id do it in sporter/hunter style with optics and a 5 or 10 round mag to keep the weight down for him super light barrel, light weight plastic stock or a aluminum tube stock maybe some alumium barrel parts ect , I want it light so he can carry it and hold it up. I really need to get baack on track i bought the reamer the mags the blankes ect I need to get one done.

I really llike the mag well it gives me some ideas.
 
#18 ·
That is a nice clean conversion.
I did one earlier this year. I used a pps-43 magwell.
It's blowback also, and has huge recoil energy.
I use Romanian surp primarily. The Yugo and Bulgarian surp is
brutally strong. S&B is nice and clean, but too expensive for me.
I can fire 70 rds before everything starts fouling out. I just hose the
fcg and innards down with WD-40 and continue.

 
#19 ·
I can fire 70 rds before everything starts fouling out. I just hose the
fcg and innards down with WD-40 and continue.
Ar you getting a lot of fouling on the bolt & in that area while shooting it? Sounds like the bolt is starting to open while the powder is still burning in the barrel. Might want to try a stronger recoil spring?
 
#21 ·
I just came across this problem when I went shooting on Sunday. After about 50 rounds of polish surplus, the gun would short stroke and mis-feed almost every other round. I'd wipe everything down and oil the rails and the gun will be back to normal. On the plus side, normal was a short stroke or misfeed every 20-30 rounds. I ended up putting 120 rounds through it.

I'm thinking that the bolt and carrier are too light. If anything I've reduced 10-20% of the bolt carrier's mass and SMG's have heavy bolts. I'm going to replace the piston with a solid steel rod to fill up the gas tube to try and add a few ounces.

Also I need to replace the feed ramp with a steel one slightly lower than the current aluminum one. The second magazine I modified is slightly loose and too low and misfeeds more often than the first one I made.

The third problem: the charging handle broke off... again. Trying to operate this gun when dirty without a charging handle and with the bad magazine is one of the most frustrating gun related experiences I can think of. Every other shot I had to undo the top cover, remove the magazine, clear the jam, pull the bolt carrier back, insert the magazine, let go of the carrier and close the top cover. The problem is that welding on the funky alloy the bolt carrier is made of is very very hard. I'm planning on making a new charging handle and either bolting it in or pressing and staking it in to avoid it ever breaking off again.
 
#24 ·
COILS,

just wanted to throw this at you for consideration......

you mentioned the bolt may be opening too soon and letting a lot of the powder foul up the set up...

YEP that could be very possible on a blow back gun, happens all the time if the bolt is too light.

and while a stiffer recoil spring will help with what he already mentioned about the "too much" recoil.

it wont really help much on this. if he gets one stiff enough it will. but what really is the issue on blowback guns and especially 7.62x25 guns is the BOLT WEIGHT.

the bolt mass has to supply the dampening effect for just that mili second.

this is the most important part of a blow back operated gun. lots of guys try to just control it with a spring, and sometimes its real easy to cover the stretch, which meant your weight was only off a tiny bit.

thats why when we do conversions of fixed pin bolts to floaters we try to always make sure the weight is back to where it started. that way the mass is right for the power of the round.

by just adding "more spring" a lot of times the spring has to be so strong to do the job that it causes feeding issues after that.

a good way to ad mass to an AK bolt is to put some lead into where the recoil spring went up at the top. he obviously doesnt need to cycle as far as the original set up.

its just an idea to think about.

but for manageable recoil on a 7.62x25 with a 16" barrel in blowback.... your bolt should weigh near 550 - 600 grms or so.

thats where the pps41,43, m56, p7 and others all come in at.

sdk
 
#33 ·
rk5n you keep mentioning welds on your bolt face and it has me wondering how you welded up your bolt face: did you use a bushing or did you use just some spot welds to reduce the diameter of the bolt face?

All this is thinking you used a x39 bolt and carrier.

Also how high was your ammo/mag well guide? What configuration did you use? Was it 2 ramps are a unibrow type ramp? The foto looks like a 2 ramp style but can't be sure. If you could, please post some measurements.
 
#34 ·
Not trying to speak for rk5n,
We welded a reducer sleeve onto the face of a 39 bolt.
Typical of the 2xtm type of conversion.
I've done about 10 of these and all seem to be satisfactory.
 
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