MG47-308

Last Post: 11/2009
Retrieved: 01/15/2011
Updated: 05/22/2016

Okay, I've read all the 308 conversion threads and MG47 threads over and over. I still have a couple months until I can get back in the shop, but here is what I am planning:

A belt-fed, AK out of a Yugo RPK kit in .308, using the original finned RPK barrel, just reaming the chamber.

I have got SS's MG-47 plans, an RPK I cut to 19" to make a carbine that I am not particularly pleased with, an MG3 FT and TC on order, a good source for .308, and the desire to use disentigrating links.

I need a chamber reamer and a spare 1,000 hours. The question is, and I have found some folks that WANTED to do it, but what results have you had with reaming out the x39 chambers to .308. I know the whole .308 vs .311 issue and I am okay with that for a "proof of concept" build. I got the RPK kit a year ago with a shot out front couple of inches anyway so it is a good candidate.

Thoughts? Has anyone tried this yet?

1. stronger return spring and bigger ejection port

2. venting the gas tube to slow the bolt due to the impulse from the higher chamber pressure/ more gas.

3. position feedtray a little furthur back (I was thinking about 12mm) from the breach to give the round more distance to align and not have as sharp an angle (am I off on this one?)

4. thicker steel for reciever and after it works, weld it all up so if something catastrophic happens the path of least resistance is up through the feed tray and top cover.

From my own personal experience with my .308 conversion, I would consider the AK gas port too large - you'll beat the rifle to hell and back! Therefore, you could either

a) drill more vent holes on the gas tube

or

b) drill a smaller barrel, more in the size like on a FAL gas port.

"B" ovbiously assumes a new barrel, which I think will be better. I would not recommend plugging, then re-drilling the gas port. The gas port plug would be nothing more than a threaded insert, and would need to either be welded on, or a tapered fit at the outside edge like a cut-down bolt head, so that it would not "walk" down into the barrel and block it. That would be bad.

A tapered fit at the outside edge would assume you would cut a notch into the barrel for this extra material to reside, so that you could actually reinstall the gas port back onto the barrel.

Drilling more vent holes in the gas tube seems to be a far easier ordeal. You'll obviously be bleeding a great deal of gas away from its intended job - pushing the bullet down the barrel - so performance may be lackluster.

If you leave the port as-is and "simply" rechamber, if it works, it will not work well because the sheer amount of recoil energy will literally beat the gun apart. The rivets on the rear stock tang/trunion will be peened out from the excess force applied against them. The axis pins may also peen egg-shaped due to the excess force of the bolt carrier when cycling the action.

On my .308 conversion build, I cut 4 extra gas ports on my gas tube and that toned it down enough to work.

The receiver on the MG47ES is 1/8" thick v.s. .039 on a standard AK receiver. I don't think you need to go any thicker than 1/8". G3 receivers are no where that thick although they are deeper. My ES with a RPK front end weighs about 14 lbs. with a 1/8" thick receiver.

P.S. My son is building a M-76 in .308 with a heavy target barrel. The barrel threads on a Winchester and Ruger are 1"-16 TPI, which is just the right size to thread RPK trunnion which would give you a much stronger barrel to trunnion connection and you can put the gas block where you want and drill the gas port hole as small as needed to just cycle the action. I found that on a belt feed you need the gas pressure to push on the piston a lot longer before it's relieved to accuate the feed cam. Basically you need to convert a short stroke gas system to a long stroke gas system.

GETTING STARTED!

Well I am back and getting going. Unfortunately I am still in the "honey-do" phase of coming home and shop time is stolen in short bursts.

I stripped down my old RPK Carbine that I didn't like, rented a reamer, extension handle and go/no-go gauges from "reamer rentals" and did the chamber today.

For the record, that was EASY. If I was to do it again, the big extension T- handle they have is definately worth the extra $5. I just went slow, used lots of oil and took my time. It took me maybe an hour and a half, but now I have a yugo RPK barrel in 308, bolt opened up to the 308 head via dremel and headspaced perfectly. Just a little more to go, right??

What could go wrong?

After tapping the first three, I broke the first rule of tapping and chucked the tap up in my cordless drill (don't tell my dad, he'd whup my ass) but with oil all over had no problems.

Instead of the 1/2" angles, I used 3/4" for extra strength....aw who am I kidding, I bought the materials from memory and grabbed the 3/4. It worked fine though. I'll have to mod the FCG slightly from the plans, or I may just cut them down some.

I need to buy the rest of the cap screws, but it is going together well. Thanks again SS.

And the obligatory mock up.

 I really like your combination carry handle/top cover pivot pin. Very clever

Do you think that dropping the feed tray back 12mm from your original position is right? My main concern is that the feeding angle would be too sharp in the original position.

I would recommend that the nose of the bullet just enters the chamber when the base of the cartridge case leaves the belt link. The longer 7.62x51 case should put the base farther back than with the 7.63x39 so the feeding angle will be less anyway. Cntrailrider has had success with his feed tray farther back than mine though but you have to have the bolt traveling forward fast enough to throw the round into the chamber if it is mid air when it leaves the belt link and before it enters the chamber.

Lookin' real good. Not a good idea to have cartridges flying through the air (unsupported). Almost nosing in the chamber as it's leaving the link is best, and the path always seems rather steep. Height of your feed tray is critical, to overcome the steep angle.

Got the ejection port (super-sized) cut, and the trunion mounted. Now comes the hard stuff...

Got the lower rails made, the bolt is sliding as well as the barrel back on today. I sure do love this "screw build" and being able to take it apart and put it back together over and over. I may never smush a rivet again.

Looks great. From your last picture it looks like you are going to need to open up the ejection port on the left sideplate some more to get the brass to clear it.

Yep, I'm gonna wait until I get it sliding to know how much to open it up.

Got a lot done today:

got the upper rail and ejector done

Mounted up the FT and TC (sorry, I welded the bracket, not true to the design)

Made a bolt carrier extension, but out of steel and welded. We'll see if it holds. Still haven't decided exactly how I will do the FCG.

It strips dummy rounds off the belt, shoves them in the chamber, extracts and ejects great.

Lots of little adjustments and tweaks along the way, but this is a really fun build. If I don't blow myself up, I'll have to do another.

I have to say, having humped an M-60 and a 240G, this thing is going to be LIGHT. I can't wait!

I am curious about what you all think of if the gas tupe and vent holes etc can be left stock. Even a wild ass theory I will listen to. As I recall the VEPR uses a standard gas system, but will the pressure be up long enough for the belt feed?

Now the pictures...

Mustang

It looks really good and it feeds! I don't mind at all that you welded the pivot on but I am dissapointed that you didn't keep the combination red carry handle and pivot pin. (Mustang Carry Handle). LOL

As far as the gas relief holes in the gas tube, on all three of my belt feeds I had to have a very gas tight joint there and relief holes almost at the end of the stroke. You basiclly have to convert a short stroke gas system to a long stroke system in order to push the BC back all the way and actuate the feed cam. You might be able to do the same thing with a large gas port in the barrel. The 308 is a lot higher pressure than the 7.62x39 and may have enough impulse to through the BC back all the way with the standard setup. I believe DTM has some experance with this in his XT74 which shoots a high pressure cartridge.

Got it. I'll make it a long system. Also it sounds like the bolt group needs to be in the low 20oz as far as weight goes. Do you have thoughts on springs? I was going to try first with dual AK springs in front of the FCG like on your ES plans, but running like the other one that was done by DVAN. Do you think they will run it?

I tried to make a single AK spring work in the FCG on the ES but it just wasn't enough poop to do the job. I never tried a tandam side by side AK setup like DTM and DVAN though. What has worked for me is a M60 return spring available from Numrich. I used a old style multiple wound (Russki style) in the buttstock of the original MG47 prototype and the new style single wound spring in the hollow gas piston tube on the ES. Both worked.

The new style spring is less than $20.

It feeds!

Well kinda. It is rough! Using a bar to push it closed and a string to pull it back, it is smooth like butter without ammo. Drop in a dummy belt though and it goes, feeds, extracts ejects, the whole thing, but it is rough and beats the heck out of the brass. Progress is being made though. I just was coming in for the evening and my wife got called for a "girls night out". Woo Hoo, more shop time! Here's where we are now...

It's been pushed to the back burner, but I got a little time in the shop today. I did the gas tube mod and now am working out the FCG and smoothing the operation. I got the M60 spring. That will work better.

Mocked it up:

Your build is looking good! My opinion is that if you can keep the weight of the carrier mass down you will have plenty of bore pressure to cycle it. I would love to have one in .308 but I ran dry in that caliber and buying a case of ammo costs as much as the gun.

Making progress. I re-did the bolt, made the charging handle, the piston extension is done and it cycles well with the M-60 spring. The FCG is near done. Then it will all just be fitting and adjustments, beef up some of the welds and then on to primer popping.

So my wife fineally asked what I was doing in the shop so I explained it to her. Her only comment was, "That's how you are going to get yourself blown up."

I find her lack of faith disturbing.

Well, it shot, and didn't blow up. I was shooting it from a lead sled, and it doesn't have quite enough oomph to get all the way back. I was using surplus, so the loads were a little light, but my 1919 likes them. I'm going to mess with other loads and the gas ports, but this thing is gonna work! I got rained out before I could do much today.

VIDEO 404

How big is your gas port?

Thanks for posting the vid. You are ALMOST THERE! You cranked out your build in no time, and it looks great. We appreciate your sharing the pics as you went. Good luck with sealing the gas system - my gas ports for x39 are .191 which sounds large, but they've maintained accuracy. A little tweaking here and there is to be expected

My relief ports are about 1/2" ahead of the rear mosst position of the piston. I plan to weld them up, then re drill them at the absolute rear position. All I need is that last 1/2" or so.

S/S is correct. The bolt should be completely unlocked before the gas is allowed to bleed of.

Drilling a larger gas vent in the barrel may be the solution to the problem, but you probably should use that as a last resort. Try other means first, IMHO.

Thanks, yes, the gas doesn't bleed off until near the very back of the stroke, but i need to move it back that last bit to keep pressure up through the entire stroke. I may actually move to one and a smaller vent hole. I'd like it to work with the light surplus loads. I would rather not drill a larger port in the barrel if possible. There are other options too, muzzle booster etc. I am not considering a larger port at this time.

I got some more done and am nearly ready for the next range trip. I welded up the old holes and made one furthur back that should exhaust up, toward the barrel. I fabed up a front handguard that i will put rails and covers on, welded on a Krink style brake, charging handle, and put on some basic sights(AK front, SU-16 rear).

Here are the pics. It needs a LOT of clean up.

And here are the pics of the internals that I'm sure you have all been waiting for. It still needs a lot of clean up, but everything came from the llocal hardware store, small galvy pipe (3/16 I think) for the extention, rod for the pin, flat metal and angle iron. Very basic. I did weld a bunch, but if you are more patient than me, you could have avoided it.

I've got maybe $400 in it. I took it to the local indoor range today. It is SO close. It just needs to come back another 1/2 " or so. I'll tighten up the gas system some. I manually cycled about 20 rounds through it. Functions well and groups on paper. I'll make a video once it works!

Sounds like you can see the finish line, from where you're standing. And being the first one in .308 - you have broken new ground. I don't know how strong your recoil spring is (or what length) but my M60 springs have just enough strength/length to strip, chamber, and rotate the bolt shut. Only then would it work. I did alot of experimenting using several different length springs (it did incur extra cost) but the weakest/shortest ones worked best, in the end. I had to stack sections together (not ideal) after cutting it too short, then used a new full section, after the best length for function was determined.

Two questions, somewhat off-topic. How would you rate your build, as far as the entertainment/enjoyment/challenge factor? Meaning enjoying the construction process, the build challenges, and your anticipation level?? I think that's a fair question to be asking. Personally, on a scale of 10, I'd rate any beltfed AK a solid 12. Low cost might yield a 13

2nd one - Were you mentally saturated, to where you dreamed about it at night, throughout the process? I did during mine - alot. Thought about them almost nonstop, day and night for weeks on end.

Good luck getting that last half inch of travel. Tighter gas system, and lightened BC (made a huge difference here) and charging lever never hurts either. You could always (incrementally) enlarge the gas port, as a last resort.

So, I tightened the gas system and opened up the gas port to about .150 and went back to the range. It still does not quite get all the way through the cycle. It does fire, extract and sometimes eject, but because it doesn't get all the way back, there is not enough inertia going forward to strip the round and feed. Or at least i think that is what is happening. It fires and lockes up almost all the way back. I then can pull the bolt back the last little bit and it slams home, functioning properly the rest of the way. So, I came back, cut the back part of the spring into 3" segments so I can adjust it easier at the range and opened the gas port all the way to .189, per the plans from SS. I don't know when I'll get back to the range, but when I do I plan to video it to see where it is stopping if it does.

By the way, between the weight of the gun and the recoil being absorbed all by the spring, recoil is very mild for a .308.

I wonder if Fal springs would work?

Yes, the M60 spring is the right spring for sure, it is just a balance to get to go all the way back and fwd. I am really close, but won't get too the range for a few days so I'll just have to keep thinking about it.

On my original MG47 prototype I made a gas tube out of a section of a 12ga. barrel and a piston to fit. I did have to slightly open up the RSB to get the larger piston to pass through. Then with a very tight gas tube to gas block joint, I had just a little too much force. The BC would slam back into the butt stock, which was also the BC stop, with enough force that it started to egg out the butt stock attachment pin holes. I then drill some gas relief holes in the gas tube but it still gave me more that enough force to actuate the feed get full stroke from the BC and operate the feed cam. An adjustable gas block would be a nice feature.

Seal that gas system tight! 3/4 of the problems with all MG47's built to date have been insufficient pressure to cycle. Tighter the gas tube, the more likely it will work. I know!

Even the 12 ga gas tube did not work when I did not have a tight seal to the gas block. Once I made a very tight, no leakage at all seal, the gun cycled great and only after several hundred shots did it start to egg out the butt stock attachment holes. A rubber buffer stopped that and just to see what would happen, I drilled a gas relief hole about 1/2 in ahead of the rear most travel of the gas piston. I have build 3 MG47s now and all of them didn't work until I made a no leakage gas tube to gas block seal and a very close tolerance gas piston to gas tube fit.

CNTRAILRIDER and the other builders that have successfully got one to cycle have found the same thing. Granted, the 12ga diameter gas tube and piston was over kill, but once I got a no leakage tube to block fit and a no more than .005 thousands clearance piston to tube fit with a standard diameter piston and a tube that did not relieve the gas pressure until just in front of the rear most travel did I get reliable cycling. The ES and BP versions both use a standard AK piston but a very tight tube to gas block seal and a tight clearance piston to tube I.D. fit.

Yes I experienced some rear trunnion slamming, but that wasn't until after it finally functioned. That can be be tamed with a buffer, adjusting spring length, BC weight, etc. But it must live before it can be tamed. In other words, it must complete it's function first. That's the best I know how to explain it; not intended as a rude nor know-it-all rebuttal. By golly I'm just learning as I go!

Getting there. I rebuilt the gas system and now it is good and tight. I fired it and now it goes all the way back, but the extractor doesn't kick out the brass all the way so i have to make a slightly bigger and harden it. Then we should be good. I'll post a video as soon as it works reliably...

That was the beginning of when mine began working. W/O full stroke it's sort've pointless. You can always adjust spring length later to prevent the BC from slamming the rear. Rubber block or even an eraser makes an OK temporary buffer to prevent damage. Study the wear on it. Good Luck

It runs! And is fun. It still is not 100% , but it gets through about 9 out of 10 rounds in a 10 round belt. I loosened up the links a little and ran hot ammo and it was blasting! My friend shot a video, I will post it as soon as he sends it to me.

Woo-hoo, $400 belt fed .308.

I actually need to come up with a sling and bipod or something. The way I made it right now, you have to pull the bold to the rear when loading. That means you need one hand holding the bolt while the other places the belt and closes the top-cover. So, if you don't have the gun sitting on something, you need an extra hand to load it.

Try leaving the first 3 links empty and hook the first link on the little tab that projects to the right on the feed tray. Make sure that the feed cam is all the way to tlhe left and you should be able to close the top cover and latch it. Pull your cocking handle back and release it and it should advance and chamber a round. You might have to cock it twice to get it to feed, some work the first time and some seem to have to be cocked twice, like an M2HB.

I don't think that will work because I am using desintegrating links. I'll keep messing with it, but it is not much of a PITA. I am just glad it is running.

How did you finally configure the gas tube?