View Full Version : MG47-308
10-18-2008, 10:34 AM
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 particulagly 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?
Fritz needs his password!
10-18-2008, 02:07 PM
If you are any good at reaming barrels, and promise to return a reamer in the condition it was lent, I have an extra 308 reamer i'll loan you for shipping costs.
currently logged in under a temporary ID
(Still need my password!)
10-18-2008, 04:06 PM
Well, thanks for the offer, but I have yet to ream a chamber, so I would have to either send out the barrel, or abide by the "you break it, you buy it" policy (which I most certainly would). Either way, I am looking at late December at the soonest to get started. What brand are you using and what do you think of them?
Fritz needs his password!
10-18-2008, 11:03 PM
I have used several reamers from different manufacturers, and haven't had a really bad one yet. Because of my lack of negative experiences in chambering barrels I cannot really say that i dislike any one brand.
When it comes time to do it, if you decide to have it done by somebody else, give me a shout.
10-19-2008, 12:05 PM
Thanks, I will probbably take you up on that offer. As for the rest of the project, I see very little that will have to change from SS's original design. I'llbe doing it with spade grips (it's a CA thing) I am thinking:
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.
10-19-2008, 12:58 PM
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.
Thoughts? Has anyone tried this yet?
FOR THE RECORD, I'll say that a .308 barrel should be used. Not sure how well that will run , but others with more experience in that may have a different opinion. The effects on accuracy are questionable.
Another "FOR THE RECORD" - my .308 build shoots custom loads that are loaded primarily for accuracy. These loads are lighter than factory surplus ammo. I would say that all of this surplus ammo people are buying would be too hot for my build, and I would not recommend it for other builds. Did the Yugo 308 builds have the same bolt? Yes. Is this a Yugo RPK? That would be the best place to start because visually the bolts are identical.
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
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.
Moral of the story -
1. Pookie recommends a .308 barrel for .308 bullets.
2. "IF YOU MUST" - Pookie recommends drilling extra gas ports in the gas tube.
3. Welds have no place on an AK receiver. Use a milled receiver if you want extra strength. Or reinforcement bars like HK did on their short-lived HK-21 model.
4. Pookie recommends caution - you are pushing really high pressures with a .308 and I would not want to see you blow parts of the kit into your face!!!
10-19-2008, 02:10 PM
THANKS A LOT FOR THE INPUT!
That is what I am thinking about and discussing here before I get started.
Yes, it is a Yugo "finned" RPK kit with the "bigger" bolt and bulged trunion.
I planned on doing exactly what you are saying on the ported gas tube. I was actually thinking of drilling several holes in it (what is the hole setup you used to get yours finctioning properly?) and then sleeving the gas tube with a sleeve that slid over the ports to be adjustable so i can start with the most holes and least gas inpulse, then slide the sleeve over it to get to the right combination of gas venting and impulse to operate the gun.
As for the chamber reaming, that is why I am looking for someone who has done it. I heard a few folks mentioning doing it, but I couldn't find the updates (that might be a bad sign) I REALLY want to use that big, fat Yugo finned RPK barrel though. it is one of the coolest looking barrels out there.
And on the ammo, yes, I shooot my own reloads that I load light anyway. Still in the research/brainstorming phase though. Thanks again for any input.
10-19-2008, 03:02 PM
It is using one of the YUGO RPK kits like this one with the big heavy barrel. (Photo shamelessly stolen from a gunbroker ad, but I bought two of these from this guy, so I doubt he'll mind).
10-22-2008, 10:04 AM
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.
10-22-2008, 10:49 AM
Thanks, I had re-thought that after my original post, but never edited it. I think once I get it going I will replace most of the screws with rivets/ weld to get the strongest reciever possible. I'll still keep some as screws for tweaking/ replacement etc. My whole thought process is ensuring that if there is a chatostrophic failure it goes up, through the top cover. The only ones I have seen personally were on M2 and due to headspace issues and that shouldn't be a problem with this. Really, I can't see any way, if you do it right, that this could be any more prone to disaster than a standard 308 SA rifle.
I am still looking for someone that has successfully re-chambered a x39 RPK barrel for .308. The lack of response leads me to believe that either it is a briliant, cutting edge idea, or those that have, are currently no longer able to type.
Either way, after the Wife and the Dogs, I miss my shop horribly.:bye2:
10-22-2008, 01:05 PM
I had a Romak that had the case separate at the base because the bolt was not fully rotated when fired, resulting in excessive head space. The hammer was not the stock shape and didn't hit the projection on the back of the bolt carrier that it is suppose to stop the hammer from hitting the firing pin if the bolt carrier is not fully forward. It had a 1.5mm receiver and nothing more happened than it blew the top cover off. It wasn't my gun and I was given Bulgarian yellow tip Maxim high pressure 7.62x54R ammo to shoot, which should never be shot in a AK variant.
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"-16tpi, 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.
10-22-2008, 03:53 PM
I don't know the actual size, but the gas hole in my Saiga .308 barrel is about that of the wire in a 1 1/2 inch paper clip. Not very big at all. I don't even have a drill bite that small.
10-23-2008, 03:40 AM
Thanks again for all of the good info.
12-03-2008, 01:38 PM
I'm back and beginning this project if you still are still willing to loan out your reamer or ream a chamber-John
12-13-2008, 12:55 AM
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???
12-13-2008, 10:39 AM
I'm going to be following your project. I wanted to do one in .308 but the ammo prices nixed it. Looking good. I hope you keep posting pics as you go
Steve in El Paso
12-13-2008, 11:18 AM
Looks real good so far. Keep going the way you are and you will have a great build. Don't hesitate to ask for advice from those who have built a MG47. One in 308 will be very nice.
P.S. Glad to see you got back safely.
12-13-2008, 01:31 PM
Thanks for all the help guys. I hope I can pull it off. It will be a slow one though. Today, I will be finishing drywalling the new bathroom! My wife is not keen on the idea of gun-ports in the shower. I wanted armor plate in the walls, but she wanted conventional insulation. She is such a buzz kill.
12-13-2008, 08:15 PM
I'll be keeping track of your build as well. I have been wanting to do such a build for years. Lord knows how long that parts kit will set in the box. It has been three years so far.
12-23-2008, 03:33 AM
Well, the reciever's slapped together. I got all of the drilling and tapping done, but left it the full length of the 24" bars. I figured I will have to lengthen it about 12mm so now I can cut it later. I used tan paint for the layout, that's why it's yellow looking.
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.
12-23-2008, 09:28 AM
Very cool and good start.
(I really like your combination carry handle/top cover pivot pin. Very clever) Just kidding.
12-23-2008, 03:32 PM
I really like your combination carry handle/top cover pivot pin. Very clever
Yea, that's pretty cutting edge stuff. You can add it into the original design if you want, but I demand it be named the "Mustang Handle"
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.
12-23-2008, 05:14 PM
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.
12-23-2008, 05:34 PM
Thanks. I'll play around some with it
12-23-2008, 07:00 PM
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.
Real nice pictures - keep us posted