Is it possible to convert a Yugo M76 (8x57IS) to 6.5mm Swedish?

[Whats-his-name]

Howdo all,

I'll put this one out there, more for academic discussion than anything else.

I have a Yugo M76, a nice semi-auto 'sniper' rifle, for informal target shooting. As many of you know it fires the 8mm Mauser (8x57mm IS).

While this is a good round I've always liked the 6.5x55mm Swedish for obvious reasons (less recoil, more accurate, etc.). The cartridges are very similar in size give or take a little, with the total length being about the same (about 0.5 to 1mm [0.005 to 0.01"] shorter in the Swedish, depending on the bullet used).

I've always thought that it might be possible to convert the M76 to fire 6.5x55mm (if it can be done with a K98 then why not...).

Other than the obvious barrel change (with appropriate machining for the gas port and other bits), the only changes that appear to be required are possibly the reshaping of the extractor claw, possible opening up of the gas port a little, while the bolt face may need a very slight widening (by 0.25mm [0.001"]) overall if at all, to accomodate the very slightly wider base of the 6.5mm. Not sure about the magazine - the 6.5x55 round is very close to the 8x57mm in width (I think about 0.25mm [0.001"] slimmer at the rear and 0.1mm [0.004"] fatter at the front). The cartridge is shorter in the 6.5x55mm but its overall length is made up by the longer bullet. With this in mind, I'm guessing the magazine does not need to be modified but I stand to be corrected on this.

What do you lot think?

I'm probably missing something out and I'm very willing to be educated.

 

[WardenWolf]

A semi-auto gun is a completely different beast than a bolt action. The M76 is a gas-operated rifle. You'd need a new barrel with appropriately-placed and sized gas port, as well as a weaker mainspring calibrated for it. You'd also need a new magazine to feed it. You'd have to have a custom barrel made from scratch just for your gun, as well as several other custom parts. We're talking thousands of dollars to change a gun that previously cost less than a grand, and there's still no guarantee it will run reliably.

 

[justin22885]

it wouldnt cost thousands of dollars to convert one, the mauser magazines may even work for it, similar base diameter and taper, if not adapting other magazines to a custom AK build is not that difficult at all as it generally lacks a lower receiver

by far the most difficult part would be the barrel, but knowing just a few key specs and omitting the unnecessaries like the handguard retainer and front sight block makes it a lot easier.. there are no locking lugs to cut, no special surfaces, just make sure the blank is turned down to the right dimensions at a few key locations and turning one on a lathe is pretty straight forward

as for the gas system, 6.5x55 has slightly lower case capacity than 8mm mauser, but it has a smaller bore while pressures are still the same so actual gas pressures when the 6.5 reaches the gas port and the bolt thrust itself would be pretty close, it may work with the standard springs and the easiest solution to the gas port size is to drill it small and work your way up

 

[WardenWolf]

Justin, I'm sorry, but you're very wrong here.

One, gunsmiths aren't cheap, even for fairly simple work. This is heavy-duty custom work here. Even gunsmiths don't make their own barrels. They can turn down and work on others, but they don't make their own; they're too precise and the equipment needed to make them is too large and expensive. You'd have to contract a barrel manufacturer to make you one.

Two, for the gas system, it's not just pressure, it's volume. The AK is a long-stroke gas system. It needs a high volume of gas to function. A weaker spring would help tremendously, but remember that the spring still has to move that huge bolt carrier and get it to run over the hammer on return.

Three, the Mauser magazines may "work", but you'd still have to have a custom feed ramp. And if they don't, you'd have to have magazines custom-made or adapted. Also very expensive.

I'd guess this gun would probably cost upwards of $4000 to make work. Sure, it could be done if you throw enough money at it, but at what point do you say enough is enough?

 

[justin22885]

ive probably built more AKs than you will ever fire and $4,000 is absolutely an insane, baseless quote with absolutely nothing to go on but assumptions, having a barrel lathed to a custom contour only costs a couple hundred, magazines MAY work and if they do at the very most all youd need is to enlarge the gas port, thats a far cry from a $4000 price tag

and second of all, the gas that operates the AK does not fill the entire volume of the gas tube, it only fills the volume within the gas block, after a very short distance of travel the gasses are vented while momentum handles the rest.. it is not actually a true long stroke in the sense that the piston remains under pressure for the entire duration of travel, but operates more like a short stroke but with a fixed piston

 

[Scooter22]

Why don't you sell it and get a AG42? I'd think it would be cheaper all the way around and you don't hack up one rifle to make something you can get in another existing platform.

 

[barnbwt]

I have a Yugo M76, a nice semi-auto 'sniper' rifle, for informal target shooting. As many of you know it fires the 8mm Mauser (8x57mm IS).

They are nice . Like, really nice. Like, 1500$ for a built gun, nice. Enough that modding an existing version of this rather uncommon firearm is probably unwise.

However...parts kits are stupid cheap (compared to like a PSL) and still available, and there are a couple companies making receivers kicking around. Making a second gun would only cost the extra 400$ or so of the kit, plus another 400$ for the receiver or so. The barrel is pricey, but that's a fixed cost no matter how you proceed. Whether a second excellent rifle is worth $800 is up to you

As to the conversion itself;
-If the length is very close but shorter, no problem
-If the bolt face is that close, likely no rework of anything is required (they are a bit roomy to start with) and whatever is needed will not affect function.
-I'll bet the 6.5 is close enough as far as pressure curve to cycle the gun as-is with an appropriately sized gas port (start small & work up). The M76 has a very unique gas system compared to most AKs which actually serves to lengthen/dampen the pressure impulse for more reliable performance across ammo types (gas goes through a metering cup, into the side of the piston head, out the front of the piston head into an expansion/venting chamber)
-Magazine is the biggest issue, as the stacking geometry will be different if the taper is off; I'd either try to find an AG42 magazine, or even better, use one of many 6.5x55 bolt-rifle mags with feed lips built in (I think SAKOs are). Another option is to use an MG15 magazine with straighter/narrower profile which may be more forgiving. All this assumes the rounds are different enough not to feed (which I wonder about, examining the two)

Why don't you sell it and get a AG42? I'd think it would be cheaper all the way around

Yes, but hardly cheap. AG42s are rather pricey, anymore. Granted, so is quality 8mm vs 6.5x55, so I say the conversion (from a kit) makes as much sense as a build in Mauser.

As far as the barrel; probably not as hard to source as you'd think. Hang around the gun building websites, and you'll find some talented folks who'll do a great job turning a blank to the proper journal size & chamber it. At that point, installing the thing is fairly straightforward for most gunsmiths. Price could easily reach into the thousands between a ~500$ blank and pricey well-known shops with fast turnaround time, but it could also easily be a hundred or so over the barrel blank price for the same thing if you 'know a guy' and can wait a little while.

Very cool idea, by the way; I had no idea the case heads were so similar, it really makes for a more effective rifle chambering at the end of the day. Even in 8mm the gun is a bit of a pussycat, so you should be able to watch your bullet hit in 6.5!

Another important advantage of doing a fresh build off a kit is that there is no advantage in keeping anything original. I'll be honest, the AK design kind of sucks for accuracy by virtue of how things are put together forward of the trunnion. Free of constraints to look original, you could more easily 'float' the barrel, as well as attach better sights, as well as better grips/stocks, without much additional effort or cost. End up with a PSG-1 type rifle vs a scoped battle rifle, which I assume is the actual goal seeing as the cartridge is something as long-ranged as 6.5x55 in the first place.

One last thought; a non-traditional build could even save you a bundle on the receiver-side. Milled receivers are at least 400$ on a good day, but a kit that has the forward trunnion with complete locking lugs intact (or a PSL trunnion, since I'm thinking they are sufficiently similar up there) can be mated to a standard sheet metal box receiver like a PSL and reinforced as desired for more rigidity. Not as 'factory' as the original guns, but potentially half the cost and equal quality & effectiveness (or more, if the AK trigger group holes are replaced with a standard AR15 pattern so a Geissele can be plopped in)

-Parts kit, 450$
-Receiver, 250$-450$ (if you can MIG weld, maybe 100$)
-Barrel, 300$-500$ (a Green Mountain blank is only 100$, if a 'bargain brand' is sufficient to your tastes)
-Magazine, 50$, if actually required which I kinda doubt
-Labor, say 4hrs for the barrel & 4hrs for its installation/assembly into a rifle

I'd bank on 1000$ budget as a target to do a kit build, and about half that for modification of the existing rifle. And about six months' time, whoever does the work; unless it goes magically well, some debugging/rework will be required, so six months is reasonable unless your smith has zero backlog (likely because he's terrible in the first place )

TCB

 

[barnbwt]

ive probably built more AKs than you will ever fire and $4,000 is absolutely an insane, baseless quote with absolutely nothing to go on but assumptions, having a barrel lathed to a custom contour only costs a couple hundred, magazines MAY work and if they do at the very most all youd need is to enlarge the gas port, thats a far cry from a $4000 price tag

From a fancy pants famous smith like Red Jacket :yuk: or something, and the requirement it be delivered in a mere two weeks or something, yeah I could see it costing that much. Otherwise, no, unless you let a smith/conman give you the runaround & waste your time/money building six rifles before delivering one. A very nice match barrel blank, turned & chambered at similar quality could easily run over a thousand --we see it all the time in the bolt action crowd, and in 6.5x55 no less-- but the remaining build is going to be very much standard-OP AK build no matter what you do. Lapping & squaring the chamber would be a drop in the bucket compared to the barrel cost, and would probably yield near-ideal accuracy for the AK platform (there's obviously limits at the end of the day). Stiffening the action & using a heavy profile barrel would probably bring it up near to the same level of accuracy as any quality autoloader.

I could see blowing 2000$, maybe 2500$ on a kit-build provided only the best was allowed, 4000$ if you also absolutely had to have someone build an entire receiver on CNC for you instead of a much more practical alternative.

TCB

 

[MikeInOr]

I am a big 6.5x55 fan. I think it is an excellent cartridge and one of the best battle cartridges ever conceived. I have several Sweeds including a AG42 Ljungman. The AG42 is a beautiful long weapon that is fun to shoot and mine is very accurate. It is very different than the Dragnov/AK receiver and I personally like it much better. I wouldn't butcher a perfectly fine M76 to convert it to a bastard... that is what AR10's are for.

Can it be done? Sure, almost anything can be done. But by the time it is finished and functioning properly with all the bugs worked out it is not going to be cheap... you are going to be very close to building a whole new gun from scratch. I guarantee Kalashnikov's first prototype didn't function anywhere near perfectly. Sure, it is easy enough to take existing parts and clone an AK but you are talking about creating a whole new gun... A prototype in essence.

I don't like the big old 8x57 near as much as I like the 6.5x55 but a lot of that is due to the very low levels 8x57's are loaded to in this country. Maybe if you tried working up some hand loads for your M76 you might find a whole new appreciation for it?

 

[Whats-his-name]

Hi all,

Thanks for the replies - very interesting and differing views and all appreciated.

In answer to those who think I might be considering an actual conversion - don't get me wrong . Although I'm also a machinist and have made gun parts, including an 18" barrel (which actually worked quite well), I don't propose to mess around with the rifle, it's too nice for that. If I wanted a 6.5x55mm (which would be nice) I'd buy a bolt-action like a Sako or some-such rather than try a conversion of a semi-auto. The M76 in my possession I got cheap (350 Euros) from a friend and is part of the reason I have it.

I just wanted to understand the process required for such a conversion if it was indeed possible.

It would also be interesting to see if a conversion could be made without actually harming the rifle, i.e., change, rather than machine, the parts that can be changed (bolt, extractor, mainspring, barrel, possibly magazine) without 'permanently' changing it to a 6.5mm.

...in 6.5x55mm I'm sure it would make an interesting sniper rifle but that would be getting off-thread!

But as I said in the opening post I ask out of academic interest in the hope of learning something, particularly about the more subtle but just as important aspects of such work.

Maybe, as and when the barrel dies, I might consider a rebuild but that will be a few years off. It could be an interesting experiment. In Europe (where I am) M76's aren't uncommon and certainly a little more common than in the US so converting one that is 'used' shall we say isn't too much of a moral dilemna as there will be plenty of others around.

 

[barnbwt]

One, gunsmiths aren't cheap, even for fairly simple work. This is heavy-duty custom work here. Even gunsmiths don't make their own barrels. They can turn down and work on others, but they don't make their own; they're too precise and the equipment needed to make them is too large and expensive. You'd have to contract a barrel manufacturer to make you one.
Dude, all you need is a decent lathe. Heck, I have a bad lathe and am able to turn down & chamber barrels, though less efficiently than a proper setup. There are "gunsmiths," and there are gunsmiths (and Bubbas); if you choose the former, he will farm your job out to a real machinist for a premium & both guys will take a cut, the latter will do it for cost + labor. A lot of "gunsmiths" make their bread bore-sighting scopes and assembling ARs, anymore; it'd make more sense to look for a machine shop to make/chamber the barrel than a smith to be honest, since all the FFL complication does not apply and you're likely to get more competent/timely service. Barrel blanks range from one to several hundred dollars for the most part in 6.5mm, and it isn't until you try buying ready-made chambered/profiled/finished stuff from premium makers (which won't be available for an M76) that the parts get pricey. Check out Green Mountain sometime, and open a world of possibilities for yourself; they are one of few blank-makers that bother to sell to the public

Two, for the gas system, it's not just pressure, it's volume. The AK is a long-stroke gas system. It needs a high volume of gas to function. A weaker spring would help tremendously, but remember that the spring still has to move that huge bolt carrier and get it to run over the hammer on return.
The M76 has a special gas system that I suspects works primarily to dampen the pressure curve (it essentially makes the gas system 'longer' and skinnier) which would potentially make it more adaptable. Might explain how OOW is making 308 & 30-06 versions with standard parts & a barrel-swap. The M76 gas system is also adjustable, which may be helpful for tuning (and the regulator an easy part to make/modify)

Three, the Mauser magazines may "work", but you'd still have to have a custom feed ramp. And if they don't, you'd have to have magazines custom-made or adapted. Also very expensive.
Fair enough, but it's not like the original mags were the peak of reliability, either . Feed ramps are Dremel work; tedious, but not expensive, and it's highly likely the original is good enough (might actually work better without one, since the 6.5 bullet is so long it may enter the chamber before the round clears the feed lips; the 8mm's only sort of need the thing for the same reason

TCB

 

[barnbwt]

The M76 in my possession I got cheap (350 Euros) from a friend and is part of the reason I have it.

Ooooh, this changes things quite a lot;

-In the US, there are no 'original' M76s, as they have the auto/safety sear which by our rules makes them machineguns & illegal for import. All got torched/rebuilt from scrap, so are few & far between, which makes them very valuable/rare. Overseas, not so much; I understand the Ukrainian & Syrian conflicts are lousy with them, and dummy guns are common across Europe with little or no molestation beyond the barrel & maybe bolt face
-Barrels will be the hard part for you, as that is what's regulated overseas for the most part. I know Lothar Walther makes nice blanks in 6.5, as does SAKO and others, but I'm not sure how import/export rules affect your ability to get them, and licensing your ability to have a machinist/gunsmith turn one to your specs.
-If the bolts you have access to are all destroyed, you may be in a tight spot; that's a part that can't be easily made for a reasonable price, and won't be found separate from a complete gun if it's considered contraband in the wrong hands over there. In the US, only the receiver is so controlled, so 'parts kits' with all the other small items are freely available. It may be possible to source one through a properly licensed source for a reasonable price, though.

It would also be interesting to see if a conversion could be made without actually harming the rifle, i.e., change, rather than machine, the parts that can be changed (bolt, extractor, mainspring, barrel, possibly magazine) without permanently changing it to a 6.5mm.

The AK-style design has the barrel force-pressed into the receiver journal and pinned in place with a press-fit pin; changing back and forth is only somewhat plausible with a lot of work (and potential of damaging the journal/barrel surfaces). Honestly, it sounds like the barrel alone may be all that is required, and provided the receiver & bolts are available (or completely unavailable apart from your rifle's) would make more sense to replace than building a complete rifle unless you desire both chamberings. Sadly, you won't be able to export the barrel over to the US where it would sell for the better part of 1000$ ('assault weapon' barrels got banned from import by George II's first reign)

The conversion itself is quite doable, and probably quite affordable if you can make the barrel yourself; you'd just be buying a blank, then pressing out the old barrel/pin, and pressing in the new one before reassembling. Couple hundred euros and a few weekends, assuming the logistics are there.

TCB

 

[Jim Watson]

Considering the wide variety of 8mm ammo that your Yugo presumably will shoot, I think it will run on 6.5 without too many changes.

I'd put an 8mm in the chamber and some 6.5s in the magazine.
Pull trigger. Now, where is the 6.5?
In the chamber? Great, but don't pull the trigger again.
Jammed up? Time to do some hard thinking before going ahead. Modifying or replacing the mag could be the hardest possible change.

All the barrel takes is the work. Not like .264" barrels and Swede reamers are hard to get.

Mainspring? Does he mean recoil spring? That is way down the road.

 

[justin22885]

Considering the wide variety of 8mm ammo that your Yugo presumably will shoot, I think it will run on 6.5 without too many changes.

I'd put an 8mm in the chamber and some 6.5s in the magazine.
Pull trigger. Now, where is the 6.5?
In the chamber? Great, but don't pull the trigger again.
Jammed up? Time to do some hard thinking before going ahead. Modifying or replacing the mag could be the hardest possible change.

All the barrel takes is the work. Not like .264" barrels and Swede reamers are hard to get.

Mainspring? Does he mean recoil spring? That is way down the road.

definitely a good idea to start with the mags, see if 6.5x55 will feed from them properly.. if not then your biggest obstacle will be finding magazines that do, the barrels the easy part

the OP could achieve the same ballistics in 6.5 creedmore though that would only require a barrel swap on a yugo M77, saiga 308 or vepr so unless he SPECIFICALLY wants 6.5x55 for whatever reason, looking at creedmore, 260 remington, or 6.5x47 might be better

 

[WardenWolf]

An AK indexes off the case shoulder when it feeds. Then it noses the bullet into the breach and uses the tapered case to get it aligned and centered.

Here we have, from left to right:

9.3×62mm
.30-06 Springfield
7.92×57mm Mauser
6.5×55mm
.308 Winchester



8mm Mauser is in center, with 6.5 Swede directly to the right. The Swede's shoulder is farther back, and has a much more gradual angle, while the overall length of the round is very similar. What this means is that the round will travel farther fowards before it begins to angle up into the bore. Most likely this will result in it striking the lower face of the breach instead of feeding, or if it does feed it will feed roughly and chew up the bullet. It's possible that modifying the feed ramp will fix this, but most likely the magazine will need to be modified as well.

This an iffy conversion. You'll need an oversized barrel, then it will need to be turned down and a gas port drilled. The resulting barrel will be very heavy due to being oversized, similar to a Saiga .223 which uses an underbored 7.62x39 barrel. That said, the extra thickness of the barrel wall will contribute to rigidity and accuracy.

I think it can be made to work, if you put enough money into it. But because of all the custom work involved it's not going to be cheap.

 

[yugorpk]

Its not that difficult to thread and chamber the new barrel. It will need to be cut from a fat blank as standard bolt rifle contoured blanks will be all wrong for the fat M76 gas block. Any gunsmith worth his salt can cut the barrel threads and chamber ream for the swede 6.5. Have him countour it for the gas block and set up the headspacing and cut the extractor relief and finish the rest of the work yourself. Ive owned a few M76's and they really arent that exotic to the point where the 6.5 conversion would take thousands of dollars to complete. 4 hours of shop rate..

 

[justin22885]

you have to have the barrel contoured for the rear sight block as well, without it you have no means to hold on your gas tube nor your dust cover, and if you want to use the original handguards it will need to be contoured for the handguard retainer as well so there are four key points it needs to be turned down to a specific diameter, the chamber, the shelf for the rear sight block, shelf for the handguard retainer, and the shelf for the gas block

here is a CAD drawing of the yugo M76 barrel showing you the location and diameter at each location to properly contour an M76 barrel, give this to whoever you have contouring your .264" blank and they should be able to do it

http://robertforbus.com/Barrels/yugoslavian_m76_7,92x57.pdf

 

[Whats-his-name]

Thanks everyone! THR at its best.

I'm beginning to think of looking around for a ratty(ish) M76 to see what can feasibly be done now - more as an experiment to satisfy my curiosity. It won't be for a while but I'll pass on any information that results from it (positive or negative). In the meantime I'll need to thoroughly educate myself on design and function (which is an interesting exercise in its own right).

...and thanks Justin for the PDF - very useful!

 

[CB900F]

What's-his-name;

I certainly understand the curiosity factor, the hmmm-what-if-edness about it, but sheer practicality leads me to ask: Why not just go for the Ljungman?

900F (That's a Fireblade to you)

 

[justin22885]

shear practicality asks me why not take an M77, saiga .308, or vepr 308 and convert it to 6.5 creedmore, definitely no mag fitting or feeding issues there, only a barrel swap and the performance is the same as 6.5x55

 

[Whats-his-name]

Howdo all,

Thanks for all your input and time - it has been very much appreciated.

Did a bit more research and I had clearly overlooked the obvious - the 6.5x57mm Mauser - a necked down 8x57/7x57mm. Therefore, all that would be needed is a barrel change. It would have the same characteristics as the 6.5x55mm SE as the bullet weight and loads are pretty much the same.

I haven't had a good look around yet but bullet selection looks limited compared with the Swede and presumably I'll need to make sure the case head is man enough for the more vigourous extraction of the M76 - it should be as the dimensions of the case head are exactly the same as its Daddy.

More research to be done...

Cheers,

 

[justin22885]

try the 6.5x55 in the mag, if the feed lips hold the cartridges at the proper angle and they feed properly then theres no reason really to not just go with that

 

[Whats-his-name]

Thanks Justin,

Yes, absolutely. I'll be borrowing some to see if they do go as going with the 6.5x55mm will give me more bullet choice but at least I know I'll have the 6.5x57mm to fall back on if all fails.