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MY SONS SWITCH BARREL AK BUILD IDEAS

16K views 114 replies 24 participants last post by  twa2471 
#1 ·
Im starting a build for my son and he got a box of AK parts and barrels and stuff for Xmas. it will be a 243 0r 260 remington loaded to light pressure.
Its going to be a light weight sporter and I want it as light as i can make it besides the heavy m70 trunion. this will be a outside the box build over the next year were he helps build it. He is 9 and will be able to shoot deer next season. I plan on letting him do as much on it as he can including some of the machine work that way he will know whats going on and how it all works and get some Shop time with Dad. It will have gas shut off as well and he will be shooting this as a non semi auto at first. Baby steps here.

Hes pretty sharp and noticed I had three barrels in the box, a 243, Win 260 Remington and 308 WIn there all model 700 take offs. he asked why there were three barels and I told him we were only going to use one but I hadent decided what one and that id keep the other two. Well hes not one to give stuff back that he just got, so he says way not use them all and just change them.

I have thought of several differant switch barrel assembly set up's in the past but they all required seperate trunions on a screw build. So got to thinking about a threaded barrel set up.


it looks like a 1"-12 thread can be used on the 23mm trunion if the bore is opend up to .9219"
that is .016 more than the factory bore. thats not much metal to get things right with with the boring bar if it dont cut good on the first try. the Yugo bore is not interupted like other trunions were there are hollow spots between the barrel and the trunion. aside from the barrel pin there is no interuptions. I really wish I had a virgin trunion to work with. the RSB will need to be removable or able to slide forward or you will not be able to unscrew the barrel. I was thinking of useing a barrel nut like the savage bolt actions and all barrels will need to be timed but that should not be a issue as once there head spaced correctly they will always be reinstalled in the same place every time.

I have seen were a guy threaded a 410 Saiga in conversion to a 500 S&W so I know it can be done. I think the model 70 Win uses a 1" thread .

this build is going to have a custom Aluminum RSB and likely a GB so I a dont have to worry about traditional looks in fact the less it looks like a AK the better for this build. people get nervious with kids shooting AK,s for some reason LOL.

I was even thinking with a differant bolt I could even do a 410 SG barrel for it.
 
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#33 ·
HMMMMM the fluted barrel will not work well with a 7/8 barrel nut because I have to thread from the muzzel toward the breach for the smaller threads and the Od of the barrel is larger than 7/8" for quite a ways this would require me to turn almost half the barrel down and Im not willing to mess up a nice expensive barrel like this that much, so it will need a barrel nut the size of the trunion threads that can go on from the back. On a standard barrel its still a viable option. HMMMMMM This might end up being a 300 wsm on a Saiga 308 action or at least a 308 WIN.

a custom nut can be made and i have seen some stuff on gocart axels as well that is cool ill figure it out
 
#34 · (Edited)
Why does the nut have to start on from the muzzle end? You could thread the breech end just enough to fit the barrel in the trunnion plus some room for the nut in front of it. Then just thread the nut on first and screw the barrel into the trunnion. After you set your head space, tighten the nut against the trunnion. That way you're only threading a minimal portion of the barrel over the chamber and not out onto the flutes.

Also, if you leave an unthreaded recessed shoulder on the front side of the nut you could hide the end of the threads on the barrel. Just make the ID of the shoulder a few thousandths larger than the OD of the uncut barrel just ahead of the threads. The fluting would still be intact and you'd also have no threads showing.

EDIT: something like this...
 
#35 ·
There's an article in the Dec 10 (14 if news stand) by Coffield where he makes a switchbarrel mauser using a savage type barrel nut. Its pretty much what GoMopar440 has posted. He used a die to extend the threads on the barrel for a barrel nut so he wouldn't have to time the lathe to the threads already on the barrels.
 
#36 ·
Why does the nut have to start on from the muzzle end?
because on a remington take off like I want to use the thread size is 1 1/16 an after you put a nut on it you will be into the area were the gas tube needs to go with the nut. If I want to use a 1 1/16 tread for the trunion and a 7/8 for the the lock nut it has to go on from the muzzel end because 7/8's is smaller than 1 1/16". that means every thing from the muzzel to the 1 1/16" threads has to be smaller than 7/8" that means on the barrel I have Id have to turn almost 1/2 of it down. thats not going to happen On a $400 Krieger SS fluted barrel, Im keeping it as large a OD as possable to maintain accuracy and no way in hell Im turning half of it away.

the other problem is if you use a Remington or other take off barrel and have to cut the chamber off to rechamber to someting else, on a standard profile by the time you make the cut there is not enough room for 1 1/16 threads to be long enough for a nut at the barrel OD is now to small that far forward. the option is turn off the 1 1/16 threads and go with a 1" thread size that is just slighly bigger than the trunion bore. I havent turned the treads off a Rem 700 barrel to see if there is still 1" Left after the threads are gone.

I want to maintain the 1 1/16" thread size iff possable because all I have to do is turn the are past the threads down and then run a tap in on the original threads and just cut about 1" longer. A barrel nut on a 1 1/16 thread is going to be into a factory gas tube likely. I want to also be able to run heavy target barrels and 7/8" past the nut is to small.

I can run a big barrel nut but Im trying to make this workable on a standard hand guard slightly modifed RSB builds as well.

the other option is a 22mm trunion using 24mm threads and then there is more room for a nut. The down side is You dont have the stronger bulged Yugo trunion then for Higher pressure builds.
 
#38 ·
It doesn't. Unless you're just a glutton for punishment. LOL!

Seriously though. There is no reason I can think of for you to thread it on from the muzzle end.

Ok lets try this again re read my post below



because on a remington take off like I want to use the thread size is 1 1/16 an after you put a nut on it you will be into the area were the gas tube needs to go with the nut. If I want to use a 1 1/16 tread for the trunion and a 7/8 for the the lock nut it has to go on from the muzzel end because 7/8's is smaller than 1 1/16".
NOW IF YOU HAVE SOME WAY TO GET A 7/8 TAP OVER A 1 1/16" THREADED BARREL STUB IM ALL EARS. SHORT OF A TWO PIECE DIE tHAT I HAVE NEVER SEEN AND A TWO PIECE NUT I CANT THINK OF A WAY TO DO IT. I CAN CUT THE TREADS ON A LATHE BUT iD STILL NEED A TWO PIECE NUT OR ONE END OF THE BARREL OR OTHER IS GOING TO NEED TO BE SMALLER THAN 7/8" TO SLIDE THE NUT ON .

ITS KING OF LIKE THAT TOU WHE HAD WHEN WE WERE KIDS WERE WE STUCK ALL THE DIFFERANT SIZED AND SHAPED PARTS THROUGH THE CORRECT HOLE. THE BIG ROUND PART WOULD NOT FIT THROUGH THE SMALL ROUND HOLE :)



If I want to use a 7/8 nut for the jam nut and the reciver thread is 1" or 1/1/6" your going to have one hell of a time getting a 7/8 tap over a 1" or bigger barrel stub.

If I was using a nut the same size as the trunion threads then yes it will go on from the back.

the problem with your picture is the barrel will get smaller after the trunion threads not bigger. especilay if you cut of the end and rechamber. I can barely get enough diamaiter for the trunion threads as it is. If you start with a blank or a heavy varmint barrel you can rechamber and extend the the threads of the same OD far enough forward for the nut. how ever the nut will be to big for a factoy gas tube and hand guards and will stick past the reciver.

Im going to turn the threads off a Rem 700 barrel and see at what diamiter they clean up. If I can get 1" then Ill just cut the threads off all my barrel and go with a 1" thread and possably a 1" nut and let it ectend past the reciver I wont be using factory grips any way.


in your picture the area maked unthreaed needs to be smaller OD then the threaded section. This nesatates putting the nut on from the front.

If you use a 7/8 nut and a larger trunin thread every thing forward from the the jam nut threads must be smaller than 7/8"

also if your using a 23mm trunion 1" is likely the smallest thread that will work. with a
1 1/4" wide reciver that only leaves 1/16 if a inch if you want to keep the nut inside the reciver width. on a 1 1/6 thread its next to nothing. so that leaves out fctory hand guards. not to mention the nut will hit the Gas tube slot on the RSB.

In the picture it shows how far Id have to turn the barrel down on a standard remington barrel to get the nut back to were it would work. also note were the slot for the Gas tube is in regards to the diamiter of a 1 1/16" barrel. On the fluted barrel I have (not pictured) the OD is even larger so id have to turn down almost half the length of the barrel to use a 7/8 nut.

On a normal AK profile this is not a issue just reduce to 7/8 in front of the larger trunion threads and thread from the front. the barrel will allow the nut to go all the way back no problem it only a issue if you want a heaiver barrel Like I do on some of the barrels I want use.

Im really hoping I can get 1" out of the barrels I have once the threads are cut off. the tap is cheaper as well.

In a standard 7.62x39,223, 5,45 and some of the lower pressure rounds like possably the 300 savage or 444 rimless marlin were a non Yugo trunion is considerd safe a 22mm trunion is ideal as it should not require boring and should be able to be taped with a m24-2,00 thread and nut would clear better and you would also have more room on a stock take off barrel to thread as the the ID will be smaller meaning you can go further down the barrel before the OD is to small. It would be much easier to do. A 19mm trunion would be sweet if they were avaliable any were then a 23mm factory barrel could be threaded and employed as well.
 

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#39 ·
I guess I'm missing something. The way I'm envisioning it I'd thread the nut onto the barrel at the breech end. Turn it on, advancing it toward the muzzle until it contacts the thread shoulder.

Turn the barrel/nut combo into the threaded trunnion, advance/retreat until headspace is set, then tighten the nut against the trunnion. Re-check headspace and if still correct, make witness marks on trunnion and barrel for future headspacing and retiming.
 
#41 ·
I guess I'm missing something. The way I'm envisioning it I'd thread the nut onto the barrel at the breech end. Turn it on, advancing it toward the muzzle until it contacts the thread shoulder.

Turn the barrel/nut combo into the threaded trunnion, advance/retreat until headspace is set, then tighten the nut against the trunnion. Re-check headspace and if still correct, make witness marks on trunnion and barrel for future headspacing and retiming.
that would work if I used a nut the same size or bigger than the trunion threads. every thing else would be the same as you described. except the smaller nut would still go against the trunion. it just goes on from the front and stays with the barrel with the Gb installed. this will you to reduce the profile and also use all the take off barrels out there that can be rechambered.

here some picks how it looks on a a trunion with a nut it still locks on the trunion face just the nut threads are smaller ID to take advantage of the profile reducing on many barrels and to allow a nut to clear the RSB as well allow modifed factry hand guards to fit.

got to think out side the box guys :) HMMMMM a OTB47 swithbarrel rifle would be a good name
 

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#42 ·
I have a idea for a way to eleminate the nut that Im keeping to myself untill I can test it I may try to market it and if it works It will be slick and would allow a barrel to be changed in about 30 It still will require threads on the barrle and trunion but will not regure any weird mods to any thing and would not look weird. Ive told one member to document my idea. If it works it will be easy to copy by the home builder.
 
#43 ·
OK, gotcha. You want to keep a lot of meat in the chamber area while using a small nut to cinch the barrel to the trunnion. Not so much thinking out of the box as not understanding the goal.

Sounds like a plan on your barrel-fixing device. Hope it works!
 
#44 ·
I see where youre coming from now. I missed the previous part about stepping the barrel with two different therad sizes.

What about switching the barrel parts (RSB & GB) out with larger Yugo M72 pieces?
Thats what I figured

the trunion in the picture is a m72 B2 and it is waht Im going to use on a the 300 savage and likley most of these builds. Ill be putting a 243, 260, 7mm-08, 308 and other barrels like 35 remington, 444 rimless marlin wild cat. grendel, 22-250, on a a bulged yugo rtrunion and hand all these at safe pressures .Im also looking at doing the same to my 308 Saiga and using a 300 wsm and 270 wsm barrel 6.5mm285 to lighter pressures and the barrels mentiond above and many more. on the 308 SAGIA the others can be loaded to 63,000 at least. my is one gun and a dozen barrels for any application as well as a 410 Shotgun barrel possably. hell might even do a 7.62x25 as well for it.


The 22 mm trunion in the AK74 is ideal for a 24mm thread and would need no boring to thread (I think)
 
#45 ·
OK, gotcha. You want to keep a lot of meat in the chamber area while using a small nut to cinch the barrel to the trunnion. Not so much thinking out of the box as not understanding the goal.

Sounds like a plan on your barrel-fixing device. Hope it works!
not so much wayout side the box just a bunch of new ideas and processes to build a rifle. I meant no insult to any one BTW. I wish i could draw on the computer to illistrate my ideas.

This stuff better work I got close to a grand in parts and barrels and tooling tied up in making this happen. The entire gun will be way out side side the box when done besides there will likely be no part un modifed in some way Im hoping to put every thing have into this one. Im thinking engine turned stainless reciver possably. and a bunch of other trick stuff.
 
#46 ·
What about switching the barrel parts (RSB & GB) out with larger Yugo M72 pieces?
sorry I thought you were talking m70 trunion.

the The RSB will be all custom and stay with the gun when the baarrels are removed the GB will be custom or L1A1 adjustable blocks on the barrels that are thinner no front sights or hand gurd bracket will be used cant have the RSB on the barrel if you want to unscrew it and most of the barrels except the super light one he will hunt with will be much bigger than a a m70 RSB any way. Im planing a couple versions some may be mostly stock appearing and Ill like do at least one open sight barrel as well for hunting in rain.
 
#48 ·
If you want to think "outside the box",why not start thinking of ways to make it work without the factory RSB and handguards. As you said, you could'nt screw or unscrew a barrel with the orig. RSB anyway.
Come up with a custom handguard arrangement that will work around your design, rather than hinder it.
Look at the way a Galil gas tube mounts and is held in place on an AK type receiver. Very easy to convert to a standard AK trunnion. It does away with the RSB completely but you still have a gas piston gun.
Just a few thoughts..........................
 
#49 ·
If you want to think "outside the box",why not start thinking of ways to make it work without the factory RSB

Thats a given and discussed some were on this site. The scope will stay on the gun when barrels are changed and I hope to be able to chart what barrels need what turns of the dials from a base setting so sight in not required for each barrel change.




there will be a custom RSB that holds the optics over the reciver. the hand guards will be floating with possably a bipod that folds into it flush fitting, the the GB's will be adjustable and will also use multipul ports on some of them , the entire FGC /trigger guardwill drop out of the reciver and there will be a target FGC and A hunting FGC that quick change, the Stock is undecided right now but likely a tumbhole set up in nice wood witha ajjustable comb and but pad, Im looking at stainless for the reciver, pushbuttion safety. muzzel brake that turns on and of as well as just closes the bottom in the prone position to keep dust down on some of the barrels, replacable ejectors, sleaved fitted bolts, ajustable rails that controll carrier play, a mag well that will accept more than one mag style.

It will be able to handle at least the following caliburs. 17-223, 17 remington, 223, 22-250, 22AR, 22 cheatah, 243 Win, 6.5 grendel, 260 Rem, 6.8SPC, 7mm-08, 7.62x25, 7.62x39, 308, 300 savage, 35,remington, 358win, 444marlin Rimless, 450 bushmaster, 410 SG and also looking at eventulay doing a blow back carriers for 22lr 22 mag 17hmr, 9mm, 45acp ect. also have some other ideas for a Saiga build that include 300 WSM and some wildcats based on it. Ive considerd SBR'ing it and even doing a couple shorty barrels as well. and I hope to be able to swap barrels from one build to the other so that is going to require a indexable GB likely.

about the only thing factory will be the carrriers bolts and trunion and they will be modifed. hell I even have a idea for a retractable sling. Im looking at engine turnig parts, engraving, electricaless nickel finish on the steel parts, titainum, carbonfiber, ect.

The 223 heavy varmit barrel arrived today. as well as some 300 Savage brass.

I could have just got him a browning BAR in 243 for much less but what fun would that be. This build/buids will be a huge undertaking and its getting expensive. I hope to do my boy a basic 3 barrel set by spring to get him shooting and keep adding to it as time allows. Im considering getting a second 308 Saiga as a doner gun so I dont have to load light and all factroy ammo could be used. A lot is undecided and compormises will have to be made in some areas.

Here are some of the barrels for it so far I have others as well. Im starting to think I shold have just done a quick change remington 700 LOL
 

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#50 ·
I got to working on this some more today.

I found out that a 1 1/16"- 16 threads on the remington 700 barrels will not clean up at 1" OD. However after doing some measuring it looks like after facing the breach off so that the chamber is flush with the breach and not recessed that there is only about a half of inch of threads remaning. the barrel on a AK protudes past the bore about that and the OD would need to be reduced to under 23mm any way so this may still be doable with a remington factory chamberd barrel still with a 1"-12 standerd fine thread.

I have no idea if a 1-12 thread is sutiable to hold the barrel in but I suspect it is.

I chambed the Stainless barrel in 300 savage and so far so good I need to get the trunion bored about .020" bigger and threaded. and then try to thread the barrel on the lathe.
 
#51 ·
any of you engineer types know if a 1"-12 thread is sufficient to properly keep a rifle barrel in place?? Winchester uses 1"-16 threads. in not sure what formulas or calculations to use or how to do them if i had them. I think it would be fine. I also want to be able to account for the voids on some trunions that wont have threads.

looking for advice from guys who do this stuff for a living.

figure 65,000 psi chamber pressure and a .540 case head that will cover any likely magnum round down the road and giver a comfort zone on a normal round.

I see coarser threads on different rifles like the small ring Mauser etc, as well as smaller IDs on lever actions and other high power rifles. Id just like to get some thoughts on this before I sacrifice a trunion.

what is the name of the site that has all the home built guns and machine shop stuff???? Im drawing a blank. I know some of those guys deal in this stuff regularly.
 
#88 ·
any of you engineer types know if a 1"-12 thread is sufficient to properly keep a rifle barrel in place?? Winchester uses 1"-16 threads. in not sure what formulas or calculations to use or how to do them if i had them. I think it would be fine. I also want to be able to account for the voids on some trunions that wont have threads.

looking for advice from guys who do this stuff for a living.

figure 65,000 psi chamber pressure and a .540 case head that will cover any likely magnum round down the road and giver a comfort zone on a normal round.

I see coarser threads on different rifles like the small ring Mauser etc, as well as smaller IDs on lever actions and other high power rifles. Id just like to get some thoughts on this before I sacrifice a trunion.

what is the name of the site that has all the home built guns and machine shop stuff???? Im drawing a blank. I know some of those guys deal in this stuff regularly.
Are you thinking of the Roderus homegunsmith site?
 
#52 ·
Most large ring Mauser 98's are 1.1"-12 typically in a 1.400" receiver ring. This would give you a n average of .150 solid wall thickness, not including the depth of the threads. Small ring Mausers are .980"-12 in a smaller 1.300" receiver. They should have about a .160 wall plus the threads. We won't go into the large thread/small receiver or small thread/large ring variants here as they're a relative minority compared to the standard large and small ring configurations.

That said, .980"-12 should be fine for moderate sized cartridges like 250 Savage, 6.5x55mm Swede, 7x57mm Mauser and 35 Rem. This is per the "Mauser M98 & M96 How to build your favorite custom rifle" book by R.A. Walsh.

For the heavier loads you're talking about, you'll have to defer to someone more knowledgable than I.
 
#53 ·
I spent the day making a centering tool and plug gage with go/nogo guages to allow me to more easly set up a trunion in the mill and bore it.

I ran the boreing bar through an it cut really easy. i havent decided on the treads yet so I only made one cut of a few thousands.

Does any one know the thread size and pitch on a factory AK barrel????? Id like to know the pitch mainly.

Im still torn between 1"-12 standard and 1-16 special like a winchester model 70
 
#56 ·
Im thinking a barrel nut with a sleave added to it that would shroud the barrel clear to the GB and just clear the gas tube would give a nice place to put a hand guard/fore grip or could possably be the fore grip. it would also allow the barrel to float.

Im about ready to start building this. thinking of a standard style normal looking recive first to work out all the mag issues and be a proof testing gun as well then build a very custom sporter from what ive learned . the 300 savaage barrel is chambered and profiled and the dies are here to reload as well as a factory crimp die just need brass. the 260 dies are coming and that barrel is in the lathe. Ill di pictures when I can do a pictorial
 
#62 ·
the 300 savaage barrel is chambered and profiled and the dies are here to reload as well as a factory crimp die just need brass.
Why do a .300 savage? You could do a .308 and load light for it at first, then when your son gets a bit bigger he can use the higher power ammo if he wants. Or does the savage round have the same rim size as one of the other rounds you're doing, as that'd make sense then you don't gotta make another bolt.

On placement of the gas block I'd put it in the AMD spot, it's a good compromise for keeping the weight to the rear, and having distance from the chamber to the gas port. I'd shorten the barrel a bit too, you could make it a lot lighter without losing too much performance, just go to around 18", but that's just a personal preference.
 
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