threading a press fit SKS barrel
I am working on converting a carcano to 7.62x39 (finally getting started!), and was wondering about threading my barrel. I bought a while back, a chinese sks barrel that is intended to be pinned into the reciever. I was wanting to thread this and the inside of the existing barrel stub so that it is easier to headspace. I am leaning towards the lock nut system used on the savage rifles. How thin can the chamber area be before it is too thin? this barrel is .750" at the breach, but cutting threads into this is going to weaken that area a bit. the other option is to bore out the existing barrel stub and press fit that into the action, holding it with loctite (or brazing it), and pinning it for good measure. after threading I will only have a wall thickness of .113" if I thread to a standard 3/4-16 pitch. is that enough?
Why use a standard COARSE thread????
You can gain a lot of room by going to a very fine thread. Commonly used on revolver barrels... Dan Wessons were around 40 TPI. The minor diameter of Carcrapo barrel threads is ~.968. Plenty of room for just threading the exisiting OD of AK barrel when you use a very fine thread..
You have to bore stub anyway, a small thread cutting tool in boring bar will make quick work of it.. Thread barrel stub first, use as a gage to thread barrel.. You need fit to be close with fine threads.
If it was a more powerful cartridge, I would not do it that way... (would get a proper barrel blank)
Using locktite is a terrible way of mounting a pressfit barrel. Press fit alone, is a poor idea. ( even most .22 rimfire rifles have a cross pin.... ) What if somone reblues it??? Locktite does NOT like heat.
I would thread directly into the reciever if I had a barrel big enough to do that, but this one is only .750 at the breach. I would never want to loctite something in place without a cross pin too. press fit is nice enough if you have a long enough press to fit a barreled action in it. sometimes you've gotta work with what you've got. or spend a bunch of money on different parts or tools. I will look into other threads that I can use since I have a barrel stub to work with to thread the new barrel into, and thread that whole thing into the action.
Threading to 3/4 - 16 UNF the chinese 19mm SKS barrel and 3/4-16 UNF tapped old Carcano barrel stub in a lathe worked for me. Head space is then achieved screwing the new barrel into the stub. I used a drop of silver solder (braze) to lock that position firmly. It has held nicely for the past 25 years.
You may also want to consider a SMLE barrel for your conversion. It is the correct bore diameter and the front end of the .303 British cartridge is essentially the same as the 7.62X39 so you just have to trim a bit from the breech end of the barrel. It will not have a gas port to plug either.
I considered this, but the barrel that I found was new and chrome lined, and most importantly for my first attempt at something like this- cheap. I wish I had bought a few more from sarco when I got this one... alas, I did not. Because it is new, there are no holes to plug. It also had some other benefits, like having the twist rate I wanted, and the chrome lining that would make it less prone to damage from the slcheapie surplus ammo out there still to be had.
Originally Posted by Gazz
You got the SKS barrel cheap - so keep it simple - like you said yourself. Bore out the barrel-stub to an interference-fit on the SKS breech. Put the SKS into a bucket of ice [or use CO2 to cool it] and heat the Carcano-Stub to 500°C or more and push it onto the SKS Barrel. If the expansion of the Carcano-Stub is adequate, the force required to locate it onto the SKS will not require a purpose-built hydraulic-press but the subsequent shrinkage will return the 'relationship' to interference and so a pin or a little brazing will secure it permanently. The head-spacing then can be done by trimming the shoulder on the Carcano-Stub. Good Luck!!
thanks for the advice, in this case I decided that it would be easier to just go ahead and thread the thing in and use a lock nut. was much easier than I imagined, and seems to have worked pretty well. Just need to add sights or a scope and go out and have fun.
Originally Posted by Browndoff