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Thread: barrell threading/headspacing.
10-05-2010, 02:17 PM #1
I am about to get a little project going, a bolt rifle in 7.62x39, and I need some advice. I am about to get an old bubba'd carcano and an sks barrel (un-ported for gas tube). I have never installed a barrel in a rifle before, and I was wondering about the threads so that I can plan ahead. I'm pretty sure the barrel will already be chambered, which Is why I am getting it (and it is cheap so good for first project). I am planning on just making a copy of the threads from the existing barrel on the new one, but was wondering about headspacing. how do you adjust it on these rifles? is it better to thread the barrel in a little deeper if it needs smaller headspace, or would you do something to the bolt itself? how tight of a fit do you want to make the threads and how do you know if it is screwed in tight enough?
before anyone gets to posting a bunch of "don't try this you will get killed" type of stuff, trust me, I am going to proceed with extreme caution. I have never done this but I have enough confidence in my skills that I think I can pull this off. and I am smart enough to operate this with a rope from far away one or two times too before I really trust it in front of my face.
any advice on installing a new barrel or links/books/etc that I should read are most welcome.
10-05-2010, 03:38 PM #2
The Carcano barrel threads are apprx. 14V TPI with an OD of 1.065" (this is from Frank de Haas' book, Bolt Action Rifles). I have some old books that probably cover installing a barrel, I think the authors are Howe and another by McFarland and I'll bet Midway has some videos of it on youtube. If I were going to do this, I would be inclined to get a set of headspace gauges and with them and the bolt and receiver, figure out where the barrel shoulder has to be. Measure from the front edge of the receiver back to the bolt face when in battery and then measure how much the gauges extend from the barrel and do the math. There will be some crush when you screw the barrel in that you will need to consider and probably best to err on the nogo side since you could always take the barrel off and remove whatever you needed to off the shoulder to tighten it up. Anyway, I used this method to rebarrel a Mauser 95 once it it worked okay. Or buy/rent a chamber reamer and tweek it in as needed.
How will you feed the rifle? Standard Carcano clips, a SKS mag or will it be modified to use AK mags?
10-05-2010, 05:46 PM #3
plan on doing the standard carcano mag, with maybe a permanent spacer to keep the shorter cased bullets from rattling around. I was also interested in this because it will give me the option of sticking longer bullets in the 7.62x39 case than are normally in there. once I learn some stuff about handloading and feel safe with basic rounds, I want to work up some heavy bullet subsonics for this.
was also thinking about what I could do with this action and .35 remington, since the cartridge base is maybe .010" over at the most from the carcano cartridge. but that will be a later project. worst case, I can always but the carcano barrel back on...
so about headspace gages, who to buy from? are there differences in what the actual russian chambering is and what we in america have decided it should be? I thought about making my own, but didn't want the hassle.
10-05-2010, 05:49 PM #4
also as to feeding, I had considered putting some sort of detachable magazine, but I already have a number of guns that give me that capability, and I am more interested in practicing and learning some basic gunsmithing skills than making the perfect rifle right off the bat.
10-05-2010, 07:00 PM #5
I buy stuff from Brownells but I believe Midway also carries what you need. Both also have all kinds of stuff that you will want.
10-05-2010, 07:13 PM #6
Keep in Mind
The SKS barrels are almost always chrome plated from the chamber to the muzzle. This will complicate any reaming you have to do to adjust headspace. Very careful measurement as described above will make this a moot point. Should make a neat little rifle. Good Luck, and regards, Clark
10-05-2010, 08:45 PM #7
I was wondering If It would work to thread in the barrel and use some shims to adjust headspace? I think the original barrels have a bit of a flange on them? If the sks barrell is not big enough to thread properly, I was planning on threading on an adapter bushing or brazing on some sort of bushing, and I could put a shoulder on that that stops against the front of the reciever. I wanted to avoid doing any reaming if possible anyway, but thanks for the tip on the chrome.
10-05-2010, 11:54 PM #8
Carcano with SKS Barrel.
Everybody has mentioned the Carcano Barrel ( 1,065x14TPI approx---27mm x 1,8mm pitch) BUT Nobody has mentioned the SKS Barrel, WHAT are its Thread dimensions ??? (if you are using an SKS threaded barrel...late production ones are NON-Threaded Press Fit barrels....)
The Solution in Australia, for both headspacing and correct barrel shank diameter for Threading, is
(A) find a good SMLE ( Lee-Enfield) Barrel, either Standard Light or a (H) heavy Barrel.
(B) Cut off the Threaded section ( which is also 14 TPI BTW) and Turn down the rest of the shank sufficiently to replicate the Carcano Threaded shank. One could possibly do this Turning and Threading Before cutting off the Threaded old section. (including a Carcano-style barrel shoulder)
(C) The Finished barrel will have a Chamber almost the same OAL and Specs as a 7,62x39 Chamber.
(D) Screw into Carcano Action, and then check headspace.
The way to ensure good headspace is to cut off a little less than the entire old thread, giving an "Over-Long" Chamber, then face-skimming off the excess until a perfect fit & HS is achieved in breeching-up.
BTW NB*** Get or make proper Carcano Barrel Vice and Receiver Wrenches...Both items are Round, so a clamp-style Vice and Wrench with Brass Lining/Bushes is Preferred ( Older Carcano barrels are Faceted,half- octagon style, with a round Base, making Vice manufacture an interesting process).
The .303 Br. Chamber is almost identical to a 7,62x39 case in its neck-shoulder and most of the body section to 39mm Length ( .303 is 56mm OAL).
By cutting off about 12-14mm ( .500-.550 inch) from a .303 chamber, one gets very close to the 7,62 Chamber length, allowing for the shorter 7,62 neck, and the protrusion of the rimless case to allow for the extractor to grab the rim.
With this system, NO Reamer is required, at most a little use of a Polishing stick at the mouth of the chamber. It also overcomes the problem of the Threads on an SKS Barrel being different from a Carcano, an, as yet, undetermined feature. (I have unscrewed SKS Barrels for rebuilding "Movie Guns", but mostly I have had newer Pressed barrel SKS examples, and they are a completely different kettle of Worms.
Also, with a .303 barrel rework, one can get longer ( and also heavier) barrel length ( about 24 inches) and the .310 projectiles of the SKS ammo work beautifully & accurately as Plinkers in .303 Rifles ( when loaded into .303 cases).
Magazine work: If you use the Carcano 6 round clip, Usually no "mag well Block" is required, especially if using Longer projectiles; DO NOT "single round
load," as the Bolt is designed to Pick up the round from the Magazine and allow the rim to hook up under the extractor...trying to force the bolt over a n already chambered cartridge will result in a broken extractor, or a broken ( and stuck) case rim.
Magazines: More work has to be done, to widen the Trigger Guard Frame internally, to allow a single column Tikka type magazine ( or one hand-made from steel sheet) to fit, after all the spring elevating mechanism has been removed from the TG body. Modification will also have to be made to the magazine (clip) catch, to hold the mag in place.
Over all, a non-reversible process, if one wants a Box magazine setup;
One could take a spare trigger guard box, and convert it permanently for a single column mag, keeping the original TG and Barrel if one wants to go back to 6,5mm....
Most reworked Carcanos used here at Gun Clubs as "
Hire and Try" guns, in 7,62, use the .303 barrel method.
10-06-2010, 11:09 AM #9
I figured that the method you describe is about what I will be doing. the SKS barrel has no threads (is a press in type) But I have lathes that can cut threads, so this is not a problem. as to the magazine, I was going to use the original for now, but will probably end up changing this out for a small 5 or ten round magazine of some sort. I am pretty handy with welding and metal fab and should be able to make something work, or make one from scratch if I get determined enough.
p.s. thanks for the tip on sticking single rounds in there. I read about that last night somewhere else, but had forgotten already.
10-06-2010, 03:20 PM #10
how tight do I want to screw in the barrel? is there a specific torque range that is acceptable or just keep on turning until it is in there really tight and hard to get back off?
10-07-2010, 06:21 AM #11
10-13-2010, 01:07 AM #12
so I got the SKS barrel in the mail today. still waiting on my carcano's to ship. (I got a couple while I was at it since they were going so cheap). The sks barrel is a little under 3/4" in diameter at the chamber end. chrome lined bore. as someone noted previously, the receiver has threads a little over an inch.
my options to make this work were to braze a bushing on to the barrel to make it large enough to fit in the carcano receiver and thread that, or to thread the bushing onto the barrel and then thread the bushing on the outside so that it fits the receiver. one last option I just thought of would be to press fit a bushing onto the barrel and pin it in place and then thread the bushing to fit the receiver. what of these is the best option? Am I going to ruin the chrome plated chamber by heating it up while brazing it?
I recently found a slightly bubbaed enfield no. 4 Mk I* from 1943 that I picked up for cheap. I don't want to use it, for this, though, since despite the butchered stock, the mechanical parts are in nice enough shape that I think I am going to leave it in .303 brit unless the thing shoots like total crap.
10-13-2010, 11:12 AM #13
There is no need to braze a bushing to the barrel. Make the internal thread a snug fit and use red Loctite(271) to stick it to the barrel thread. The external thread to fit the receiver should be loose enough to hand turn easily and come to an abrupt stop when the barrel shoulder hits the squared, burr-free receiver ring. Check for complete contact with marking compound or fiber tip marker ink on the face of the receiver ring and the barrel shoulder face.
Turn it up tight with your receiver wrench several times to to burnish the threads( lightly oiled) and mating surfaces to get rid of burrs and minor machining marks. Final installation torque should be about 100 ft-lbs.
Then you can calculate chamber depth by measuring the depth from the receiver ring face to the bolt face. Cut the chamber and install the barrel. Test fire. Stamp the cartridge designation on the barrel. Done.
10-15-2010, 02:43 AM #14
Where did you find the cheap Carcanos ???
10-15-2010, 08:48 AM #15
they are out there if you look. I wasn't going for the most prisitne perfect collectors, which I have seen in the $350-$500. the slightly bubba'd ones tend to go for closer to $50-$100. you just have to study what is out there and what you are looking at.
05-14-2012, 11:04 PM #16
Just wanted to say thanks to all who gave me advice on this. I finally made the time to follow through on thous and took my first test shots this evening. The first from about 30' away behind a tree, then after inspecting the fired case and the gun for signs of trouble, the second with the rifle shouldered. Now all I need is some sights, and maybe muck about with the magazine. I have some options on both I will explore soon.
Anyway, long story short, if you teach a man to fish, he will never go hungry; if you teach him to run machine tools he will probably build some guns.