Barrel Re-Thread

I'm leaning towards trying a rethread of 20TPI over the 28TPI threads first. If it works out and I can get the final product to line up properly then it'll be great.

If that fails I will turn down the threads and weld on a 20TPI sleeve which will allow me to ensure the sights are vertical.

If both of those fail somehow I will go with a new blank.

Wish me luck.
 
Does the old barrel have sights that have to clock straight up?

I so, you may have to take a little off the breech, the shoulder and ream out the chamber a little.
 
Just an opinion:

As cheap and easy as it is to get a chunk of 9 mm bbl blank,you have lathes available...and you are pondering cutting threads over threads,or welding and?????

The shortest distance between two points is a straight line.You have a ruined barrel,scrap it,put a new barrel in and do it right,the first time.

IMO,if you are dealing with gunsmithing ,barreling and chambering,there is a standard to work to.You do it right!You do not know who may put their face behind your work.You take part of the face or sight from someone trying that piece and you own it.You did it.

If you want to play around and do something creative,make sights,glue wood on,add a recoil pad.That won't hurt anyone.
 
If you just cut 20 tpi threads over the 28 tpi section, you will have very weak threads about. 013" deep. I agree with HiBC, just do it right.
 
I had a little free time today and got around to fixing the barrel. I went with the threaded sleeve which allowed me to clock the threads and align the sights with vertical. It tightened down to 200 ft-lbs and looks like it came strait from the factory...win in my book.

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Since it was a loose sleeve I was able to clock the threads and align the sights with vertical. It tightened down to 200 ft-lbs and looks like it came strait from the factory...win in my book.
 
The chamber remained untouched and is still 100% factory. It looks like it got some weld on it but it didn't. I just cleaned it up on the lathe afterward and it was hard to tell it apart from the original barrel.
 
Ok,well,it looks like you did a nice job of executing your plan.Good job!

Now,no disrespect intended,I do not mean to rain on your parade.I'm going to give you something to think about.It has to do with safety.I would not take the time to write this over whizzing contest,but it is always OK to speak up over safety.This is about not getting someone hurt.Probably the arteries,nerves and tendons of the left hand.

Barrels are not static,they have harmonics,whip around some,do a tuning fork thing.Take your 12 in scale,hang it over the bench,whack the end of it,watch it vibrate.It curves,whips,spreads out the forces.Put a little notch in your scale,or use a glass cutter on glass,etc,you make a stress riser.A weak spot where all the flex occurs.It fails.

You reduced the wall section around the chamber by about half,yes?So now,the chamber is a smaller diameter,thinner walled tube than designed.The sleeve re-enforces it?Not really.Look at your pix,at the dead sharp corner at the shoulder.That is your stress riser.All the weight of the barrel and vibrations will focus on that corner,and your sleeve does not help it.Maybe it won't fail.I believe in Murphy's law.If it does,the barrel will blow forward,38,000 psi of hot gas and maybe some shards will cut into the inside of someones wrist.

So,my suggestion:You proved you have the skills to get her done!!You just took a wrong turn.

Go back to Wyosmiths muzzle pickle idea.Make the coolest muzzle brake in the world.Make it slip on the muzzle and give it that nice 360 degree full weld.You can get your legal length and the BATF will be happy.I suggest you freebore the muzzle under the weld so any distortion will not affect the bore.

Even 10 in of bore will give a 9mm good ballistics.Barrel length is only a legal requirement.Now,you can set up and cut off your practice job,and make that barrel shank and chamber again with virgin steel,to full original design,and it will never fail,and you will know you did it right.

Just my opinion.Please,understand I'm not in any way trying to put you or your work down!!Keep it up!!

If you have a nice little carbide boring bar,or a Bokum Cobalt,etc,and a chamber drawing,I bet you can bore a fine chamber without a reamer for a 9mm.
 
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I ran the numbers several ways...chamber pressure, and vibrations.

Pressure-wise; both the hoop stress on the reduced chamber diameter, and the axial stress on the welds are well below what the material will hold (even with the weakest of steels and a fairly high design factor).

Vibration-wise; as a dynamic/shock loaded cantilever made from a non-brittle material with a stress concentration at the chamber/thread shoulder it is also well within any forces it will see. It would take someone jumping on the end of the barrel with the action in a vice to do any damage. Surprisingly, both the shear and bending moment diagrams are fairly linear without even taking into account the barrel shoulder that's contacting the action.

I understand the concern and will certainly keep a close eye on the barrel, but it should be amply strong to handle all forces it will see.
 
OK,well,reminds me of some young engineers I have worked with...

I just use my eyeball.You may well be right,and,as I said,no whizzing contest intended.

My compliments.
 
Good topic

I had been wondering if a threaded sleeve would work. I am building up do do stuff like this (got a lathe this summer but not there yet). It seemed to me that a helicoil type idea would work. I was thinking leave the barrel as thick as possible, but turn off the old threads, and turn in new ones. Then inside thread the sleeve to match the barrel leaving it longer than the shank, then with sleeve threaded on tight and locktighted, turn and thread the outside. So long as the sleeve is thicker than the threads, it would seem the threads would be the weak link. Enjoyed the discussion.
 
It works if you watch not to thin out the chamber wall too much. I would not advise welding a barrel, but in this case I think he will be fine because of the low pressure round. It amazes me how people are scared @#$%less of heating up a bolt to weld a handle on but will break out the welder the minute they have a barrel problem. Welding on a high power barrel will either anneal the barrel or harden it more, but it will not "Do nothing".
 
That's what's nice about TIG. You can use a low amperage (20A in this case) to get the job done locally without heating up the rest of the barrel. I did it in stitches while the threads and chamber remained cool/warm to the touch. Of course it's impossible to exactly match the cooling conditions of the original steel so it will be slightly different...but not remotely enough to worry about...especially in a 9x19mm chambering. I agree with the previous poster that one might start getting concerned about things with a high pressure round, and especially if more invasive work was required. Once again, running the numbers, even the reduced chamber diameter (pre-sleeve) was plenty thick to handle a hot 9mm and then some. This barrel should hopefully last through anything short of the previous owner's screwup.

I can't wait for the heavier spring and buffer to show up this weekend so I can try it out :)
 
What the heck is "Soft steel"? A Mauser receiver and Russian receiver are "soft steel". Somewhere in the 1018 to 1030 range. A high power barrel is usually 4140 or 416 series steel.
 
Gun barrel steel is heat-treated through to about 28 on RC scale with no carbon added. .22 and old low pressure round barrels were made of lower grade steels with no heat-treating and some may still be. Point is, you have to introduce carbon to "Soft steels" to harden them. High power barrel steel could heat-treat itself just from welding on it. Welding usually anneals gun barrels, but it could go the other way. Under the right conditions, barrel steel can be made so hard that a carbide endmill will barely put a dent in it.
 
Gun barrels steel is a alloy
A tool steel as you said 4140 or 416 stainless
It is not heat treated to hardness but normalized it is already has the charrestics needed to be a gun barrel, but if it was hard it could not be machined or drilled with a gun drill or a rifling button pushed or hammer forged.
The steel is malleable
http://www.thefreedictionary.com/_/dict.aspx?word=malleable

Here is a article from a random google search
http://www.lasc.us/RangingShotBarrelMakingFeature.htm

And wiki about Rockwell hardness
http://en.m.wikipedia.org/wiki/Rockwell_scale

It is true that barrels can be hardend, they are made of a tooling steel
But TiG welding can be used to a controlled method by a good welder.
 
I am not going to waste my time looking up stuff on the internet. You do not know what you are talking about. I have run miles (Literally) of 4100 series steel on lathes and mills and heat treated quite a bit of it. "Normalized" 4140 is heat treated 4140. It is commonly referred to as "Pre-heat" or "Brake" steel. I have drilled and tapped a lot of Arisaka receivers and they are at 35-38 RC. I have seen adds for gun barrels that say "Re-Sulphurized!" This will give you the indication that it is soft steel because it cuts shiney and greasy like Ledloy. Sulfur is added to make machining easier and adds to tool life. The barrel is still around 28 RC, but now it has dirt (Sulphur) in it.
 
Ok good for you
I have 30 years as a moldmaker and gunsmith
And that I guess is less than miles of experence.

And I have been welding for several of those years.
And surprize so has a lot of gun manufacture weld and even -gasph-silver solder
Parts on gun barrels
H&R has done that for decades. Those barrels sure don't blew up.

But I don't know nothing. Fine good excuse for contotinuing learning.
 
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