Repair damaged barrel threads

[Ggmac]

He said it was a small shank . Most mate blued savage rifles have a decent amount of steel shot in the receiver , nut section , if this isn't blown out or washed out it will gall the threads . Most savage factory barrels I've removed lately have a flat crest .

 

[savagedasher]

He said it was a small shank . Most mate blued savage rifles have a decent amount of steel shot in the receiver , nut section , if this isn't blown out or washed out it will gall the threads . Most savage factory barrels I've removed lately have a flat crest .

If was a stainless barrel he would of never got it off. Larry

 

[ireload2]

If the threads were cut to the right pitch diameter the tops of the threads should be flat with the major diameter under size by .017.

If you drag out Machinery's Handbook you will find a reference section on threads that says there is only 3% difference in the strength of a 100% thread and a 75% thread. The little areas at the thread peak (major diameter) add very little strength.

It sounds like Savage made the barrel undersize on the OD. Most barrels are undersize a few thousandths on the thread major diameter because it has little value to make the major diameter right on the money. Vee threads are used for economy - they are easy to produce. The tooling (tool bits and dies) are easy to make. The threads are easy to cut and easy to gauge.

 

[shortgrass]

When I thread a barrel tenon, I start with the major diameter called for. If its an inch, I make the tenon blank 1". When I am finished threading I lay my 10" mill bastard on the thread and make a few revs. Measuring after, I'm .005-006 smaller on the major. I completely understand what is wriiten in the"handbook", but .017" is 'hardware nut and bolt', imported from Bangladesh stuff. By the way, I'm not looking for that aircraft fit. I want a bit of 'wobble'. Threads are "fasteners", not alinement devices. That's what the square shoulder on the barrel and the receiver are for,,,, alinement. But, what can or should you expect from production rifles? Probably lots of wobble from sloppy machining thats made so everything will at least screw together, no matter what bin it comes out of.

 

[Archis]

I'm on the road for the next couple of days, but I will report back with pictures of the barrel. The scope base screws were removed prior to barrel removal. Threads from the start of the shank on the barrel to the breech face are all damaged. Once I had the action off, I stripped it down and dropped it in the sonic cleaner. Once cleaned of whatever was built up in it, the new barrel went on smooth as butter.

I measured the outside diameter of the damaged threads with a mic and the flattened threads measured 1.038" major diameter. Wouldn't have been able to use a thread mic, too much galling. The Shilen barrel I installed had a major thread diameter of 1.047".

 

[billlarson]

So I'm a little embarrassed to post this as this was my own dumb mistake. I was attempting to remove the barrel on my Savage 12FV and I pretty thoroughly borked the threads on the factory barrel (.308 Win). I think I spun the barrel nut too far forward on the barrel and flattened a portion of the threads. On removing the nut, I noticed that the barrel threads were squared off. Let me add that this barrel was practically glued to the action. Once the barrel nut was loose it still took repeated blows with the hammer on the action vise to spin the action off. Nothing spun freely off the barrel so I didn't notice the damage till it was too late. The action is not damaged and is already wearing a nice shiny new 6.5x47 Lapua (with a new barrel nut of course).

I'd like to be able salvage the old barrel, if possible. It was an OK shooter. The OD on the damaged barrel threads is 1.038", and I know a factory barrel should be at 1.055". Assuming I run a 1-1/16-20 die down the damaged threads, I'm more than likely still stuck with threads that are .017" too small in OD. Am I playing with fire here? Is this a bad idea and I should just chuck it into the garden? In shame, I ask for your advice.

P.S.A. Don't do gun smithing in your garage at 11:30 at night. You do dumb things.

I HAVE STRAIGHTENED OUT BOTH RECIEVERS AND BARREL THREADS THAT GOT GALLED,DINGED... LATHE SET-UP.... CREATES NEAR NEW LOOKING THREADS........
BILL

 

[Cold Bore]

The scope base screws were removed prior to barrel removal.

No they weren't.

Savagedasher told you, four separate times, that they weren't, so it must be true.

Just cause you were actually there doesn't trump what somebody guesses on the internet.

 

[hogpatrol]

 

[centershot]

The gunsmith that replaced the factory barrel with a prefit Shilen said that Saveage must have bead blasted the barreled action. The threaded area was full of what looked like glass beads. Made the removal a challenge.

 

[Ggmac]

See post #21 . I wonder what savage spends on steel shot . I must have a pound from cleaning it from the joints .

 

[Archis]

Okay, here are some photos of the damaged barrel, alongside the the Shilen I replaced it with. I remeasured for sanity sake and this is what I am seeing:

Factory .308 Small Shank (damaged): 1.042"
Shilen 6.5x47 Small Shank: 1.051"

I'm dropping the barrel off with a smith tomorrow to see what he can do with it. If he can clean up the threads with minimal effort, great! Otherwise, it's off to the boneyard (or some other project).

 

[Titan700]

Yelp thank savage for all the shot , you can see it in the barrel threads.

 

[savagedasher]

No they weren't.

Savagedasher told you, four separate times, that they weren't, so it must be true.

Just cause you were actually there doesn't trump what somebody guesses on the

Okay, here are some photos of the damaged barrel, alongside the the Shilen I replaced it with. I remeasured for sanity sake and this is what I am seeing:

Factory .308 Small Shank (damaged): 1.042"
Shilen 6.5x47 Small Shank: 1.051"

I'm dropping the barrel off with a smith tomorrow to see what he can do with it. If he can clean up the threads with minimal effort, great! Otherwise, it's off to the boneyard (or some other

Yelp thank savage for all the shot , you can see it in the barrel threads.

Glad I seen the pictures . I don't see any reason to say more. But it's good thing it wasn't stainless . Larry

 

[Archis]

I contacted the guys at 4D Reamer Rentals and they were nice enough to rent me a 1.055x20 thread die. I say "nice enough" because apparently people have tendency to treat the rental tools tough enough that they no longer advertise renting that tool out. I was able to run the die down the threads and clean them up just enough to get rid of the galling. OD of the threads is still at 1.042" (what else would it be I guess). I test fit the barrel to the action and the fit was surprisingly tight, just as tight as the Shilen barrel which has on OD of 1.052"

Out of curiosity, I wanted to see what kind of safety factor we were looking at between a 1.052" thread and a 1.042" thread. I have access to Inventor and have used it sparingly for simulations at work. I will add the caveat that I'm not a mechanical engineer, so take these results with a grain of salt. I modeled a section of the threads of the action (per the thread spec) as well as those of a barrel with a thread OD of 1.052", 1.042" and 1.03" (just as a hypothetical). I then added an 11,000lbs force (to simulate typical .308 bolt trust) along the axis of the barrel threads. I figured that if threads were going to fail, they would fail in shear along the axis of the barrel. The tested material was 4140 steel.

The results were a little surprising. Basically, anything below a safety factor of 1 means that the steel is stressed to the point that it is permanently deformed (i.e. They start to shear off). A barrel thread OD of 1.052" (Shilen barrel, un-damaged) had a safety factor of 1.63. A barrel thread OD of 1.042" (Savage barrel, repaired) had a safety factor of 1.58. I had to cut the barrel threads back to 1.030" to get below a safety factor of 1.

I'm going to have the gunsmith I talked to last week inspect the repaired threads and fit with the action but I'm feeling that the barrel may be salvageable. Just thought I'd share where I'm at with this project.