First time rebarreling questions

[dgeesaman]

By a machinist and benchrest gunsmith.

That’s half of my problem. I’m a Mechanical Engineer, which means I can ultimately understand the ideas and most machining issues, but my conversations with gunsmiths have to crack thru the preferred lingo and in some cases either of us make assumptions. The gunsmiths know this stuff as second nature and I use the wrong words and meanings.

Since we did get specific, If I were asked to make a drawing of a barrel, I’d spec a Class 1 thread. Anything sloppier than that will have uneven distribution of the preload, lower strength, and generally higher risk of b***hing up. Makes no sense to contain a combustion event with loose threads.

 

[alinwa]

That’s half of my problem. I’m a Mechanical Engineer, which means I can ultimately understand the ideas and most machining issues, but my conversations with gunsmiths have to crack thru the preferred lingo and in some cases either of us make assumptions. The gunsmiths know this stuff as second nature and I use the wrong words and meanings.

Since we did get specific, If I were asked to make a drawing of a barrel, I’d spec a Class 1 thread. Anything sloppier than that will have uneven distribution of the preload, lower strength, and generally higher risk of b***hing up. Makes no sense to contain a combustion event with loose threads.

And I use mechanical engineers every day on my job and stuff like this is frustrating

You'se guys have a severious difficulty separating the wheat from the chaff..... LOVE ya's (two of my sons are ME's) but I could tell stories for DAYS about arguing with engineers...

firstly, assumptions;

".....Anything sloppier than that will have uneven distribution of the preload, lower strength, and generally higher risk of b***hing up...."
"....Makes no sense to contain a combustion event with loose threads....."

These statements makes no sense.....

Not only are they irrelevant and misinformed, they make assumptions with no reasoning..... what is "makes no sense?"

First of all, you're not "containing a combustion event" and secondly your statements concerning tighter fitting (less clearance) are simply flawed..... and "strength" has absolutely NOTHING to do with it, NOTHING..... until we start stripping threads or wringing tenons off, let's let the "strength" issue lie shall we?

And thirdly, looser thread fit offers distinct benefits, several of which aren't mentioned here,

and lastly for now..... thread loading is a funny thing. Ideally IMO a barrel-to-action threaded tenon connection should only have about 5-7 threads in toto.... because that's all you can truly engage in the setup with the first couple wraps doing 50% of the work by theyselves....... and the last half of the typical tenon just hangs there in space, flopping about irrationally. But rednecks buys the guns and pays the bills and "ever'body KNOWS that long tenons are "better"" even though no one can define WHY!

A long time ago I went to a builder friend for advice on building my first home..... I asked "how do I pick my subcontractors?" And his reply is not only relevant today, and to this subject, but could be the single best piece of advice I've ever gotten re having stuff built. He said "YOU DON'T!!" His statements were quite explicit.....

"You simply don't know what you don't know." and

"You're incapable of picking good people because you don't know what's important" and

"You don't even know which questions to ask..."

All re-stating the thing that's now obvious to me. I DIDN'T EVEN KNOW WHAT WAS IMPORTANT!

So now I buy construction contractors (and gunsmith's, and engineers of all sorts) based on reputation, presentation and performance record. And not "he's a nice guy" reputation but reputation of winning. And slowly over many years of spending many thousands chasing my idea'rs around I'm sorting out some of the relevancies.... just last night I had a true quandary. I fitted a barrel to a Kelbly Kodiak KNOWING that in the not too distant future another gunsmith of my distant acquaintance was going to take it off. Consequently I fitted it tighter than is my wont. STUPID and small-minded of me but in this case I had to weigh several extra extenuating factors into the mix. And I chose to "err on the side of caution" which in this case means "err on the side of redneck"...... knowing full well that in the end reputations are most often based on salesmanship, not performance.

 

[hogpatrol]

Reminds me of that meme where a white hat is telling a construction guy "I don't know how to do your job but my book says your doing it wrong". I found it, it was a yellow hat.
The best MEs are the ones who first went through a four year machinist apprenticeship.
The worst are the ones who mistakenly think a piece of paper makes them think they're smarter than a guy in the trenches who. on their own, is tasked with fixing their miscalculations. BTDT

 

[dgeesaman]

View attachment 1067169 Reminds me of that meme where a white hat is telling a construction guy "I don't know how to do your job but my book says your doing it wrong". I found it, it was a yellow hat.
The best MEs are the ones who first went through a four year machinist apprenticeship.
The worst are the ones who mistakenly think a piece of paper makes them think they're smarter than a guy in the trenches who. on their own, is tasked with fixing their miscalculations. BTDT

Alright alright I deserved that, class 3 threads have the closer tolerances, not class 1. (Which of course is not how metric threads are classed where a g tolerance thread is better than e). So for highly stressed threads the aim is perfectly consistent threads that will share load better. Serves me right for using a stupid phone for this and not looking at my Machinery’s Handbook.

Barrels are containing a combustion event. The bullet is not up to speed until it’s well into the barrel. There is pressure in the chamber until the bullet exits, and the empty bore behind the bullet sees what the chamber sees.

In all seriousness, I have no equipment or skill to learn gunsmithing and design but I’d like to learn more about it. If anyone has a book or reference where I can begin, I’m interested.

David

 

[hogpatrol]

Forget on which forum it appeared, but Alex Wheeler posted a photo of a barrel he removed with tenon threads that looked like they were chiseled and the rifle still shot well.
I bought a used Remington that had been rebarreled to a 6BR and probably fifteen to twenty percent of the threads were filled with some sort of goop. After cleaning, the od miked at 1.047. I didn't bother with the root diameter.

 

[alinwa]

Alright alright I deserved that, class 3 threads have the closer tolerances, not class 1. (Which of course is not how metric threads are classed where a g tolerance thread is better than e). So for highly stressed threads the aim is perfectly consistent threads that will share load better. Serves me right for using a stupid phone for this and not looking at my Machinery’s Handbook.

Barrels are containing a combustion event. The bullet is not up to speed until it’s well into the barrel. There is pressure in the chamber until the bullet exits, and the empty bore behind the bullet sees what the chamber sees.

In all seriousness, I have no equipment or skill to learn gunsmithing and design but I’d like to learn more about it. If anyone has a book or reference where I can begin, I’m interested.

David

Barrels are containing a combustion event. The bullet is not up to speed until it’s well into the barrel. There is pressure in the chamber until the bullet exits, and the empty bore behind the bullet sees what the chamber sees.

Yeahhh, well, duhhh... Just cuz I ain't got a degree don't mean I can't iterate the obvious with the best of them.....

So, riddle me this (note that you're posting with someone who's actually done this test... I ain't theorizin') in your estimation/guess/handbook-based SWAG make an assessment of the following;

A chambered 308 Win Palma barrel, in hand, NO ACTION nor other appurtenant parts, JUST a chambered barrel. But a real barrel off a competitive Palma Rifle and we'll add legal Palma 308 ammunition just for SAG....

So, holding the barrel in a vise, insert a round and fire it by striking the primer with a hammer and nail.

Barrel/loaded round/hammer and nail. NO action, NO interaction with the class I or II or III t'reads A'tall....

Does the bullet go out the barrel?
Does everything blow up?
Does the case go shooting acros't the room illustrating Newton's Third Law Of Motion?
Or something el'tse entire????

Now, books..... I've got 'em ALL. Yes, I too can read, over 3500 actual paper and ink BOOKS in my home. May I suggest you beg borrow or steal a copy of Harold Vaughn's 'Rifle Accuracy Facts'.

It'll reset yer clock

RAF may be hard to access......library I'm guessing, maybe. I've got 3 copies but they don't get loaned out except to folks who've earned the right to walk in on me unexpected. At 3AM, unannounced.....

Easily accessed are works by Colonel Townsend Whelen, P. O. Ackley, Julian S Hatcher, Elmer Keith, William Hambly-Clark to get you started...

 

[alinwa]

And speaking of threaded joints and things blowing up...... gotta' love the innertube....there's a ton of these but I hadn't seen this one 'til today

 

[alinwa]

And another image to pique your interest...... this sort of thing spawns endless discussion and idiotic "fixes" on Rollicking Around Ye Happye Kempfire Comparing ELR Shots And Tattoos forums acros't thee land.

How could THIS happen??

 

[dgeesaman]

Barrels are containing a combustion event. The bullet is not up to speed until it’s well into the barrel. There is pressure in the chamber until the bullet exits, and the empty bore behind the bullet sees what the chamber sees.

So, holding the barrel in a vise, insert a round and fire it by striking the primer with a hammer and nail.

Barrel/loaded round/hammer and nail. NO action, NO interaction with

Does the bullet go out the barrel?
Does everything blow up?
Does the case go shooting acros't the room illustrating Newton's Third Law Of Motion?
Or something el'tse entire????

Now, books..... I've got 'em ALL. Yes, I too can read, over 3500 actual paper and ink BOOKS in my home. May I suggest you beg borrow or steal a copy of Harold Vaughn's 'Rifle Accuracy Facts'.

It'll reset yer clock

I have definitely not done this. I also didn’t cheat and try to find an answer. I didn’t attempt any math stuff.

The bullet should not get far down the barrel, because if the powder lights, and I expect it will, the powder will burn at low pressure without a lugged bolt to keep it chambered. My guess is the pressure will push the case back off the bullet. Some blowby and maybe the primer will pop out and give you a Roman candle?

What really happens?

 

[hogpatrol]

http://forum.accurateshooter.com/threads/barrel-tenon.3920701/

Check out this Class X thread job then go to page two of that thread for more info.

 

[gunsandgunsmithing]

Alright alright I deserved that, class 3 threads have the closer tolerances, not class 1. (Which of course is not how metric threads are classed where a g tolerance thread is better than e). So for highly stressed threads the aim is perfectly consistent threads that will share load better. Serves me right for using a stupid phone for this and not looking at my Machinery’s Handbook.

Barrels are containing a combustion event. The bullet is not up to speed until it’s well into the barrel. There is pressure in the chamber until the bullet exits, and the empty bore behind the bullet sees what the chamber sees.

In all seriousness, I have no equipment or skill to learn gunsmithing and design but I’d like to learn more about it. If anyone has a book or reference where I can begin, I’m interested.

David

You're going about it all wrong, but it can work. As I said earlier, shooting forums aren't the best place to learn machining. Learn machining and then learn how to apply it to gunsmithing and visa versa. There are things inherent to gunsmithing that aren't common in machining but when any type of metal work is concerned, it's mostly the other way around. IOW, learn machining first. By and large, gunsmithing work is crude and simple as compared to much of what a good tool and die man will do daily. So, a good machinist with a good understanding of what matters and what doesn't in gun work, has the makings of an excellent riflesmith.

 

[Ggmac]

I have definitely not done this. I also didn’t cheat and try to find an answer. I didn’t attempt any math stuff.

The bullet should not get far down the barrel, because if the powder lights, and I expect it will, the powder will burn at low pressure without a lugged bolt to keep it chambered. My guess is the pressure will push the case back off the bullet. Some blowby and maybe the primer will pop out and give you a Roman candle?

What really happens?

I would say it depends on the case design , bore and powder . It could detonate ( black powder ) thus propelling the bullet and case ( if the case was wedge shaped and chamber smooth ) if the case had near parallel sides and a rough chamber it could seal enough to propel the bullet from the barrel ( length is factor )
Ackley did some experiments with a lever gun and removed the link , thus having no lock up just the lever and bolt , gun fired normally .

 

[alinwa]

I have definitely not done this. I also didn’t cheat and try to find an answer. I didn’t attempt any math stuff.

The bullet should not get far down the barrel, because if the powder lights, and I expect it will, the powder will burn at low pressure without a lugged bolt to keep it chambered. My guess is the pressure will push the case back off the bullet. Some blowby and maybe the primer will pop out and give you a Roman candle?

What really happens?

It fires.... with deadly intent.

Just like the shotgun in the vid above. That's not fake, you can make a shotgun out of water pipe, no lockup system at all.

And the next pic of the "popped up" primers? Those were simply rounds loaded with excess headspace, the primers popped out until they hit the boltface, they would have popped clear out but that's not the important takeaway..... what's important is, THE CASE DID NOT MOVE!!

"Barrel in the vise"..... if you take the experiment just far enough (which we did) so that you slide the hammer (actually a small iron bar) down a channel to impinge the primer the weight of the "hammer" is enough that the case seals normally, the "hammer" bar pops back a foot or two and sometimes the primer dribbles out but not with force.

And then you reach out and extract the case with your fingernails.......

 

[dgeesaman]

It fires.... with deadly intent.

Just like the shotgun in the vid above. That's not fake, you can make a shotgun out of water pipe, no lockup system at all.

And the next pic of the "popped up" primers? Those were simply rounds loaded with excess headspace, the primers popped out until they hit the boltface, they would have popped clear out but that's not the important takeaway..... what's important is, THE CASE DID NOT MOVE!!

"Barrel in the vise"..... if you take the experiment just far enough (which we did) so that you slide the hammer (actually a small iron bar) down a channel to impinge the primer the weight of the "hammer" is enough that the case seals normally, the "hammer" bar pops back a foot or two and sometimes the primer dribbles out but not with force.

And then you reach out and extract the case with your fingernails.......

Wicked. So the case grips the chamber and holds the pressure that thoroughly. Aside from the primer impulse then, very little load shows on the lugs.

That makes your point

David

 

[Will Henry]

That's not entirely true. The case will contain the pressure within a fairly narrow parameter. Pressure has to be sufficient to allow the case to grip the chamber wall but low enough that backthrust does not exceed the elastic limit of the brass. Now, it doesn't take much pressure for the head of the case to deflect, if only very slightly. Since a front locking action will deflect very little, the grip of the case on the chamber wall is of no consequence. If pressure is high enough and the action is "stretchy" enough, the case will separate. In a Lee Enfield, for instance, you can load it hot and the case will stretch with each firing until it fails. If the case is lubricated, the case slides back and the shoulder moves forward when fired. Interestingly, with all else equal, the shoulder will move forward on the lubed case about the same amount as the dry case stretches as long as the pressure is sufficient to stretch the case. All of this has little to do with the original question of any discussion of thread fit.
In the end, a lot of gunsmiths, regardless of their field of interest, will have a tendency to want to blow smoke and feed potential customers a line of BS. Many will proclaim their methods and techniques to be unique and be the pinnacle of gunsmithing achievement and will stoutly claim no other capable of matching their performance. They will ignore the fact that, at the last match, they were beaten by two dozen amateurs who used different techniques altogether. WH

 

[alinwa]

That's not entirely true. The case will contain the pressure within a fairly narrow parameter. Pressure has to be sufficient to allow the case to grip the chamber wall but low enough that backthrust does not exceed the elastic limit of the brass. Now, it doesn't take much pressure for the head of the case to deflect, if only very slightly. Since a front locking action will deflect very little, the grip of the case on the chamber wall is of no consequence. If pressure is high enough and the action is "stretchy" enough, the case will separate. In a Lee Enfield, for instance, you can load it hot and the case will stretch with each firing until it fails. If the case is lubricated, the case slides back and the shoulder moves forward when fired. Interestingly, with all else equal, the shoulder will move forward on the lubed case about the same amount as the dry case stretches as long as the pressure is sufficient to stretch the case. All of this has little to do with the original question of any discussion of thread fit.
In the end, a lot of gunsmiths, regardless of their field of interest, will have a tendency to want to blow smoke and feed potential customers a line of BS. Many will proclaim their methods and techniques to be unique and be the pinnacle of gunsmithing achievement and will stoutly claim no other capable of matching their performance. They will ignore the fact that, at the last match, they were beaten by two dozen amateurs who used different techniques altogether. WH

I'm not altogether sure what Mr Will is saying here, I THINK he's calling me out

So to make it easy...... I'm going on record as disagreeing with perty much the entire post. Safest that way.

 

[Will Henry]

Not at all, Al. I'm only adding to the conversation. You can agree or disagree with my assertions, as you wish, but I've done my share of testing too. The comment about the "smoke blowing" was directed at no one in particular but the entire trade, in general. You know it happens, in gunsmithing as in carpentry, engineering, tire sales, concrete mixing, house painting, and medicine. In other words, all trades and professions have a tendency to self-promote; sometimes fraudulently or with little regard for fact. I, myself, may have my own pet theories but I'm not much of a self-promoter because I am very cognizant of the fact that a whole bunch of guys beat me regularly and they don't do things anything like I do. Others are great self-promoters though. So it is that we have those who promote tight threads, loose threads, Spiraloc threads, square threads, or buttress threads. I kind of agree with the poster who said, "threads are threads". WH

 

[hogpatrol]

Ask twenty different machinists how to go about doing a job and you'll get twenty different answers and each will be the best method. Compound setting for threads? 29°, 29 1/2°, or 30°. Chase with the compound or straight in with the cross-slide? Both sides of the tool 30° or clearance on the trailing edge? Which technique yields the best barrel threads?

 

[Will Henry]

That's easy. 29 1/2 with no clearance on the trailing edge . WH

 

[hogpatrol]

That's easy. 29 1/2 with no clearance on the trailing edge . WH

Same setting but I like clearance on the back side. My way is better.