Gunsmithing Tools needed for Shouldered barrel swap

[CShooter92]

Looking to purchase a new barrel or two for my Surgeon 591. I'd have them shouldered up to my action by my gunsmith. What tools are all required for at home barrel swaps?

Action wrench? What kind?
Barrel Vise? brand?
Anything else?

 

[ken226]

A set of go and no-go gauges. You can mark the position of the barrel in the action for correct headspace' but verify with gauges.

A peice of leather to pad your barrel and receiver in the vises. Expect some finish damage anyway, but minimize it with some padding.

A solid table to mount your receiver vise. Factory barrels can have a couple hundred lbft of torque.

Personally, i prefer to wear out a barrel before replacing it. But i keep my guns cerakoted and swappin barrels usually leaves marks.
But if your cool with that, the tools you listed + my recommendations should get you by.

 

[Sheldon N]

I've never needed go or no-go gauges for shouldered barrels. It's not like you can do anything to change headspace anyways, other than call your gunsmith and say "You're incompetent" if the barrel didn't headspace correctly.

To prevent barrel marking I'll just wrap the barrel in a piece of scrap cardboard.

If you plan to swap barrels constantly sharing the same action, check out the Ross Vise. No action wrench needed, just run lower torque values and swap with the gun still in the stock. If you have a barrel on that has high torque values, you may need an action wrench though.

 

[ken226]

The torque value used installing the barrel changes the headspace.

Once the barrel is torqued, has the correct headspace, and its position is marked, there wouldnt be a need for gauges.

The gauges may not be necessary in many cases, but they are cheap insurance.

 

[Sheldon N]

If you're having to attempt to use torque to fix headspace, something has gone wrong with your gunsmith. The difference between a light 30 ft/lb torque value and a beefy 100 ft/lb is maybe a thou or two. If it's wrong enough to be dangerous, spinning it on tighter isn't going to fix it.

The only reason an end user would need a go-gauge for a shouldered barrel is because they don't trust their gunsmith to cut the chamber correctly.

 

[ken226]

Im not suggesting that anyone change torque to adjust headspace.

Im suggesting that if someone has a barrel vise and action wrench, and loses the markings that indicate where the pre-headspaced barrel should be torqued to, they may be better off already having a set of headspace gauges.


In the hundreds of barrels ive chambered and installed, ive seen significantly more than a couple thousandths.

From hand tight to 70 lb ft changes it about .006" on Remingtons, a little less on Winchesters and Howas. The headspace will also change over time, with repeated barrel removal / install operations. But, likely most people wouldnt swap barrels often enough to see a significant change.

Im not saying that gauges are necessary. Just that they are a good thing to have.

You do it however you please.

When i make recommendations for customers who have similar ideas. I recommend that they keep some gauges on hand. Its not a requirement, just a recommendation.

The OP can choose your advice or mine and likely be fine either way. If the extra hundred dollar cost of a gauge set means his kids dont get to eat, he's better off without them.

 

[DAVETOOLEY]

I've done hundreds of barrels for a 591. They all HS within .0015" No gages needed
No need for witness marks. Barrel vise, action wrench, common sense is all that's needed
Clamp barrel
break action loose
Clean action face lube barrel threads
screw barrel in
A good grunt on the action wrench will get you to 75-90 Ft/lbs. That's all that's needed
That's it in a nutshell.
powdered rosin and heavy target paper work great inside bushings
If you can change a light bulb you can change a barrel.

 

[Rubicon Precision]

When I fit a barrel, I torque it, break it loose and torque it again then do the markings and finish work. The next time it goes on the receiver, I bet there is less than a couple/few degrees of turn between 50 and 100 ft lbs of torque. Even at a generous 10 degrees, that's .0017" of HS difference on a 16tpi thread (perfect world, not counting stretch and where and how it happens). I haven't checked, but it wouldn't surprise me if there is close to that much variation between manufacturers and lots of gauges.

Bottom line is If your (trustworthy) smith fit the barrel to you actual action, there should be no need for HS gauges.

 

[ken226]

Theres about .0015 difference between my ptg and clymer gauges.

The difference between my PTG go an no-go gauges is .004.

If a barrel was chambered to the center of the go and no-go, 10° or .0017 in either direction would still be within spec.

If the chamber was cut somewhere outside of that center, lets say short or long, .001 away from the limit either way, the 10° could put it out of spec. But, 10° would be about the difference between hand tight and 100 lb ft.

If he gets it to within 25 lb-ft above or below the torque it was headspaced at, he can save the hundred bucks on gauges and buy ammo instead.

Anyone should be able to get that close.

 

[BootyLord]

 

[jetmd]

Im not suggesting that anyone change torque to adjust headspace.

Im suggesting that if someone has a barrel vise and action wrench, and loses the markings that indicate where the pre-headspaced barrel should be torqued to, they may be better off already having a set of headspace gauges.


In the hundreds of barrels ive chambered and installed, ive seen significantly more than a couple thousandths.

From hand tight to 70 lb ft changes it about .006" on Remingtons, a little less on Winchesters and Howas. The headspace will also change over time, with repeated barrel removal / install operations. But, likely most people wouldnt swap barrels often enough to see a significant change.

Im not saying that gauges are necessary. Just that they are a good thing to have.

You do it however you please.

When i make recommendations for customers who have similar ideas. I recommend that they keep some gauges on hand. Its not a requirement, just a recommendation.

The OP can choose your advice or mine and likely be fine either way. If the extra hundred dollar cost of a gauge set means his kids dont get to eat, he's better off without them.

The gauges or the kids?

 

[ken226]

When I fit a barrel, I torque it, break it loose and torque it again then do the markings and finish work. The next time it goes on the receiver, I bet there is less than a couple/few degrees of turn between 50 and 100 ft lbs of torque. Even at a generous 10 degrees, that's .0017" of HS difference on a 16tpi thread (perfect world, not counting stretch and where and how it happens). I haven't checked, but it wouldn't surprise me if there is close to that much variation between manufacturers and lots of gauges.

Bottom line is If your (trustworthy) smith fit the barrel to you actual action, there should be no need for HS gauges.

The stretch itself, mostly compression in the front part of the receiver and tension in the barrel tenon, is what causes the headspace dimension change.

When the barrel shoulder contacts the receiver face, further rotation puts the barrel tenon in tension which tends to decrease the headspace in an amount appx proportional to ((1/thread pitch) / 360) x degrees of rotation.

Further, the barrel tenon threads pull the actions threads toward the shoulder, putting the threaded portion of the receiver in compression. Also about proportional to ((1/thread pitch) / 360) x degrees of rotation. This also tends to decrease the headspace.

The two effects taken together tend to change the measured value from what one would expect just by calculating that change due to 1 divided by pitch divided by 360 x degrees of rotation. Its also slightly changed, though not significantly, by thread deflection in the direction of shear.

The pros here are almost certainly right in that gauges are normally not necessary, but for someone who's new to swapping barrels, and likely doing this for the first time ever, i stand by my recommendation that they use a measuring tool to check their work.

But, its just a recommendation, im not suggesting that anyone here is wrong.

 

[Rubicon Precision]

My head space is in spec hand tight and at 100 ft lbs. I am sure it would still be in spec at 200 ft lbs. I'm not concerned about a customer changing a barrel I fit for their action with or without HS gauges.

 

[DAVETOOLEY]

Ditto here. In 35 years of smithing I have never had the headspace change a significant amount when a barrel is torqued to spec. When the customer is looking over my shoulder I stop .0005" short so the bolt drags on the go gage while still in the lathe. It will still close after the barrel is torqued to 70 Ft/lbs.
Measure small and cut small with solid machine practices . Anyone having to do otherwise should question their process.

 

[ken226]

I'm a bit OCD about double checking and probably spend too much time checking the minutia of every detail.

If people listened to me they'd spen an hour on a 10 minute job.

You guys likely do this way more than i and have a good edge in efficiency.

 

[DAVETOOLEY]

I'm a bit OCD about double checking and probably spend too much time checking the minutia of every detail.

If people listened to me they'd spen an hour on a 10 minute job.

You guys likely do this way more than i and have a good edge in efficiency.

Didn't intend to bust your balls but I've heard that HS changes when torquing a barrel on for decades. It doesn't pass the sniff test. If there are no other factors in play , as soon as the shoulders make contact HS can't change. Radial orientation to a point then that quickly goes away. Using hand tools there is no way we can distort/deform displace metal.

 

[ken226]

Its no problem, i dont take it as having my balls busted. I enjoy discussion, and occasionally learn something.

Your saying that you get the same headspace measurements at the point that the shoulder makes contact that you get when the barrel is torqued to the final value?

I certainly don't. After i finish a chamber,
barrel still on the lathe, and thread the action onto the barrel tenon, if i tighten the action to several ft-lbs, and with a headspace that allows a go gauge to just fit but does not chamber the no-go,

if i then take the barrel off the lathe, put it in a vise, and torque the barrel to 70 ft-lbs, the go gauge will no longer chamber.

I tried this many times, taking measurements every time to determine how much deeper to cut the chambers on the lathe, so that they arrive at the correct headspace when torqued.

I need to cut most of my chambers about .003 deeper on the lathe, to arrive at the center of my go / no-go .004 tolerance.

Granted, this isn't on Surgeons but on Remingtons. On Howas and Winchesters i sometimes, before i got the numbers dialed in, had to hand ream the chamber another .001-.002 to hit the center of the headspace tolerance.

But, the value most definitely, measurably changes, for me, from a low torque value to a high one.

Please dont take my words as argument, that isn't my intent. Im genuinely interested in how we get different results.

I used Hooke's law from one of my old college textbooks to help develop my process.

Here it is. The effective bolt enlongation formulas. Engineers edge has it a bit down the page:

https://www.engineersedge.com/calculators/bolt_elongation_14608.htm

The calculated stretch doesn't match up perfectly to my experience though. According to Hooke's law stress strain enlongation formula, i should actually be seeing a significantly bigger change in headspace than im actually getting.


But, barrels aren't bolts, though im using the correct values for tensile stress area, youngs modulus (using 200mpa or 20007 psi^2), pitch, length, etc.

But, experience tends to trump academics every time, so your experience has value to me.

I got into gunsmithing as a hobby, but my experience and education is mostly in design engineering and CNC programming. Im still gaining experience to go with the academics.

 

[ken226]

On further thought and some review, i think the reason Hooke's law enlongation method predicts a value that is higher than what i actually see is because the stress area in highest tension is in the threaded portion of the chamber, around the area of the chamber about 3/4"-1" forward of the breech face, or about the rear face of the recoil lug.

The tension at the chambers shoulder datum would be significantly less. When i change the length value to = the distance from the breechface to the shoulder datum, i get about the same enlongation value that im seeing in practice.

Perhaps my problem is that i'm spending an inordinate amount of effort aiming for the center of that .004 go/no-go range and worrying about nothing?



It makes perfect sense now. If i cut the chamber to the minumum depth on the lathe to chamber the go gauge, the Hooke's law formula precisely predicts the amount by which the go gauge no longer chambers after torquing to 70 lb-ft.

If i go .002"-.004 or deeper than the minimum when the receiver is hand tight, ill be at about .0005"-.001" past minimum when torqued to 70 ft-lb or 4600lbs axial stress applied over .5^2pi-.237^2pi x 2"

At a Youngs modulus of 200mpa, a stress area of .5^2pi-.237^2pi x 2, and applied tensile load of 4600lbs, i get the appropriate outputs to make sense of it.

If i'd taken into account the stress length x area in stress to the shoulder datum rather than the just the tenon, i could have skipped all the trial and error stuff.



Thanks for the insight guys, its very much appreciated.

 

[DAVETOOLEY]

Ken226

Give me a call and we can talk about your process. There's always the chance of self inflicted problems ,particularly with factory actions.

704-864-7525 Shop
If i don't pick up leave a message and I'll get back to you.

 

[ken226]

Will do. Thanks Dave.

 

[CShooter92]

Is there any issues when swapping out a Carbon fiber barrel regularly? or any special precautions that should be taken?

 

[Sheldon N]

Is there any issues when swapping out a Carbon fiber barrel regularly? or any special precautions that should be taken?

My understanding is that you'd need to clamp onto the shank of the barrel where the metal is, not onto the carbon fiber. That means pulling the action from the stock, taking off the scope, etc. Much less easy to do regular barrel swaps than a steel barrel where you can clamp on anywhere and leave the scope on.