Engineering question:

[Pete Wass]

over the years, there has been a fair bit of discussion on here of the torque values to apply to barrels when tightening to receivers. last evening I looked at several charts and the charts all say to use hundreds of Ft LBS on bolts that size. Is there some other engineering qualifier that would give us sound values that aren't someone's guess and opinion?

For instance, I have a threaded Anschutz action with an .850-20 thread in it. Just look at what a thread charts says for bolts in that size range!

Pete

 

[Jerry H]

Those specs are to achieve a particular bolt stretch. Something you do not want to do with a RF chamber.

 

[Pete Wass]

I understand that of course

Those specs are to achieve a particular bolt stretch. Something you do not want to do with a RF chamber.

but I would like to fine something that math supports as to how tight rifle tenon threads should be, if a formula or chart like that exists.

Pete.

 

[Jerry H]

I have never heard of such a chart ever been published in 30+ years of CFBR shooting. For CF, you might read Frank Vaughn's book Rifle Accuracy facts. He covers this subject rather well. You mentioned RF specifically though, where part of the rifle bore is within the receiver ring, where over torquing could distort the bore. You can verify this yourself by slugging the barrel with various torque values. A .0001 bore increase can easily be felt while pushing a lead slug. With practice you might a feel as little as a .00005 change in diameter. Both are extremely difficult to actually measure. Lead distorts real easy against a micrometer contact. Pure lead bullets do not shoot as well when they go from tight to loose in the barrel and tend to lead foul more in the loose spots. At the receiver junction point with an over torqued barrel, you will likely encounter a bore diameter change that can be felt with a slug. After you experiment with this, you could be the first to publish a chart for barrel torque values for RF tenons.

 

[Boyd Allen]

At the end of the chapter devoted to the barrel/action joint Vaugn lists several reasons why the problems that he encountered would be much less of an issue for a typical short range CF benchrest rifle. He did his testing using a Remington 721 with what I believe was a chromoly , sporter contour barrel, with the rifle mounted in a machine rest. While I am certainly a fan of Vaughn's, I think that his test setup was flawed in one respect. Tying the rifle down as he did, preventing it from moving as it might when shot as it would normally would be, undoubtedly put more stress on the barrel/action joint. This is not to say that his comparisons were not useful, but that negative results may have been exaggerated somewhat. Of course we will not no this for sure until another test method has been devised and the same tests repeated. Getting to the issue of tightening rimfire barrels, it seems to me that if he was of the opinion that there was less of a chance that CF benchrest rifles would have a problem, then the chance of a rimfire rifle having one would be substantially less.

 

[Jerry H]

I believe Vaughn was concerned with joint motion under the stress of firing. Certainly a less likely issue in RF. IMO, the RF barrel is much less tolerant of bore variation than a CF that has lots of pressure to work with.

 

[Pete Wass]

What I am interested in learning

I believe Vaughn was concerned with joint motion under the stress of firing. Certainly a less likely issue in RF. IMO, the RF barrel is much less tolerant of bore variation than a CF that has lots of pressure to work with.

is a safe, specific torque value for my Rimfire barrels. Safe in that the barrels will stay in place and yet not over stress anything. For instance, I use to torque my 30 cal barrels to 50 Ft Lbs, using a flat bar wrench with a hex head on it. I chose 50 because it seemed well within the charts for those sized threaded tenons and I wanted to always do each barrel the same. I never saw any adverse effects from 50 ft lbs.

I have seen pictures on here where some folks apply masking tape to both the action and barrel, draw a line and tighten to a specific measurement. I know well enough that 50 Ft lbs is way too much torque for these puny little RF rifles but what specific torque value is right for them? I plan to make hex or perhaps square head wrenches for them and would like to be able to tighten each one to the correct, measured amount of torque.

Thanks,

Pete

 

[Jerry H]

When I experimented with this on a .750 x 16 tenon, I felt 35 ft/lbs may be too much torque. I settled on 25 as a maximum based on the slug tests. Your larger diameter tenon will take more torque to stretch the bore. How much, I do not know. Note that the barrel will take more torque to break loose after it has been shot awhile. I never could determine a minimum based on how the rifle shot. I settled on 20 as a minimum for my rifle. My PPC barrels 1.062 x 18 were always torqued to 75-80 ft/lbs but I usually shot them very hot. 60-65K psi. RFBR is usually a quarter of that peak pressure.

I made some of these for RF since I could not find any. People don't switch barrels very often like they do in CF. It has different heads for the bolt diameter and an aluminum safety lug for thin walled actions.

 

[Boyd Allen]

Some years back I was speaking with a nationally known gunsmith about how to best deal with a pressed and pinned situation on a rimfire rifle (540X Remington) He told me that for some situations he had found that preparing the joint and using epoxy worked well when he wanted to do a small setback on a match (prone/position) rifle. It might be interesting to take this approach on a bench rifle. For something like a 40X you could make an adapter that was properly threaded, with a smooth bore for the barrel tenon. The adapter could be torqued in place and the barrel epoxied in afterwords. There would be plenty of area for an adhesive joint and the stress on the bore should be nil. I took the gunsmith's suggestion for setting back the 540X barrel and although I have not fired it a lot, it never gave any indication of barrel/receiver joint instability. We left the surfaces rough and degreased them.

 

[linekin]

Pete, I have no idea how much torque I put on my barrels but what I do is thread the action till the shoulders meet. Back the action off 1/4 turn & with a quick snap wind it back in place. It never comes loose & is never hard to remove at a later date. I'm gonna guess its somewhere under 20 ft. lbs.
I was told that either old model A or T manuals never used torque specs. They specified the length of wrench I guess figuring the average man would get about X torque from a 10" wrench.
USE A SHORT WRENCH!!!

Keith

 

[linekin]

Some years back I was speaking with a nationally known gunsmith about how to best deal with a pressed and pinned situation on a rimfire rifle (540X Remington) He told me that for some situations he had found that preparing the joint and using epoxy worked well when he wanted to do a small setback on a match (prone/position) rifle. It might be interesting to take this approach on a bench rifle. For something like a 40X you could make an adapter that was properly threaded, with a smooth bore for the barrel tenon. The adapter could be torqued in place and the barrel epoxied in afterwords. There would be plenty of area for an adhesive joint and the stress on the bore should be nil. I took the gunsmith's suggestion for setting back the 540X barrel and although I have not fired it a lot, it never gave any indication of barrel/receiver joint instability. We left the surfaces rough and degreased them.

Interesting.....

 

[Steve Kostanich]

I had a chat with Carl Kenyon back in the '90's, when he was still doing a fair amout of rimfire 'smithing. His method of rebarreling a pinned Anschutz barrel was to sweat solder the new barrel back into the receiver. He would tin all the contact surfaces and then somehow got everything lined up in a lathe and used the tailstock to push the action onto the barrel tennon when the heat of the contact surfaces came up to flow themprature. Might be why his 3 and 4 position match rifles shot so well.

Steve Kostanich

 

[JerrySharrett]

A few years ago there was an article in PS mag about just snapping the barrel to the action. Wrong, IMO. On a CF barrel with good quality threads on the new barrel about 75-150 lb/ft will do the job. In CF or RF the object is to create a joint that does not move but does not distort the precisionly machined assembly.


EDIT, I have a 10.5# rimfire built on a 94 Sako that Bill Myers built for his wife Inez. It has a split joint on the action hat allows adjustment of the headspace which is very important in RF.


.

 

[crb]

. For something like a 40X you could make an adapter that was properly threaded, with a smooth bore for the barrel tenon. The adapter could be torqued in place and the barrel epoxied in afterwords. .

I have done this with one 40X bbl. I also used a PacNor nut instead of a torque shoulder so I can adj the headspace easily. Unfortunately the bbl was a bit of an unknown and didn't shoot up to snuff even after messing with the leade and redoing the crown which has always worked in the past.

 

[Pete Wass]

Thanks Jerry

When I experimented with this on a .750 x 16 tenon, I felt 35 ft/lbs may be too much torque. I settled on 25 as a maximum based on the slug tests. Your larger diameter tenon will take more torque to stretch the bore. How much, I do not know. Note that the barrel will take more torque to break loose after it has been shot awhile. I never could determine a minimum based on how the rifle shot. I settled on 20 as a minimum for my rifle. My PPC barrels 1.062 x 18 were always torqued to 75-80 ft/lbs but I usually shot them very hot. 60-65K psi. RFBR is usually a quarter of that peak pressure.

I made some of these for RF since I could not find any. People don't switch barrels very often like they do in CF. It has different heads for the bolt diameter and an aluminum safety lug for thin walled actions.

View attachment 19786

This is very much the same wrench I had in mind. Before I read this, I had settled on 10 Ft Lbs as a beginning point . I appreciate your reporting on what you have done and I will use the 20 going forward. I was pretty certain folks had gone down this road and had hoped for help so that I wouldn't have to spend a lot of time "sperimentin". I don't have a lot of it left .

Thanks again,

Pete

 

[Pete Wass]

The Anschutz I have

Some years back I was speaking with a nationally known gunsmith about how to best deal with a pressed and pinned situation on a rimfire rifle (540X Remington) He told me that for some situations he had found that preparing the joint and using epoxy worked well when he wanted to do a small setback on a match (prone/position) rifle. It might be interesting to take this approach on a bench rifle. For something like a 40X you could make an adapter that was properly threaded, with a smooth bore for the barrel tenon. The adapter could be torqued in place and the barrel epoxied in afterwords. There would be plenty of area for an adhesive joint and the stress on the bore should be nil. I took the gunsmith's suggestion for setting back the 540X barrel and although I have not fired it a lot, it never gave any indication of barrel/receiver joint instability. We left the surfaces rough and degreased them.

came to me with a glued or I suppose Epoxied barrel -receiver joint. After threading the action, I lightly shrunk and loctited a bushing on the barrel and fit it to the action. Of course a number of things changed, like the chamber went from a big jam to the bullet just touching the lead and a new connection but the rifle shoots a little better now than it did before. Still not good enough to be competitive, in my opinion. ( this is a barrel fit before the Dog Knots came into being) I have another barrel I am going to fit to it if I get a chance this week. The "Glued" joint was a loosish fit, I thought.Guess if I were going that route I would go a light press fit with the appropriate LocTite. The sleeve I made is a - .0005"fit with the Green.I trust it to not shoot loose.I heated it with a hot aid gun briefly before I pressed it on.

Applying a lot of heat to guns, generally, unnerves me. I would never consider sweating a barrel on, too much of a klutz, me.

Pete

 

[Jerry H]

Pete, your mailbox is full. These are all that are left. $125 dual head, $100 single head. They are for changing barrels and not for removing factory installed barrels.

 

[Pete Wass]

Thanks,

Pete, your mailbox is full. These are all that are left. $125 dual head, $100 single head. They are for changing barrels and not for removing factory installed barrels.
View attachment 19787

I'll empty it.

Thanks,

Pete

 

[Mozella]

...... snip............For instance, I have a threaded Anschutz action with an .850-20 thread in it. Just look at what a thread charts says for bolts in that size range!

Pete

The short answer is that a barrel is not a bolt.

Think about it. The shank end of the barrel has to have a certain diameter to accommodate the chamber plus enough material to provide enough stiffness and thermal mass to ensure good accuracy. So, in the case of the rifles most of us shoot, the threads are usually somewhere close to an inch in diameter, smaller for small caliber or hunting guns, larger for large caliber target guns.

If you look at the recommended torque values for bolts of that diameter, the values are huge compared to what most of us have ever used for anything including guns, automobiles, etc. So unless you work in an oil field or something like that, you'll never have a need to torque a 1" bolt to 300 ft pounds and even perhaps as high as 1000 ft pounds. That's a lot of torque and entirely appropriate for a big bolt. But not appropriate in any way for a gun barrel.

Said another way, just because the threaded cap for your mayonnaise jar is 4" in diameter doesn't mean you should torque it to 65,000 ft pounds. Why? Because mayonnaise isn't a bolt either.

 

[Pete Wass]

If you re read

The short answer is that a barrel is not a bolt.

Think about it. The shank end of the barrel has to have a certain diameter to accommodate the chamber plus enough material to provide enough stiffness and thermal mass to ensure good accuracy. So, in the case of the rifles most of us shoot, the threads are usually somewhere close to an inch in diameter, smaller for small caliber or hunting guns, larger for large caliber target guns.

If you look at the recommended torque values for bolts of that diameter, the values are huge compared to what most of us have ever used for anything including guns, automobiles, etc. So unless you work in an oil field or something like that, you'll never have a need to torque a 1" bolt to 300 ft pounds and even perhaps as high as 1000 ft pounds. That's a lot of torque and entirely appropriate for a big bolt. But not appropriate in any way for a gun barrel.

Said another way, just because the threaded cap for your mayonnaise jar is 4" in diameter doesn't mean you should torque it to 65,000 ft pounds. Why? Because mayonnaise isn't a bolt either.

My second post, I asked is there was some sort of rule or, I don't really know what word to use but believed there must be some way to factually quantify what is the right torque for these circumstances. Perhaps this situation has not been explored by engineers who designed rifles, I don't know and why I asked the question here thinking there may be folk who knew for sure using math to say X is the answer and here is the proof. One would think, considering the "Liability issues" of gun manufacturing, this area would have been, explored, developed and published.

Anyway, I like to discuss these sort of things so thanks everyone for participating.

Pete