Barrel TQ and Headspace Crush Measurements

[DaveTooley]

I may of had others come through the shop but I did see one Sako where the barrel was noticeably bulged on the shoulder from over tightening. I doubt it took 500 ft/lbs to do that as it didn't have much of a shoulder. A 3/4" drive torque wrench is over 48" long. How do you not twist the action?

 

[jackieschmidt]

Do these bolts ever need to come off? If so, can they be used again?

There might be a little confusion as to what is meant by “torque to yield” and the tightening of a bolt using some type of tool to actually measure the amount of stretch you are imparting on the length of the bolt in order to insure that it is imparting the proper tension on the joint.

Torque to yield bolts are specifically manufactured so that they are installed in an exacting procedure. You are using a predetermined amount of torque on the bolt so that it reaches but does not exceed the action manufactured yield strength of the fastener but approaches it. These fasteners are generally used in applications where production line necessities dictate that all of the fasteners have an equal pull down force and are installed with a very controlled process.
A good example is the assembly of a large truck frame. Most of the bolts used are torque to yield because they will never be removed during the life of the vehicle and have to be installed correctly. This installation might include a specific lubricant.

In an application where you are measuring the stretch of a fastener to insure that it is indeed exerting the proper tension in a joint, the actual measured torque is a non issue. In this application, you are not approaching the actual yield strength of the fastener’s material. You are simply insuring that the fastener is indeed imparting the proper holding force on the joint.

A example is how we tighten rod bolts in performance engines. The manufacturer will give you both a torque figure and a stretch measurement, say .007 inch. You first torque the fastener to the correct number, and measure the stretch. If it does stretch .007, fine. However, if it does not, you then add torque until it does.



The reason this is important is because the torque figure has nothing to do with the actual tension that the fastener is imparting on the joint, because other things, such as thread quality, lubrication, and even variations in material strength can give you a false reading. Keep in mind, this is NOT a fastener that was specifically designed as a “torque to yield” fastener. This type of fastener will come back to it’s original configuration, (length) when loosened.

that is why you can reuse it.

When you actually verify that you did indeed “stretch” the fastener, you can feel assured that it is imparting the correct amount of tension on the joint.

 

[Dusty Stevens]

There might be a little confusion as to what is meant by “torque to yield” and the tightening of a bolt using some type of tool to actually measure the amount of stretch you are imparting on the length of the bolt in order to insure that it is imparting the proper tension on the joint.

Torque to yield bolts are specifically manufactured so that they are installed in an exacting procedure. You are using a predetermined amount of torque on the bolt so that it reaches but does not exceed the action manufactured yield strength of the fastener but approaches it. These fasteners are generally used in applications where production line necessities dictate that all of the fasteners have an equal pull down force and are installed with a very controlled process.
A good example is the assembly of a large truck frame. Most of the bolts used are torque to yield because they will never be removed during the life of the vehicle and have to be installed correctly. This installation might include a specific lubricant.

In an application where you are measuring the stretch of a fastener to insure that it is indeed exerting the proper tension in a joint, the actual measured torque is a non issue. In this application, you are not approaching the actual yield strength of the fastener’s material. You are simply insuring that the fastener is indeed imparting the proper holding force on the joint.

A example is how we tighten rod bolts in performance engines. The manufacturer will give you both a torque figure and a stretch measurement, say .007 inch. You first torque the fastener to the correct number, and measure the stretch. If it does stretch .007, fine. However, if it does not, you then add torque until it does.



The reason this is important is because the torque figure has nothing to do with the actual tension that the fastener is imparting on the joint, because other things, such as thread quality, lubrication, and even variations in material strength can give you a false reading. Keep in mind, this is NOT a fastener that was specifically designed as a “torque to yield” fastener. This type of fastener will come back to it’s original configuration, (length) when loosened.

that is why you can reuse it.

When you actually verify that you did indeed “stretch” the fastener, you can feel assured that it is imparting the correct amount of tension on the joint.

With bolt stretchers on turbines, you put the nut on there (usually with a hoist) then install the bolt stretcher. It pulls the bolt a certain amount then you hand tighten the nut and back off the stretcher. Torque is determined by the stretch you put on it. Riverhawk was the brand i had schooling on. Ive seen them down in engine rooms on boats so i figure youve seen em in use

 

[jackieschmidt]

With bolt stretchers on turbines, you put the nut on there (usually with a hoist) then install the bolt stretcher. It pulls the bolt a certain amount then you hand tighten the nut and back off the stretcher. Torque is determined by the stretch you put on it. Riverhawk was the brand i had schooling on. Ive seen them down in engine rooms on boats so i figure youve seen em in use

Dusty, several large diesel manufactures install heads in that manner.

for instance, Nohab typically will have five head bolts that hold each head in place. They have head bolts specifically designed to be use with as special spinner nut and a pack of five hydraulic jacks that stretch all five bolts at the same time. The nuts are run down snd simply firmly seated. The jacks are then released,

to remove the heads, the procedure is simply reversed.

 

[Deleted Dewey]

“When attaching the barrel to the action, Tactical Operations again uses their own unique process which involves using torque settings of 500 ft-lbs. They originally used 150-180 ft-lbs, but then upped that to 250 after a while. They then discovered that they could reduce cold bore shot movement if they went to 500 ft-lbs which is what they do.”

I guess over torquing is easier that making everything square, concentric and well-finished. I'm also a bit dubious about that number, that much torque would surely fail either the threads or the shoulder? But then, the name of the outfit itself would give me pause.

 

[tom]

Does federal make BRA ammo?

Tom

 

[Tokay444]

Youd have to take some off the cone end once it stretches that far. Im still floored by this market cornering of the zero and ones shooting factory gold medal 308/168 for $7000. It has really messed up my mind.

I have Mike’s phone number if you’d like to call him. He’s very open to communication and enjoys sharing his story.

 

[Tokay444]

Do these bolts ever need to come off? If so, can they be used again?

If they’re torque to yield, then no. They usually need to be replaced. Once in its plastic deformation state it’s not likely to take the same procedure a second time without necking and pulling apart.

 

[Dusty Stevens]

Dusty, several large diesel manufactures install heads in that manner.

for instance, Nohab typically will have five head bolts that hold each head in place. They have head bolts specifically designed to be use with as special spinner nut and a pack of five hydraulic jacks that stretch all five bolts at the same time. The nuts are run down snd simply firmly seated. The jacks are then released,

to remove the heads, the procedure is simply reversed.

Yes thats it. Mercury outboard heads do the torque to 45 then 1/4 turn or whatever

 

[SKWERLZ]

500 ft pounds is approaching grade 5 fine thread 1” bolt torque values.

I wonder how barrel steels compared to bolt steel grades.

 

[jackieschmidt]

One item that was brought up is Mike is using some form of a buttress thread

That means when he trues the action threads, he is machining the thread diameter out to a larger pitch diameter and then establishing a buttress thread in the action. A buttress thread is designed to take a load strictly in the linear plain in one direction and not exert force in the radial plain. As you can see in the diagram, it is square on the load carrying side and 45 egress on the clearance side.

while I have seen old military actions with square, or box threads, I can’t ever recall encountering a buttress thread in an action.

unlike a V thread, which is self centering, if a buttress is used to also center the barrel in the action, it has to be machined with a close major diameter in order to possess any radial centering of the pieces. It’s basic function is to achieve maximum strength in one direction.

One advantage of using this type of thread in a barrel tenon/action joint is you can use a high torque figure without distorting the chamber or the action body since unlike a V thread, it does not induce radial load.

 

[jackieschmidt]

500 ft pounds is approaching grade 5 fine thread 1” bolt torque values.

I wonder how barrel steels compared to bolt steel grades.

416R stainless at 28 RC actually has (on paper), about the same tensil and yield strength as a typical grade five bolt. Keep in mind, grade 5, or any grade of a bolt, is a specification, not an actual material.

 

[Doug Beach]

I use 600 lbs. This way, I don’t even have to use Fed. Match. Yard sale Cor-Lokts shoot bugholes all day long, if I do my…. Never mind.

 

[rijndael]

One item that was brought up is Mike is using some form of a buttress thread

How is that different from a spiralock thread?

 

[jackieschmidt]

How is that different from a spiralock thread?

The spiralock is touted as having a “self locking feature”.
I personally think it is at best a solution to a non existing problem.

 

[Alex Wheeler]

The idea is to deform the thread crest to distribute load across more threads. That may be true. But does it effect rifle accuracy? I am sure I know the book this idea came from. Keep in mind the rifle used for that testing was a rem 721 in .270 win. Not a br rifle. There are other ways to accomplish the same goal but in my opinion the shoulder is what matters, not the threads.

 

[3Sigma]

There might be a little confusion as to what is meant by “torque to yield” and the tightening of a bolt using some type of tool to actually measure the amount of stretch you are imparting on the length of the bolt in order to insure that it is imparting the proper tension on the joint.

Torque to yield bolts are specifically manufactured so that they are installed in an exacting procedure. You are using a predetermined amount of torque on the bolt so that it reaches but does not exceed the action manufactured yield strength of the fastener but approaches it. These fasteners are generally used in applications where production line necessities dictate that all of the fasteners have an equal pull down force and are installed with a very controlled process.
A good example is the assembly of a large truck frame. Most of the bolts used are torque to yield because they will never be removed during the life of the vehicle and have to be installed correctly. This installation might include a specific lubricant.

In an application where you are measuring the stretch of a fastener to insure that it is indeed exerting the proper tension in a joint, the actual measured torque is a non issue. In this application, you are not approaching the actual yield strength of the fastener’s material. You are simply insuring that the fastener is indeed imparting the proper holding force on the joint.

A example is how we tighten rod bolts in performance engines. The manufacturer will give you both a torque figure and a stretch measurement, say .007 inch. You first torque the fastener to the correct number, and measure the stretch. If it does stretch .007, fine. However, if it does not, you then add torque until it does.



The reason this is important is because the torque figure has nothing to do with the actual tension that the fastener is imparting on the joint, because other things, such as thread quality, lubrication, and even variations in material strength can give you a false reading. Keep in mind, this is NOT a fastener that was specifically designed as a “torque to yield” fastener. This type of fastener will come back to it’s original configuration, (length) when loosened.

that is why you can reuse it.

When you actually verify that you did indeed “stretch” the fastener, you can feel assured that it is imparting the correct amount of tension on the joint.

Another reason for the torque to yield or torque to strain is to guarantee a specific bolt preload. This means the load and fatigue calculations done in design and test actually are accurate.

1.0625 x 16 threads can easily handle 500 ft-lbs, depending on lubricant and material. These size of threaded joints are often torqued to these levels in industry (piping and pressure vessels).

As others have mentioned, we only set the faces and threads together at 50 to 100 ft-lbs. I haven't run the numbers, but I bet the threads are barely loading up. I would think a face load between the action and barrel (or "washer" aka recoil lug) is most critical, With a target in the 10 to 15 ksi zone for seat stress.

As for buttress threads... way overkill, but 500 ft-lbs it isn't gonna hurt anything if done well. Just really difficult to get right and hold the tolerance needed for this level of precision. Lots of designs out there (ACME, proprietary designs), and few standards. Seems like a solution looking for a problem.

But, my experience with those is in the oil and gas world and high pressure vessel design. Also spent 8 years in engineering development in heavy diesel, off highway, and commercial trucks before my current gig.

 

[xr650rRider]

Lot of studies completed in oilfield applications determined that up to 92% of applied torque was taken up by friction. Circumferential displacement is the API recommended practice for making up the joint. Sucker rod manufacturers supply torque cards that measures torque purely based on displacement. A 1" rod pin is cleaned and a special lubricant applied and then connection made up by hand. Depends on rod class but displacement value from bumped up hand tight to torqued can be 23/32". The torque is nearly 1000 ft/lbs. Since crews have been using this method, rod failures at connections are greatly reduced. So maybe this gun manufacturer/gunsmith worked on a well service rig.

 

[jackieschmidt]

Another reason for the torque to yield or torque to strain is to guarantee a specific bolt preload. This means the load and fatigue calculations done in design and test actually are accurate.

1.0625 x 16 threads can easily handle 500 ft-lbs, depending on lubricant and material. These size of threaded joints are often torqued to these levels in industry (piping and pressure vessels).

As others have mentioned, we only set the faces and threads together at 50 to 100 ft-lbs. I haven't run the numbers, but I bet the threads are barely loading up. I would think a face load between the action and barrel (or "washer" aka recoil lug) is most critical, With a target in the 10 to 15 ksi zone for seat stress.

As for buttress threads... way overkill, but 500 ft-lbs it isn't gonna hurt anything if done well. Just really difficult to get right and hold the tolerance needed for this level of precision. Lots of designs out there (ACME, proprietary designs), and few standards. Seems like a solution looking for a problem.

But, my experience with those is in the oil and gas world and high pressure vessel design. Also spent 8 years in engineering development in heavy diesel, off highway, and commercial trucks before my current gig.

In all of my years in the Machine Shop business, I have only encountered one Buttress thread.
About 10 years ago, one of our shipyard customers docked a 6000 hp single screw harbor tug to change out the propeller. The thing was built back in the ‘50’s and had been refurbished and repowered several times.

The propeller shaft was 14 inches in diameter. The prop taper had a 10 inch diameter 2 TPI left hand buttress thread that secured the prop.The shipyard had no idea it was a left hand thread, finally gave up on breaking It loose and ended up cutting the nut, which was around 18 inches in diameter, in half with an arc gouge.

When they called me out to look at it, I discovered that it was a left hand buttress thread.

We ordered a piece of material and I made the nut, which finished weighed around 150 pounds.

It’s the only buttress I have ever cut. I ground the tool to cut the thread from a piece of 1” square Rex-95 tool steel.

 

[Dusty Stevens]

In all of my years in the Machine Shop business, I have only encountered one Buttress thread.
About 10 years ago, one of our shipyard customers docked a 6000 hp single screw harbor tug to change out the propeller. The thing was built back in the ‘50’s and had been refurbished and repowered several times.

The propeller shaft was 14 inches in diameter. The prop taper had a 10 inch diameter 2 TPI left hand buttress thread that secured the prop.The shipyard had no idea it was a left hand thread, finally gave up on breaking It loose and ended up cutting the nut, which was around 18 inches in diameter, in half with an arc gouge.

When they called me out to look at it, I discovered that it was a left hand buttress thread.

We ordered a piece of material and I made the nut, which finished weighed around 150 pounds.

It’s the only buttress I have ever cut. I ground the tool to cut the thread from a piece of 1” square Rex-95 tool steel.

Sounds like the perfect job for a south bend 9 or one of those harbor freight mini lathes