Cliff Grays Podcast with Aaron Davidson

[nm.otter]

discussion going on right now over at snipershide in a thread started by a guy saying 100 fl/lb tq on prefits is stupid and shouldn't need more than 35.

After reading all (and understanding most) of that, I'm not going to worry about Tikka prefits.

Also downloaded the Vaughn book for mid-winter reading.

 

[Klooop]

............

• Owner of PVA recommends 70 for standard bolt face and 100 for magnums and provided some calculations to justify it (responding to my questions that mimicked some in this thread). However, he indicated the pre-load with the above torque values exceeded the force of the rounds being fired.

Barrel Torque Ludicrocity

lol. Really though. 100ftlbs for prefit barrel torque? ****, I know this isn’t necessary. AR15 armorer schools is min 35ftlbs unless old school barrel nut needs advanced to next cut out for gas tube clearance. Then it’s 35-65ftlbs range. I run 55ftlbs on my bolt gun Savage style barrel nut...

www.snipershide.com

Those are the basic calcs I would expect to see, bolt preload as a function of applied torque. Then comparing to axial thrust from firing a round. Good stuff!

One thing I didnt see discussed is substantial variability in k-factor, torque uncertainty/error, etc. It is possible to have ~25%-35% preload variability for similar hardware, torqued to similar conditions. Ref NASA-STD-5020 for some additional fun reading on spaceflight fastening systems.

It's possible a lot of issues are simply a result of low nominal margin to separation on the preloaded joint. We always size fasteners to work at both min and max preload for a given torque.

Oh, and these barrel threads are nowhere close to anything other than normal localized yeilding...faster systems are frequently sized to 70% or 80% (or more) of yield for high cycle fatigue applications, which still keeps the overall faster in the elastic range.

I wouldn't have any concern torquing these barrels to a couple hundred ft-lbs as long as the tooling and resulting headspace can accommodate it. Galling would be a concern, too - especially for stainless joints.

Good discussion here. I need to read more into the posted book.

 

[Aaron Davidson]

If we assume that the joint moves, then we only need to consider how to get it to "tighten" back to center.

Thread finish is a factor. Scope base screw holes penetrating and interfering with the thread are a problem. If separate, recoil lug touching the barrel is an issue. Any touching of the barrel to the stock (or bedding).

When the joint comes loose, everything needs to be allowed to move naturally back the "center". The 60 deg thread does most of this, but if something causes a hitch, then its an issue.

Sidebar, this is why we started threading barrels with a CNC lathe 15 years ago. Surface finish....

 

[BBob]

Sidebar, this is why we started threading barrels with a CNC lathe 15 years ago. Surface finish....

While it may not be able to fully rival CNC some of us have put effort and $$$ into machining the best threads we can make on manual machines. Good equipment with a careful and repeatable setup with good inserted tooling (tested and purposefully selected) goes a long ways in achieving this. I can say I can hit repeatable barrel timing pretty easily when everything is the same or near same which wouldn’t happen if your technique and setup wasn’t good or repeatable. For the common action thread pitch’s I have pretty repeatable numbers for barrel rotation at various torques and am able to hit a small window of rotation when torquing a barrel. I’m sure you (Gunwerks) do too.

 

[Aaron Davidson]

While it may not be able to fully rival CNC some of us have put effort and $$$ into machining the best threads we can make on manual machines. Good equipment with a careful and repeatable setup with good inserted tooling (tested and purposefully selected) goes a long ways in achieving this. I can say I can hit repeatable barrel timing pretty easily when everything is the same or near same which wouldn’t happen if your technique and setup wasn’t good or repeatable. For the common action thread pitch’s I have pretty repeatable numbers for barrel rotation at various torques and am able to hit a small window of rotation when torquing a barrel. I’m sure you (Gunwerks) do too.

For sure. You have to have the right insert. Most are using inserts designed for the 1000 rpms you need to get the correctly calc'd surface speed at the 60 rpms a human can manage manually threading. The micro tearing result on the thread surface creates friction that can "stick" a barrel in an unusual position.

 

[Sundodger]

Great turn to the conversation guys.

What many people don’t realize is that as the assembly tq rises, more and more of your force is getting eaten up by friction. When you get to that 75% proof load that many of us are striving for, most of the force you are applying in tq is getting eaten up by friction (threads and under head). That causes a lot of noise in the torque tension relationship, which is the cause of a lot of joints coming apart even though they hit their specified tq. Anything you can do to pull friction out of the joint like good surface finish goes along way. The other approach is tq plus angle, which basically bypasses noisy joints, but not all joints are appropriate for that and I suspect the action to barrel is one of those.

 

[Sandstrom]

I have not done deep dive on the subject of barrel torque, however on some of the Tikka barrels that I have removed, I noticed some sort of thread locker. I would have to assume Tikka does nothing without some sort of reason, could thread locker be their solution to this potential problem?

Ryan

 

[BBob]

I have not done deep dive on the subject of barrel torque, however on some of the Tikka barrels that I have removed, I noticed some sort of thread locker. I would have to assume Tikka does nothing without some sort of reason, could thread locker be their solution to this potential problem?

Ryan

What version were they? Stainless? Stainless Cerakoted? Carbon steel blued? Lots of people over the years have said Remington used thread locker but what they more likely did was use a sealer of sorts to keep the bluing salts out of the joint. Maybe Tilka did the same if what you saw is on a carbon steel blued version.

 

[Sandstrom]

What version were they? Stainless? Stainless Cerakoted? Carbon steel blued? Lots of people over the years have said Remington used thread locker but what they most likely did was use a sealer of sorts to keep the bluing salts out of the joint. Maybe Tilka did the same if what you saw is on a carbon steel blued version.

They were all stainless. It appeared to be a black liquid, also, it did not appear to be evenly coated. I just snapped a picture of one of them.

For what it’s worth, this barrel has @20 rounds on it.
Ryan

 

[mxgsfmdpx]

I have not done deep dive on the subject of barrel torque, however on some of the Tikka barrels that I have removed, I noticed some sort of thread locker. I would have to assume Tikka does nothing without some sort of reason, could thread locker be their solution to this potential problem?

Ryan

It’s a light coating of anti-seize. It’s on all tikka and sakos just not always very noticeable.

 

[Sandstrom]

It’s a light coating of anti-seize. It’s on all tikka and sakos just not always very noticeable.

I am not necessarily disagreeing with you, only raising a few additional questions, as I have no clue what it is. If it was anti-seize, wouldn’t it have an even distribution?(for the life of me I can’t recall what the coverage looked like in the action.) Why would Tikka put anti-seize on something they definitely don’t want to loosen up? Also, every other thing in the world that I have taken apart with anti-seize is a million times easier than removing a Tikka barrel
Ryan

 

[mxgsfmdpx]

I am not necessarily disagreeing with you, only raising a few additional questions, as I have no clue what it is. If it was anti-seize, wouldn’t it have an even distribution?(for the life of me I can’t recall what the coverage looked like in the action.) Why would Tikka put anti-seize on something they definitely don’t want to loosen up? Also, every other thing in the world that I have taken apart with anti-seize is a million times easier than removing a Tikka barrel
Ryan

They are torquing to 150 newton meters and a light coating of anti seize on the threads. Unless something has changed since I was there last. Very well could have.

And antisieze does not make threads come loose easier than dry.

 

[nm.otter]

Dry stainless threads rarely fare well.

 

[Sundodger]

Anti seize or other friction reduction is used on many joints to improve robustness against loosening. I have implemented many such over the years. Read my posts above about how friction reduces your confidence in the tq/ tension relationship.

Using threadlocker on a joint problem that Aaron describes with his action/bolt is at best a bandaid on a broken elbow. When in service forces meet or exceed residual tensile loads you have a ticking time bomb, and loctite will just add a bit more time to the clock. In the field it’s a general consensus that a joint that exceeds its clamp load in service is a failed joint, even if it hasn’t come apart yet.

 

[Sandstrom]

Dry stainless threads rarely fare well.

True, most connections that are tight and dry rarely go well!!