UM Tikka rings are not recommended for cartridges larger than 7mm PRC?

[Sundodger]

If you think other scope ring OEM’s are doing that you are naive at best. Won’t disagree in a perfect world this would be the way, but it is not happening in real life.

Haha, I shouldn't be so loose and fast throwing around the term "OEM". I was meaning OEM automotive, aerospace, defense, heavy equipment, etc. companies not little shops making their own gun parts, but that's a fair clarification and I can see how it was misunderstood.

 

[Sandstrom]

I'm still hoping for details on @Aaron Davidson 's observations of mount shifts on picatinny rails.

Yes please! Perhaps in a new thread…

 

[mxgsfmdpx]

Or you could go shoot and see what happens…

 

[Sandstrom]

Or you could go shoot and see what happens…

How is me shooting more going to show me details on someone else’s observations?

 

[mxgsfmdpx]

How is me shooting more going to show me details on someone else’s observations?

Go out and see what happens with UM tikka rings in a 7 PRC or greater. That’s what I did. Zero issues so far personally.

Just like some folks are told their scope will lose zero if you breathe on it wrong. How about go out and see for yourself

 

[mxgsfmdpx]

@Unknown Munitions ? Have you had ring failures with higher recoiling rounds?

7 PRC and 300 Win Mag have been zero issues for me so far.

 

[Sandstrom]

Go out and see what happens with UM tikka rings in a 7 PRC or greater. That’s what I did. Zero issues so far personally.

Just like some folks are told their scope will lose zero if you breathe on it wrong. How about go out and see for yourself

I agree with you on seeing for myself. I have had several scopes lose zero over the years, along with mounts that have moved or broke. I am not questioning my UM rings.

However I think you are missing my intent, which is why I suggested a new thread. A very well known and respected mogul in the firearms industry made a statement about the integrity of the most widely used mounting system on the planet (picatinny) He went as far to say that he wants to remove them from every rifle he owns. I am genuinely interested in his findings. Is there an actual problem or is it a hype/marketing move to sell a better version of the mouse trap?
There is no amount of shooting that I can do that will show me someone else’s findings and data.

 

[mxgsfmdpx]

I agree with you on seeing for myself. I have had several scopes lose zero over the years, along with mounts that have moved or broke. I am not questioning my UM rings.

However I think you are missing my intent, which is why I suggested a new thread. A very well known and respected mogul in the firearms industry made a statement about the integrity of the most widely used mounting system on the planet (picatinny) He went as far to say that he wants to remove them from every rifle he owns. I am genuinely interested in his findings. Is there an actual problem or is it a hype/marketing move to sell a better version of the mouse trap?
There is no amount of shooting that I can do that will show me someone else’s findings and data.

Yeah I get that sentiment for sure. I didn’t realize someone was against using pic rail and didn’t read the whole thread. I just read the thread title and the first comment regarding the UM rings and made my comment.

 

[mxgsfmdpx]

Ah I now see your post is directly above my reply, maybe thinking I was quoting you. My bad. No. My comment was about this thread not the pic rail stuff.

 

[Sandstrom]

Ah I now see your post is directly above my reply, maybe thinking I was quoting you. My bad. No. My comment was about this thread not the pic rail stuff.

No problem, I kind of thought that was what happened It threw me for a loop for a second

 

[SDHNTR]

7 PRC and 300 Win Mag have been zero issues for me so far.

What torque setting did you use on the base? UM recommended amount? Or more?

 

[mxgsfmdpx]

What torque setting did you use on the base? UM recommended amount? Or more?

Thread 'Do You Need Specs/Info On Setting Up Your Tikka/Maven RS1.2/UM Tikka Rings Combo? Look Here.'

Dec 15, 2024

I've gotten several PMs and texts over the last couple months as folks seasons are winding down and new rifles are on the horizon for off season training and then hunting next year.

I have put together 7 personal Tikka/Maven RS1.2/UM Tikka rings combos and have helped put together several others. Here are the torque specs I've landed on for continued success on the guns and scopes not losing their zero. Think practical field use and very nasty roads/off road trails minimum 3-5 days per week, combined with shooting hundreds of rounds per week.


Action Screws: With factory...

• mxgsfmdpx
• Replies: 34
• Forum: Firearms

• 

 

[Fowl Play]

TLDR: Started nerding out and typed out a monster below. Using properly spec’d shear pins to handle the recoil should be the easy answer. Bent pins means this was not done — I could easily see not multiplying by a Dynamic Amplification Factor as probable cause as I see professional engineers screw that up. Relying on friction is very problematic and should not be done if at all possible.


I should probably sit down and do the math on this at some point as it always interests me. Problem is, I don’t know what material fasteners are used, I could guess, but that’s vital information for the calcs.

In general it is bad practice to have a shear load held in friction especially a shock load like rifle recoil. (Yes most rail mounts do it, but it’s not best) What UM is trying to do is actually a hard problem to solve, and you really can’t make the torque value “dummy proof” if that’s what they are trying to do. Degreased vs greased threads, bases, rails, whether loctite is used. Thread spec tolerances, torque wrench calibration. All these things can compound to easily be +/-50% on how much torque is actually converted to preload in the joint. And is why you shouldn’t do it.

You can’t just specify a “torque value”. It absolutely has to be a process. UM could take a step in the right direction and define that process and that would be awesome to see. It should spec what degreaser to use, where and how to apply loctite, and torque. I’ve never seen a manufacturer do it (for rings or bases).

Design process for coming up with a torque value would look like this :

1. Take max scope weight with max recoil impulse. To get static F = ma load.
2. Critical part I see every single recoil calculator online fail at… you need to double this load as a “Dynamic Amplification Factor”. Theoretical maximum DAF is 2.0 — which rifle recoil would be approaching.
3. Determine frictional factor to use based on material combination in the joint.
4. Determine a “K factor” to use for what ever lubricant is chosen (probably loctite 243 )
5. Now here comes the hard part. To account for thread tolerances, torque wrench calibration, variances, etc you need to be able to handle at least +/- 25% preload uncertainty. That’s what amount of torque actually gets converted into preload. Spec’ing a torque value that will not plastically deform a bolt at the upper end, yet will still provide enough preload at the bottom end will be difficult.
6. Add in properly sized shear pins once you realize this math likely doesn’t close accounting for worst case frictional factors under all conditions. (Unless you start using exotic bolt materials).

The guys who aren’t having problems and haven’t used shear pins, likely have followed a rigorous prep/ install process, know how to use a torque wrench properly, and haven’t had tolerances and inherent variances stack up worst case against them.

 

[Sundodger]

TLDR: Started nerding out and typed out a monster below. Using properly spec’d shear pins to handle the recoil should be the easy answer. Bent pins means this was not done — I could easily see not multiplying by a Dynamic Amplification Factor as probable cause as I see professional engineers screw that up. Relying on friction is very problematic and should not be done if at all possible.


I should probably sit down and do the math on this at some point as it always interests me. Problem is, I don’t know what material fasteners are used, I could guess, but that’s vital information for the calcs.

In general it is bad practice to have a shear load held in friction especially a shock load like rifle recoil. (Yes most rail mounts do it, but it’s not best) What UM is trying to do is actually a hard problem to solve, and you really can’t make the torque value “dummy proof” if that’s what they are trying to do. Degreased vs greased threads, bases, rails, whether loctite is used. Thread spec tolerances, torque wrench calibration. All these things can compound to easily be +/-50% on how much torque is actually converted to preload in the joint. And is why you shouldn’t do it.

You can’t just specify a “torque value”. It absolutely has to be a process. UM could take a step in the right direction and define that process and that would be awesome to see. It should spec what degreaser to use, where and how to apply loctite, and torque. I’ve never seen a manufacturer do it (for rings or bases).

Design process for coming up with a torque value would look like this :

1. Take max scope weight with max recoil impulse. To get static F = ma load.
2. Critical part I see every single recoil calculator online fail at… you need to double this load as a “Dynamic Amplification Factor”. Theoretical maximum DAF is 2.0 — which rifle recoil would be approaching.
3. Determine frictional factor to use based on material combination in the joint.
4. Determine a “K factor” to use for what ever lubricant is chosen (probably loctite 243 )
5. Now here comes the hard part. To account for thread tolerances, torque wrench calibration, variances, etc you need to be able to handle at least +/- 25% preload uncertainty. That’s what amount of torque actually gets converted into preload. Spec’ing a torque value that will not plastically deform a bolt at the upper end, yet will still provide enough preload at the bottom end will be difficult.
6. Add in properly sized shear pins once you realize this math likely doesn’t close accounting for worst case frictional factors under all conditions. (Unless you start using exotic bolt materials).

The guys who aren’t having problems and haven’t used shear pins, likely have followed a rigorous prep/ install process, know how to use a torque wrench properly, and haven’t had tolerances and inherent variances stack up worst case against them.

You have your head in the right general direction; but there are some errors, missing steps, and such.

Reliance on the shear pin is poor form. Not saying to not use it, but if it's getting loaded at all in service, that means service loads have exceeded residual forces. When that happens screws can unthread, bolts/parts start accelerated fatigue, and down the spiral it all goes. Use the shear pin for "belt and suspenders" not as a primary.

Your force calculations are a little simplistic, prob fastest and cheapest to instrument up some edge cases with accelerometers and possibly strain gauges, then use FEA for initial designs.

On the right path for the compounding variables, but you get the probability calculations from your torque/tension tests on a statistically significant number of test coupons.

 

[Fowl Play]

You have your head in the right general direction; but there are some errors, missing steps, and such.

Reliance on the shear pin is poor form. Not saying to not use it, but if it's getting loaded at all in service, that means service loads have exceeded residual forces. When that happens screws can unthread, bolts/parts start accelerated fatigue, and down the spiral it all goes. Use the shear pin for "belt and suspenders" not as a primary.

Your force calculations are a little simplistic, prob fastest and cheapest to instrument up some edge cases with accelerometers and possibly strain gauges, then use FEA for initial designs.

On the right path for the compounding variables, but you get the probability calculations from your torque/tension tests on a statistically significant number of test coupons.

I have spent weeks in a lab doing torque/tension testing for my own spaceflight hardware. So know what’s involved. The method I described is exactly what is used in industry - slap on a factor of safety of 2 and you are golden. Lowering safety factor or +/- 25% uncertainty I stated requires allot of material friction and lubricant k-factor sample testing but unnecessary for something like this. This is solidly hand calc territory, via the method I describe, and shear pins are 100% the best method as primary load path for a shear load. Pin and slot, with loose tolerance holes around tension only fasteners is the primary loading condition for most secondary structure in critical applications.

Conversely relying on friction for a primary shear load is precisely how all the bad stuff you listed happens.

 

[mt terry d]

Dynamic Amplification Factor


aka fudge factor for us laymen?
Like " Refuse Logistics Specialist" for garbage man ?

 

[Sundodger]

I have spent weeks in a lab doing torque/tension testing for my own spaceflight hardware. So know what’s involved. The method I described is exactly what is used in industry - slap on a factor of safety of 2 and you are golden. Lowering safety factor or +/- 25% uncertainty I stated requires allot of material friction and lubricant k-factor sample testing but unnecessary for something like this. This is solidly hand calc territory, via the method I describe, and shear pins are 100% the best method as primary load path for a shear load. Pin and slot, with loose tolerance holes around tension only fasteners is the primary loading condition for most secondary structure in critical applications.

Conversely relying on friction for a primary shear load is precisely how all the bad stuff you listed happens.

Tell me you work at Boeing without telling me you work at Boeing.

Several weeks of experience sounds about right, your comments remind me of my overconfident junior engineers right out of college.

Relying on those shear pins? High cycle low stress fatigue has entered the chat...

 

[Fowl Play]

Dynamic Amplification Factor


aka fudge factor for us laymen?
Like " Refuse Logistics Specialist" for garbage man ?

Safety factor would be “fudge factor”. A DAF is a real variable you can calculate for if you have the right inputs. For an extremely stiff system (metal to metal contact) and near instantaneous load (recoil), it will be very close to 2.0 or twice what the calculated equivalent static load would be. The vibration and shock lab at my work is called “The house of pain” or “tower of terror” and quickly makes you a believer in the theory of it once you see it in person.

 

[Fowl Play]

Tell me you work at Boeing without telling me you work at Boeing.

Several weeks of experience sounds about right, your comments remind me of my overconfident junior engineers right out of college.

Relying on those shear pins? High cycle low stress fatigue has entered the chat...

Not going to go into credentials or experience, (I have plenty) but I disagree with you wholeheartedly at a very basic level. Even suggesting that FEA is required or is the best way to calculate preload in a joint is wrong.

Edit: I have gone back and read through many of your other comments on this thread and whole heartedly agree with the difficulties of a bolted joint design you mention. Threadforms, coating, frictional factors, etc all make determining preload consistently a nightmare. And it shows that you have done this before, probably at an intimate level. That is precisely why you use shear pins. Especially in a situation like this where you are not going to go through the process (money) to get test based material frictional factors or lubricant K factors, or specify some crazy high toleranced thread form, or take acceleration data from some crazy lightweight rifle with some new fangled hot cartridge, all the while trying to account for the vast majority of installs being done with sub par uncalibrated tools with untrained individuals. There is just too much variability in all of it. Especially when dealing with two very small fasteners per mount.

Still have the same problem with mounts to scope tube, but at least on the good mounts you have 4x fasteners per mount. Helps close the friction problem easier.

 

[Marbles]

This is getting amusing. I bet there are more than one functional way to skin this cat, as well as some very none functional ways.

A wheel hub is a shock loaded friction joint, and clearly works very well.

Lugs on a rifle bolt are clearly relying on one structure mechanically preventing the movement of another and works well.

The question is what works best in the context from a durability and function perspective? I'm willing to bet a combination of friction and pin.

Safety factors of two sound so low, but that is because I'm use to life safety uses where 10 is considered standard (not professionally, only from dabbling in rigging, overhead rescue, and tree work).