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Tuner Testing Part 2

Bryan Z.

Looks like the tuner can help to regain tune in high and low barometric pressure situations. The game plan is to continue testing in various atmospheric conditions such as high and low temperatures and high and low humidity to see if swings in temperature and humidity will show the same statistically significant repeatable results. I simply have not had the type of changes in temperature and humidity that I have had with barometric pressure thus far but anticipate that I will during the upcoming Spring and Summer.
 
jackieschmidt said:
Excellent.

You have got my attention with the barometric pressure. I have always tuned 130, 133, and 135 by humidity swings, mainly with the load.

What is the threads per inch of the tuner?

Good report.

By the way. Isn’t it amazing how one of these things will shoot when you hit the sweet spot.
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Yes, it’s always amazing when I find an effect that is statistically significant especially when it’s something like this where I’m really not sure why it’s happening BUT IT IS! And doing so in a very predictable pattern. This is why I look forward to seeing what temperature and humidity may do. With Spring around the corner and Summer looming, it will be great to keep the “regain tune” testing going and see what we get!
 
!Peter! said:
I wonder if using density altitude is a better parameter to track as it takes into account temperature, atmospheric pressure and humidity all in the one parameter?
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I think it's better to separate them out. We know why temperature and humidity change things. I've not heard a good explanation for why pressure would. So you need to be able to separate out the effects so that you don't wind up mistaking a change in humidity for a change in pressure, for example. You don't *need* to know why things are happening to shoot well. But progress is much faster (and often cheaper) if you do.
 
jackieschmidt said:
That small increment you moved the tuner only amounts to about .002 inch of linear motion.
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Looks like 40 marks on that tuner and 32tpi. So .00078 per mark. Less than a thou. It still amazes me how such tiny adjustments can make a difference. It's because we are shifting phase time, not frequency..per se. If it were frequency, it'd tak much larger increments to have the angular change that we see. But phase time is essentially just manipulating the where the anti-node(tor or bottom of sine) is when the bullet reaches the muzzle...of a single waveform.
 
gunsandgunsmithing said:
Looks like 40 marks on that tuner and 32tpi. So .00078 per mark. Less than a thou. It still amazes me how such tiny adjustments can make a difference. It's because we are shifting phase time, not frequency..per se. If it were frequency, it'd tak much larger increments to have the angular change that we see. But phase time is essentially just manipulating the where the anti-node(tor or bottom of sine) is when the bullet reaches the muzzle...of a single waveform.
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This is something that's been rattling around my brain for some time now. I think we've discussed it a bit.

I *think* I know what's going on here. This is all very back of the envelope, but it's food for thought.

If you check out the positive compensation article on the Border Barrels site, you can see some measurements of the muzzle motion.


The relevant motion seems to be be a sine wave that peaks about 3 times per millisecond. So roughly 3000 Hz. I know this is a very different rifle - a rimfire - but the frequency is still significant because the overall results should be roughly similar for centerfire in terms of the impact barrel motion has on the target.

Now check out Varmint Al's analysis of mode shapes.


Notice that the the 3000 hz mode is well down into the mode shapes. It's a pretty complex shape. This isn't super relevant, except that it shows you just how tiny and weird the vibrations can get. Keep in mind that all of these modes are superimposed on top of each other to varying degrees. The exact frequencies will move around quite a bit, but this shows we're in the same ballpark which is nice to know. Some frequencies will be excited more than others, based on the forces involved. It's also worth noting that Harold Vaughn's experiments also found that it was higher frequency modes that mattered.

The third thing to note is that resonant frequency of a barrel is proportional to 1/L^2, where L is the barrel length. So it's pretty sensitive to length.

But... What's bothering me is that small changes should not impact that frequency very much - maybe half a Hz or so per tick. It's a pretty small effect and not something that jibes with Kolbe's results very well - a couple of Hz wouldn't impact things very much. That said, these numbers do not account for the weight of a tuner, which definitely matters. So it's not totally out of the realm of possibility that it's just a frequency shift. Phase could also play a role, although I'm stumped as to how turning a tuner is going to change the phase. What's also missing is how much change is required to move a mode out of the range where it is excited by the firing impulse. My gut says that's going to require more than a Hz or two as well. There's still more to figure out here.

Now this is all very rough, and these numbers can vary widely, but I think it shows very generally how such small changes can have significant impact. Or at least, that it's not totally crazy. The data available pretty consistently shows that higher modes in in the low single digit kHz range are w hat matter.

It's just one piece of the puzzle, and I'm not sure there's any immediate practical benefit to it. But I think it's interesting.

EDIT: I rewrote some stuff on interpreting it to make it more clear.
 
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damoncali said:
This is something that's been rattling around my brain for some time now. I think we've discussed it a bit.

I *think* I know what's going on here. This is all very back of the envelope, but it's food for thought.

If you check out the positive compensation article on the Border Barrels site, you can see some measurements of the muzzle motion.


The relevant motion seems to be be a sine wave that peaks about 3 times per millisecond. So roughly 3000 Hz. I know this is a very different rifle - a rimfire - but the frequency is still significant because the overall results should be roughly similar for centerfire in terms of the impact barrel motion has on the target.

Now check out Varmint Al's analysis of mode shapes.


Notice that the the 3000 hz mode is well down into the mode shapes. It's a pretty complex shape. This isn't super relevant, except that it shows you just how tiny and weird the vibrations can get. Keep in mind that all of these modes are superimposed on top of each other to varying degrees. The exact frequencies will move around quite a bit, but this shows we're in the same ballpark which is nice to know. Some frequencies will be excited more than others, based on the forces involved. It's also worth noting that Harold Vaughn's experiments also found that it was higher frequency modes that mattered.

The third thing to note is that resonant frequency of a barrel is proportional to 1/L^2, where L is the barrel length. So it's pretty sensitive to length.

What's bothering me is that small changes should not impact that frequency very much - maybe half a Hz or so. It's a pretty small effect. None of this back of the envelope stuff is enough to quantify it. But it's not unreasonable to think it could just be a frequency change. Or maybe by shifting the frequency, it pushes it closer to the driving frequency and therefore changes the amplitude of that mode.

Now this is all very rough, and these numbers can vary widely, but I think it shows very generally how such small changes can have significant impact. The data available pretty consistently shows that higher modes in in the low single digit kHz range are what matter.

It's just one piece of the puzzle, and I'm not sure there's any immediate practical benefit to it. But I think it's interesting.
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One of the most interesting things(to me) that has come from vibration analysis was shooting the same rifle glued and screwed vs just screwed. No other changes and the bbl vibrated at a different frequency and was 2 marks(.002) out of tune but at a completely different node due to it being a totally different frequency. Point being, this proved movement at a perfectly bedded point between stock and action at high enough frequencies, yet still only 2 marks away..well within the range of a single wave form and shooting the same as glued. I thought that was extremely interesting and telling. Phase time.

It's this inevitable high freq movement that is the reason that I do not subscribe to clamping or collet attachment as being better or worse than not. I promise, it still moves. I believe every joint in the system moves...that teeny, tiny high freq bit.
 
gunsandgunsmithing said:
One of the most interesting things(to me) that has come from vibration analysis was shooting the same rifle glued and screwed vs just screwed. No other changes and the bbl vibrated at a different frequency and was 2 marks(.002) out of tune but at a completely different node due to it being a totally different frequency. Point being, this proved movement at a perfectly bedded point between stock and action at high enough frequencies, yet still only 2 marks away..well within the range of a single wave form and shooting the same as glued. I thought that was extremely interesting and telling. Phase time.

It's this inevitable high freq movement that is the reason that I do not subscribe to clamping or collet attachment as being better or worse than not. I promise, it still moves. I believe every joint in the system moves...that teeny, tiny high freq bit.
Click to expand...
I would expect changes in bedding to change frequency. How a structure is constrained can have a big impact. Think about how frequency would change on a cantilever beam if you supported it at both ends rather that one - its a HUGE change. So it seems reasonable that adding glue would result in a small change. I don't think that proves that it's a phase change, but it is interesting.

I don't want to derail the thread too much - I think the topic is more about tuning and air pressure, but there's clearly a lot we don't understand about what's going on here.
 
damoncali said:
I would expect changes in bedding to change frequency. How a structure is constrained can have a big impact. Think about how frequency would change on a cantilever beam if you supported it at both ends rather that one - its a HUGE change. So it seems reasonable that adding glue would result in a small change. I don't think that proves that it's a phase change, but it is interesting.

I don't want to derail the thread too much - I think the topic is more about tuning and air pressure, but there's clearly a lot we don't understand about what's going on here.
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Just trying to help you out. Look at the various sine wave tests by me and others. The test physically shows a full nodal cycle, done properly and top to middle(anti-node to node) is only 4-5 marks(thousandths) on my tuner and double that from top to bottom anti-nodes. I've never seen any mathematical formula/model where moving the tuner by that small amount can account for the full cycle that happens...not even close. So even if you don't believe it's phase time, disproving freq change as the cause/affect is the easy part. No, I don't have those calculations handy but I've spoken about this with multiple engineers who all agree with this.
 
damoncali said:
I would expect changes in bedding to change frequency. How a structure is constrained can have a big impact. Think about how frequency would change on a cantilever beam if you supported it at both ends rather that one - its a HUGE change. So it seems reasonable that adding glue would result in a small change. I don't think that proves that it's a phase change, but it is interesting.

I don't want to derail the thread too much - I think the topic is more about tuning and air pressure, but there's clearly a lot we don't understand about what's going on here.
Click to expand...
Your last sentence says a lot.

I do a lot of things based solely on the fact that they work. How do I know they work? The Rifle performs at a competitive level.

All of our theory’s work fine as long as all variables are taken into account.

But just think of all of the stacked variables that occur from the instant the trigger is released until the time the bullet hits the target.
 
jackieschmidt said:
Your last sentence says a lot.

I do a lot of things based solely on the fact that they work. How do I know they work? The Rifle performs at a competitive level.

All of our theory’s work fine as long as all variables are taken into account.

But just think of all of the stacked variables that occur from the instant the trigger is released until the time the bullet hits the target.
Click to expand...
Absolutely. For me, part of the fun is teasing apart they whys and applying that knowledge. But at the end of the day, you can't think your way to small groups. We just have to do what works and get comfortable with our ignorance. I still don't know why seating depth matters. I think these tests have added atmospherics onto my pile of mysteries to solve.
 
gunsandgunsmithing said:
Just trying to help you out. Look at the various sine wave tests by me and others. The test physically shows a full nodal cycle, done properly and top to middle(anti-node to node) is only 4-5 marks(thousandths) on my tuner and double that from top to bottom anti-nodes. I've never seen any mathematical formula/model where moving the tuner by that small amount can account for the full cycle that happens...not even close. So even if you don't believe it's phase time, disproving freq change as the cause/affect is the easy part. No, I don't have those calculations handy but I've spoken about this with multiple engineers who all agree with this.
Click to expand...
I'm not saying I don't believe it. I'm saying I can't explain it. Just trying to chip away at the whys.
 
damoncali said:
Absolutely. For me, part of the fun is teasing apart they whys and applying that knowledge. But at the end of the day, you can't think your way to small groups. We just have to do what works and get comfortable with our ignorance. I still don't know why seating depth matters. I think these tests have added atmospherics onto my pile of mysteries to solve.
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Glad I can add to the mysteries . I really wish I could have accurate explanations for a lot of the effects and non-effects I find with my testing and I probably could pull it off if I had the means to do so. If you know what the next Powerball numbers are going to be, please let me know and I’m sure the winnings would go a long way in finding explanations . For now, I’ll stick to the practical side of testing and what I’ve learned so far. Without any other further test data and combining my testing with Bryan Litz’s testing, my current practical conclusions and associated guidelines are:
1. The rifle has to have a well-tuned initial load developed. In my case, developing the load with the tuner on and screwed all the way on. This could be a key step in the process that delineate my results from Litz’s because his rifles were not well-tuned prior to turning the tuner.
2. Record all available atmospherics during all shooting with the tuner. This will enable an analysis of the impact of those variables on tune.
3. Shoot the sine wave test and examine closely the group shapes, sizes, and POI.
4. Set the tuner in the middle of a great “tune window” where group shape, size, and POI are very similar and would be considered a good competitive tune.
5. Turn the tuner when atmospherics indicate based on the atmospheric and group data that you have tracked. Examine whether the tune window has possibly shifted in accordance to variations in atmospherics.
As of right now, this seems to be one effective practical method to use the tuner to regain tune. The method is especially useful when preloading for matches where you cannot change your ammo characteristics (e.g., powder charge, seating). As I continue to test more with various different types of tuners in various atmospheric conditions with different barrel contours and chamberings, the guidelines may change but thus far, this is what the data is telling me.
 
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