Bill Norris
Back in the Day
NOTES - ADJUSTING TUNERS - MORE THAN JUST SHOOTING GROUPS AND TURNING IT
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Not sure if these facts will help or confuse tuner users but thought I would post this as I have read articles and watched videos since I began using tuners about 3 years ago. I find it interesting and thought I would share.
The number one point to keep in mind about all of these findings by whom ever - NOTHING is chiseled in stone. Meaning there are points made here that are opinions and findings of shooters just like us and some findings do duplicate. This is simply info that may be found helpful or may be expelled completely by other findings.
BACK GROUND (Down and Out and Vertical - IN Horizontal - OUT) - Theory says if Temp. goes down turn the tuner outward (away from the muzzle) and reverse if Temp. goes up. Barometric pressure, air density, and relative humidity "can" cause this theory to present frustrations in certain atmospheric conditions. Also, there is the consensus by some that if groups present Vertical - turn the tuner IN and if groups present Horizontal - turn the tuner OUT with adjustments.
Temps are thought by some shooters to be the major determining factor of how and why the tuner works. Huge mis-conception. Other variables are at play. On some trips to the range one may follow temp. alone for tuning but in some examples, due to atmospheric air pressure changes, (density altitude) the rifle may or may not stay in tune over the same temp. range OR pressure changes on a different day. On top of that, different powders and even different loads respond differently to atmospheric changes. Therefore, tuning is an on-going process most of the time when changing locations or even when weather changes at the same location. There is no set and forget with tuners. However, once the load is tuned for a certain condition and location it is recommended to not turn the tuner unless the groups open up.
VERY IMPORTANT
===============
Density Altitude is basically a composite number that factors in physical altitude above sea level, temperature, relative humidity, barometric pressure, etc. and creates a conditional number known to be helpful as a reference for tuning powder charges and serves as a guide for adjusting the tuner as well.
A tool for measuring the above number is sold by Kestrel - Drop D-3 Wireless Temperature, Humidity and Pressure Data Logger - $129.00 @ Amazon
Needless to say there is a lot more to be learned about these changes and how
much it affects FIRST the powder burn rate and secondly rifle harmonics.
SOME FINDINGS OF A TUNER BUILDER AND USER
=================================
Tim Sellars advocates that the function of the tuner ONLY affects the vertical distortion of barrel vibrational harmonics and re-aligns that vertical distortion with the bullet exit timing during "barrel whip" which in theory should cause group size to be smaller. Other aspects of the complete rifle such as the weight of that portion of the rifle above and below the center of the bore, barrel length, and points of contact with the action will affect the barrel whip. Very important to keep everything the same once the load development begins. Test have shown small and minor changes such as the way the shooter holds and grips the stock can and will sometimes make a huge difference in the tuning as a whole.
There is a demanding objective here. "The rifle/load must be at maximum accuracy from load development prior to the tuner adjustment" meaning the powder, powder charge, primer, seating depth, etc. is at a point of working together. The tuner will not correct a load that is not at peak accuracy and/or bullet wobble. The tuner has zero to do with the load. No free lunch. Make sure you have milked every ounce of accuracy from the rifle/load combination available prior to attempting to tune.
One other very important note from Tim's experiences is the importance of the separation between what the tuner controls vs. what seating depth controls. It was long believed these two worked hand in hand at controlling barrel vibrations but conversely Tim says the tuner controls vertical dispersion caused by harmonics and seating depth controls ramdom muzzle dispersion which is created by "bullet wobble" when entering the barrel at time of firing. In other words the tuner adjust vertical movement and seating depth adjust horizontal movement at the point of impact and on the target. However, another school of thought by many shooters says by turning the tuner inward towards the shooter will decrease vertical dispersion and turning the tuner away from the shooter will decrease horizontal dispersion.
While on the subject of vibrations Tim has also indicated from his testing and findings there is a secondary high frequency vibration at the time of ignition that is created simply by the forces of the case body slamming against the chamber walls and the bolt lugs locking up. It travels along the barrel ahead of the harmonic vibrations and it will alter tuning. His theory indicates since there is only one spot in the complete powder charge testing that is affected by this high frequency vibration that increasing or decreasing the powder charge by 1/2 grain will move the tune away from this high frequency vibration and remove the affects of it on group size and tuner settings. He also goes on to say that the bullet can pick up this high frequency vibration and actually carry it along and produce instability. Evidence of this condition being present is seen while adjusting the tuner and actually not seeing any or much changes at all to the group size.
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POSITIVE COMPENSATION - WHEN A SLOWER BULLET IS AIMED BY THE BARREL TO A HIGHER POI ON THE TARGET
==========================================================================
Here is where the tuner affects gets somewhat muddy or complicated for some and cause arguements. Lots of controversy exist around this. Many test have been conducted by shooters and ballisticians to try and prove or disprove the theory. The fact remains that this does happen if each shot is marked or recorded on the target and M V is assigned to each individual shot fired. The idea is fairly simple in that the barrel will be in an elevated position of the "whip" when the slower bullet is released from the muzzle and the barrel will be at a lower position in the "whip" when the faster bullet is released therefore causing the two to actually cross paths at some given point down range. This is called convergence. Tim goes on to say that moving the tuner inward towards the shooter will speed up the "whip" and moving it outward away from the shooter will slow the "whip" down. In theory this makes perfect sense if one considers the weight of the tuner in regards to the position of the tuner.
Going back to load development for a second and not considering the tuner, Tim also states that by running a graph with several different powder charges of one whole grain apart at the beginning of load development will demonstrate these results clearly at longer distances. He says the tune window of the load will show the higher powder charges impacting at a lower POI on the target with this testing. Once the POI shifts from that pattern and reverses then that powder charge would indicate the load tune is no longer good BUT, the rifle may shoot acceptable with either of the powder charges prior to the shift in POI. This of course would be done with the tuner set at zero. I have not been this deep into load development at longer distances but find it interesting.
==========================================================
Not sure if these facts will help or confuse tuner users but thought I would post this as I have read articles and watched videos since I began using tuners about 3 years ago. I find it interesting and thought I would share.
The number one point to keep in mind about all of these findings by whom ever - NOTHING is chiseled in stone. Meaning there are points made here that are opinions and findings of shooters just like us and some findings do duplicate. This is simply info that may be found helpful or may be expelled completely by other findings.
BACK GROUND (Down and Out and Vertical - IN Horizontal - OUT) - Theory says if Temp. goes down turn the tuner outward (away from the muzzle) and reverse if Temp. goes up. Barometric pressure, air density, and relative humidity "can" cause this theory to present frustrations in certain atmospheric conditions. Also, there is the consensus by some that if groups present Vertical - turn the tuner IN and if groups present Horizontal - turn the tuner OUT with adjustments.
Temps are thought by some shooters to be the major determining factor of how and why the tuner works. Huge mis-conception. Other variables are at play. On some trips to the range one may follow temp. alone for tuning but in some examples, due to atmospheric air pressure changes, (density altitude) the rifle may or may not stay in tune over the same temp. range OR pressure changes on a different day. On top of that, different powders and even different loads respond differently to atmospheric changes. Therefore, tuning is an on-going process most of the time when changing locations or even when weather changes at the same location. There is no set and forget with tuners. However, once the load is tuned for a certain condition and location it is recommended to not turn the tuner unless the groups open up.
VERY IMPORTANT
===============
Density Altitude is basically a composite number that factors in physical altitude above sea level, temperature, relative humidity, barometric pressure, etc. and creates a conditional number known to be helpful as a reference for tuning powder charges and serves as a guide for adjusting the tuner as well.
A tool for measuring the above number is sold by Kestrel - Drop D-3 Wireless Temperature, Humidity and Pressure Data Logger - $129.00 @ Amazon
Needless to say there is a lot more to be learned about these changes and how
much it affects FIRST the powder burn rate and secondly rifle harmonics.
SOME FINDINGS OF A TUNER BUILDER AND USER
=================================
Tim Sellars advocates that the function of the tuner ONLY affects the vertical distortion of barrel vibrational harmonics and re-aligns that vertical distortion with the bullet exit timing during "barrel whip" which in theory should cause group size to be smaller. Other aspects of the complete rifle such as the weight of that portion of the rifle above and below the center of the bore, barrel length, and points of contact with the action will affect the barrel whip. Very important to keep everything the same once the load development begins. Test have shown small and minor changes such as the way the shooter holds and grips the stock can and will sometimes make a huge difference in the tuning as a whole.
There is a demanding objective here. "The rifle/load must be at maximum accuracy from load development prior to the tuner adjustment" meaning the powder, powder charge, primer, seating depth, etc. is at a point of working together. The tuner will not correct a load that is not at peak accuracy and/or bullet wobble. The tuner has zero to do with the load. No free lunch. Make sure you have milked every ounce of accuracy from the rifle/load combination available prior to attempting to tune.
One other very important note from Tim's experiences is the importance of the separation between what the tuner controls vs. what seating depth controls. It was long believed these two worked hand in hand at controlling barrel vibrations but conversely Tim says the tuner controls vertical dispersion caused by harmonics and seating depth controls ramdom muzzle dispersion which is created by "bullet wobble" when entering the barrel at time of firing. In other words the tuner adjust vertical movement and seating depth adjust horizontal movement at the point of impact and on the target. However, another school of thought by many shooters says by turning the tuner inward towards the shooter will decrease vertical dispersion and turning the tuner away from the shooter will decrease horizontal dispersion.
While on the subject of vibrations Tim has also indicated from his testing and findings there is a secondary high frequency vibration at the time of ignition that is created simply by the forces of the case body slamming against the chamber walls and the bolt lugs locking up. It travels along the barrel ahead of the harmonic vibrations and it will alter tuning. His theory indicates since there is only one spot in the complete powder charge testing that is affected by this high frequency vibration that increasing or decreasing the powder charge by 1/2 grain will move the tune away from this high frequency vibration and remove the affects of it on group size and tuner settings. He also goes on to say that the bullet can pick up this high frequency vibration and actually carry it along and produce instability. Evidence of this condition being present is seen while adjusting the tuner and actually not seeing any or much changes at all to the group size.
==========================================================================
POSITIVE COMPENSATION - WHEN A SLOWER BULLET IS AIMED BY THE BARREL TO A HIGHER POI ON THE TARGET
==========================================================================
Here is where the tuner affects gets somewhat muddy or complicated for some and cause arguements. Lots of controversy exist around this. Many test have been conducted by shooters and ballisticians to try and prove or disprove the theory. The fact remains that this does happen if each shot is marked or recorded on the target and M V is assigned to each individual shot fired. The idea is fairly simple in that the barrel will be in an elevated position of the "whip" when the slower bullet is released from the muzzle and the barrel will be at a lower position in the "whip" when the faster bullet is released therefore causing the two to actually cross paths at some given point down range. This is called convergence. Tim goes on to say that moving the tuner inward towards the shooter will speed up the "whip" and moving it outward away from the shooter will slow the "whip" down. In theory this makes perfect sense if one considers the weight of the tuner in regards to the position of the tuner.
Going back to load development for a second and not considering the tuner, Tim also states that by running a graph with several different powder charges of one whole grain apart at the beginning of load development will demonstrate these results clearly at longer distances. He says the tune window of the load will show the higher powder charges impacting at a lower POI on the target with this testing. Once the POI shifts from that pattern and reverses then that powder charge would indicate the load tune is no longer good BUT, the rifle may shoot acceptable with either of the powder charges prior to the shift in POI. This of course would be done with the tuner set at zero. I have not been this deep into load development at longer distances but find it interesting.
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However, it might be difficult to obtain it in sufficient quantity. 
