More on Barrel Tuners

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Barry Davies
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Re: More on Barrel Tuners

#106 Postby Barry Davies » Tue May 29, 2018 10:57 am

Might as well join the fun.
! A point on a standing ( sine ) wave where amplitude is minimum.
2 Yes
3 4
4 No
5 Maybe but would not bet on it.
7 CW
8 Yes
9 Fouling or significant atmospheric change.
10 Clean or retune.
11 Absolutely no idea.
12 Normal vibration pattern
13 Short --3, Mid -- 5, Long -- 1.
14 1.

GSells
Posts: 335
Joined: Sun Aug 13, 2017 11:04 pm

Re: More on Barrel Tuners

#107 Postby GSells » Tue May 29, 2018 7:31 pm

1.A node is a point along a standing wave where the wave has minimum amplitude. For instance, in a vibrating guitar string, the ends of the string are nodes. ... The opposite of a node is an anti-node, a point where the amplitude of the standing wave is a maximum. These occur midway between the nodes. Thanks wiki !
2 yes
3. 4.
4. No I wouldn't use it !
5. No not likely, maybe if u had no conditions, it would be hard work.
7.Still I say right .
8.if was a naked barrel , then Yes . The harmonics were altered , greatly!
9 load slowing down and the projectile chasing the obt, the vibrations are beating the pill to the muzzle.

10..speed up the load and re seat depth tune and ocw tune .Or adjust tuner .
11. Round robin tuning , to keep the heat under control as not to induce false harmonics .
12.the tune is following the sine wave .
13. Groups 1 short , 5 mid , 5 longs.
14. Group 5 .
Ok Master , how did I go this time ? [-o<

williada
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Joined: Wed Jul 22, 2009 12:37 am

Re: More on Barrel Tuners

#108 Postby williada » Tue May 29, 2018 9:33 pm

Lot of squirrels out there boys. Least you blokes have put your nuts on the line. The most important part of a team is willingness. No free lunches unless you put in.

williada
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Joined: Wed Jul 22, 2009 12:37 am

Re: More on Barrel Tuners

#109 Postby williada » Wed May 30, 2018 9:03 pm

In the diagram above, a variable tuner was applied and moved in increments which amounted to one turn in total. The difference the tuner moved along the barrel for each group represented approximated 1.6 thousands of an inch for a total of 8 thousands of an inch in one turn. It demonstrates you are never far away from a tune on an anti-node (physics speak). Shooters see these spots as nodes through common usage of the term which may stem from other disciplines in language, engineering, geometry, computer science, horticulture and medicine. Shooters use terms like upper nodes and recognize they are velocity dependent etc but in physics they are identified as anti-nodes in forward or backward positions. So the confusion is not a lack of concept but one of communication. People are not wrong as such for using different terminology. A cockel in one state is a pipi in another. We all derive meaning from experience and convention. But to turn to the subtleties of what's happening, and then physics is more appropriate because physics is a science that studies matter, energy, motion and force and so offers greater understanding of more complex interactions.

If we use physics speak for node definition, not shooter speak, then the classic physics nodes in this example above are halfway between the phases of greatest amplitude between the crest and the trough. They happen to be bigger groups. Perhaps if the barrel was stiffer they may be smaller. The nodes in physics speak lie along an axis in this example (orange line). The peaks and troughs represent a slice or section along a three dimensional object rotating around the axis at a point in time. We see the long two dimensional section as a sine wave. If higher order waves (not high frequency low order waves) are not distorted, then the nodes always lie halfway between the anti-nodes. This is important, because the sine wave pattern will be rhythmic indicating reduced interference from other sources or tensions such as reflection of unwanted frequencies, torque or setup, take down screws or scope tension etc. This indicates a barrel in pretty good shape and the gear has real potential otherwise you have to chook around to eliminate problems.

The other thing to know in very simple terms is that the sine wave (standing wave) is not a wave but a pattern where say an incident wave (mechanical cause) traveling one way is met by a reflected wave travelling in the opposite direction at the same frequency (size). The interference wave generated which we plot as a sine wave has two parts of great interest to shooters - The node and the anti-node. The node (physics) appears as a point of minimum amplitude about an axis or the centre of the wave height when the two waves through their timing appear to overlap to look like one balanced wave rather than look like overlaps of two separate traced waves going in different directions. This is because one wave slides through the other and the toughs and peaks of both waves destruct one another to reduce amplitude at this point. On the other hand the energy at the crests or troughs is reflected from a boundary of the medium. The difference between the peaks and troughs is not the maximum amplitude of the interference wave because that is measured from the centre of the wave in physics speak. Shooters will see the swing from crest to trough as height of the wave. The energy of the two waves travelling towards the boundary of the medium doesn't destruct but rather is a constructive force to build build amplitude before they are reflected from the boundary. We work on little differences on wave angles at the boundaries when the sync of the two travelling waves going in different directions is not in sync with a tuner. If the sync is not perfect the node will form bigger groups too. This means both the node and the anti-node are interference patterns. Where we see lots of nodes in our sine wave it is a clue they are subdivisions of the fundamental frequency which has not completed at the muzzle either in its first cycle or part of another one so we have to tap into lower order frequencies but higher frequencies (different terms) of shorter wavelength for tune. All frequencies are equal divisions of the fundamental frequency.

The latter is important because a tuner changes suitable frequencies that form waves. The frequency of a wave is determined by its velocity through a medium such as a barrel. In this case they are closed one end harmonic patterns produced from the bolt face. The lowest frequency is determined by the amount of energy at which the medium will vibrate. We see that in a flexible barrel producing a longer wave length. The speed at which frequencies travel through the barrel depends on its composition, hardness, tension (stiffness), and thickness. The wave length of a harmonic also depends on the length of the barrel and its harmonic number i.e. 1 for lowest frequency. A tuner with a bloop tube of varying length may be used to find the most suitable frequency or harmonic length for group size. If we add a thimble to the bloop tube we can further control where a crest or trough bunches at the boundary i.e. the reflected frequencies for the best exit point for the bullet so as not to distort the muzzle. This is because variation in the properties of the medium by way of the tuner thimble or rings the bloop tube diameter or rubber covering, combine with length to result in variations of frequency that vibrate the barrel. In real life, with heavy F class barrels, the lowest frequency (1st Harmonic or higher order frequency) of giving the most muzzle lift is partly formed at bullet exit, so we tend to tune on higher frequency vibrations of lower order. This why stiffer barrels produce choppy groups because the harmonics represent higher frequencies with shorter wave lengths. In reality, we have to realize highest order frequencies are partly present to give macro muzzle lift. That may be 1st, 2nd or 3rd harmonic etc. I think Varmint Al found 9 from distant memory. Also given the the main sources of inertia for vibration are vastly different (chamber, throat, torque and muzzle), there is a very complex interaction of travelling waves and therefore timing to optimize the system. The muzzle exit where there is chatter from very high frequency is very important in a micro tune for muzzle shape and direction which is separate from the macro lift generated by lower frequencies. After all the muzzle shape and the angle where it is pointing determines the path the bullet follows in the first instance. A major shock wave comes from the ignition of powder to form gas before the bullet even moves and supplementary shock waves occur as the projectile engages the throat for swaging, then the rifling with further displacement and twisting forces of torque and finally with the change in friction as the bullet body reduces engagement when it pops the muzzle.

A pet load was used for the initial tuner tests above in Ecomeat's plot with known characteristics based on a data driven approach. Assume the velocity SD was about 6 fps and representative of a bigger data set. So the velocity between groups was relatively constant in practical terms as was the case with Ecomeat’s test. Perfect harmonic tunes are strictly velocity dependent. In real life there is always a a small variance due to barrel heat and fouling which changes harmonic lengths (up to .005"). Our goal is to optimise things. This is one reason why it is important to get your ignition and load developed prior to testing with a tuner as well as to use 140 yards as a test distance to see where your shots really go in the lay of a pattern. You can't distinguish where individual shots fall to determine a true group axis (as opposed to the axis running through the nodes) at closer distances when fired as a group because coning effects may mask dispersion as does mirage, wind and spin drift at longer distance. Furthermore, previous posts of testing at 140 yards by Ecomeat correlated with group shape at distances from 300 yards to 1000 yards. The groups merely breathed in and out as positive compensation varied. This is where other models are a tad flawed is because there is the assumption fast velocity shots go higher than slow velocity shots - this not always the case. This means that SD's are AT best a guide in the real world although they are data driven. They might be precise in method but the method does not always match the application.

Data driven enthusiasts may find it is acceptable to use 3 shot groups in the test scenario at 140 yards because the groups had the same charge and seating depth and velocity of the larger, significant data set with the same barrel. (If you do not have a large data set then ES is the next most reliable measure and usually represents the boundaries of reflection over a series of three shot groups with a pet load and gives you an idea of where the barrel weaknesses or strengths lie). All of Ecomeat’s groups including the rough nodes could achieve a possible but you would have to be on your toes with wind reading, particularly with the lateral groups. I do not accept “Oh it was great lateral, my load is great but I failed to read the wind" when a hummer group merely required a tweak of the tuner. Or chasing elevation in a hollow nodal group when the velocity was stable. It is another issue if velocity was significantly different and that scenario requires greater movement of the tuner. I prefer to use ES as a measure because I do not want to wear a new barrel out. Overtime you recognize what works and there is no point to endless testing. I use that in conjunction with a polynomial ladder test which I have also posted before to determine a preliminary test charge to reduce velocity spread for the initial test of tuner position which I must just set and forget like a barrel without a tuner.

There are some very significant observations from Ecomeat's groups with the tuner attached at 140 yards. Firstly, for the data enthusiasts, the worst groups appear on the node (physics speak) despite a low SD. The anti-nodes (physics speak) in an harmonic tune form the best groups. The anti-nodes reflections are more easily controlled by the leverage of the tuner and by its ability to change the medium and therefore change frequency of the vibrations which changes the angle of their reflection. The tuner assists to bunch high frequencies which otherwise may distort important low frequencies by their many and cumulative effects when they are out of sync. Or bunching may complement low frequencies presenting a more rhythmic in sync application. If frequencies are rhythmic they represent an harmonic length. We know that forms a standing wave when waves meet travelling from different directions to enable us to tap into a suitable tune. These are tiny frequencies in a high powered rifle that matter at the muzzle and may equate to harmonic numbers anywhere between 19 to 25 depending on your gear's personality in a heavy barrel and therefore interaction of sub frequencies which may, in a poor setup, distort the fundamental frequency which is partially complete in the feedback and at the muzzle.

Secondly, those hollow groups at the nodes in the diagram above do not need a clean, but rather a small movement of the tuner given the average velocity had not been changed by conditions or venue and the string was shot in one session.

(If the velocity had changed significantly by way of air density for example, then advanced users would vary the muzzle angle a tad more with the tuner and then sneak up on a suitable anti-node. Separate tuner tests are required at varying charges to accurately determine tuner movements to match velocity changes. In this case you go to genuine upper or lower anti-nodes established at different velocities in your horizontal charge test (ladder test) and work the tuner around those anti-nodes to pre-determine settings. Or you could pre-empt velocity changes by doing further homework to establish temperature velocity correlations to estimate where your tune should be. A tune is never far away but its shape usually varies).

A rhythmic pattern assists to estimate tuner thimble position. Nodes are halfway between anti-nodes. Such a tuner is ideally custom made to match the barrel’s personality which is another topic.

Finally, given the distance between an acceptable tune is not far apart if you look at troughs or crests in the plot above. Do not confuse these with shooter speak of the upper and lower node which really refers to a strict velocity change producing tight groups at anti- nodes forward or backward along the plot. Note well the diagram above does not refer to velocity changes. They are relatively constant. However as already indicated an advanced tuner user may substitute for this by moving the tuner large amounts which may change the muzzle exit angle or they may previously tested powder charge and looked for tuner correlations. But remember, the groups will change shape until a cycle on a desired frequency has completed and that shape makes them more or less conducive to compensation or different wind vectors. Bear in mind, at extreme range, the group tends to form an ellipse unless velocity is maintained at an acceptable average. That means nice round groups at short range may change shape. If you play the percentages, then the small anti-node movements and set and forget are great. I prefer to use upper velocity windows if they are suitable to penetrate turbulent air and sacrifice maybe tighter groups found in stable conditions at lower velocities particularly at long range. If velocity changes due to conditions selecting a minor compensation ant-node with that tad of vertical and least wind sensitive characteristic can be a good option. Remember a positive compensation point occurs before a peak and after a trough. So a whisker on the tuner is all you need. You have to know whether to come back or forward to the appropriate anti-node. If a big velocity change is encountered and you do not have access to reloading gear on the spot to beef or reduce your load to get the prescribed velocity then generally if you are getting elevation move the tuner out. If you want to reduce lateral move the tuner in. Beware a poor chamber or wrong seating depth can cause in bore yaw and your causal diagnosis has to be right, just like light changes or mirage are not tune problems.

We know a nice round group forms when muzzle oscillation from lateral to vertical is in a 1:1 ratio. In tuner terms, the group forms closer to the node axis where there is minimum amplitude. Can you pick it in the diagram above? Sometimes such groups do have a frequency distortion which we can use to our advantage. It may be least wind sensitive and just a tad further from the node axis than a round group would be. Can you pick it? Both groups are reliable. The further a group is away from the nodal axis then that muzzle oscillation may move to 1:2 or vice versa. It is still a respectable anti-node (physics speak), but the axis of the anti node in this case will determine the group suitability for compensation, long range ellipses and wind sensitivity or wind vector (to counter aerodynamic jump particularly at shorter distances). Can you identify which goes with what? OCW tunes are best performed when the barrel is in its straightest position and obviously close to the node axis. They require tight velocity spreads to maintain group size. If they are not rounder groups they are not OCW tunes and may indicate strain or tension in the system. So in OCW scenario it is true you can technically fall off the node or its axis. Conversely, the harmonic tune is really a tune on the anti-node. So you can technically fall off the anti-node on a peak or crest down the slope towards the trough. Harmonic tunes are strictly velocity dependent.

A long node (shooter speak) is not really a node for three reasons. One being it is an anti-node (physics), and the other being an element of positive compensation may occur before the true anti-node such that slower shots are tossed higher than faster ones and intersect at a specific distance on one hand or after a trough anti-node when the barrel rises again and blend with the peak or trough. Positive compensation always occurs on a rising muzzle angle. If the rise is tiny the trajectory is flatter, and the compensation point is closer. Or thirdly, on a straight barrel in neutral rise position is very close to or on a node with minimum amplitude where strict SD of velocity applies to the point of weighing primers. The latter is categorized by many shooters as a non harmonic tune. A strict compensation tune is not a harmonic tune either because acceptable velocity spreads occur in a window with higher ES.
Last edited by williada on Tue Jun 05, 2018 10:27 am, edited 2 times in total.

Gyro
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Location: New Zealand

Re: More on Barrel Tuners

#110 Postby Gyro » Thu May 31, 2018 6:08 pm

Considering this is all happening in less than the blink of an eye then do u have the maths/science for how the various velocity spread numbers impact on the direction the barrel is pointing right at the bullets exit moment ? I would presume a bloody small velocity change ( and by implication seating depth ? ) could screw with the veracity of any 'barrel time' tests ? And r u running a chrony WITH the above tests to help with the analysis of all shots ?

The ES question has been a real stumbling block to my acceptance of this stuff, or at least as I UNDERSTAND IT i.e. if proper tests that factor in the velocity PER SHOT do fit with the theory then I'm a great deal more interested. My own experience with muzzle velocity variations reveals just how easily it changes, even with the gun handling.

sungazer
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Joined: Fri Mar 17, 2017 7:58 pm

Re: More on Barrel Tuners

#111 Postby sungazer » Thu May 31, 2018 6:37 pm

My question is more along the lines of what causes the fundamental, and how is that faster at traveling down the barrel than the projectile. The first step would be to determine what is the cause of the fundamental, what is its frequency? then we know the time it takes to travel, we can then also have an idea of the harmonic frequencies are as Willada stated they will be multiplies of the fundamental and the timings of these reflections. We can determine the time the projectile takes to travel the length of the barrel and can then calculate what number of harmonic frequencies need to be considered as the 50th order may still be ringing in the barrel long after the projectile has left. The projectile may have left before the 7th reflection has had time to occur.
I am not in any way saying that the barrel doesnt lift before the projectile leaves the barrel. I know it does. I am not entirely sure how much is in the complete gun lifting and how much is the barrel itself lifting and or moving in any other direction.
The gun jump can be easily proved by putting different weight bi pods on for instance at the front of the stock. You can hold the forestock with a downward pressure and see a difference in POI.

GSells
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Joined: Sun Aug 13, 2017 11:04 pm

Re: More on Barrel Tuners

#112 Postby GSells » Thu May 31, 2018 8:01 pm

So David , in neonandathal speak , for mid to longs we want our groups to be slightly skinny rather than fat ? Ie " sneaking up on an anti node " :shock:

GSells
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Re: More on Barrel Tuners

#113 Postby GSells » Thu May 31, 2018 8:07 pm

For all of the newbies out there , I can highly recommend some Panadol,
Warm soup and maybe some Chocolate, ( others may say a stiff Rum ), after than brilliant but brain bending explanation of barrel harmonics !!

My Head doesn't hurt as much as it use to lol!

Thanks David for your writings, I would be selfish to say , I wish we could just keep this knowledge to ourselves ( Australians ).
But that would be wrong!

GSells
Posts: 335
Joined: Sun Aug 13, 2017 11:04 pm

Re: More on Barrel Tuners

#114 Postby GSells » Thu May 31, 2018 8:59 pm

Gyro wrote: My own experience with muzzle velocity variations reveals just how easily it changes, even with the gun handling.

Yep I've found u can get huge velocity changes , whether u free recoil , semi free recoil ( what I do ) or preload ( like I do with my Omark .308)30 fps from my experience.

I used to watch Cam Mac shoot his 284 ( Raton rifle ) and used to free recoil it , and it used to rifle torque like a bucking bull ! But he was consistent with it and he used win like that !

There was a video on this site circa 2014 of him shooting it , posted by Ecomeat I believe .

Just a mention about extreme spread and standard deviation ( for the newbies ) sd is going to tell u what's going to happen and es will tell what happened .

Barry Davies
Posts: 1181
Joined: Tue Aug 24, 2010 12:11 pm

Re: More on Barrel Tuners

#115 Postby Barry Davies » Fri Jun 01, 2018 8:37 am

How can the way you handle a rifle have an effect on muzzle velocities?
Barry

Wal86
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Joined: Sun Nov 20, 2016 5:10 pm
Location: Kilmore, VIC

Re: More on Barrel Tuners

#116 Postby Wal86 » Fri Jun 01, 2018 9:16 am

Barry Davies wrote:How can the way you handle a rifle have an effect on muzzle velocities?
Barry


Im curious to this aswell Barry... One of my Heavy bench rifles was 120lb and there was minimal recoil, we actually reduced the rifles weight by 45lb to allow it to recoil substantially more, muzzle velocities did not change at all..

Cheers
Last edited by Wal86 on Fri Jun 01, 2018 4:11 pm, edited 1 time in total.

AlanF
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Location: Maffra, Vic

Re: More on Barrel Tuners

#117 Postby AlanF » Fri Jun 01, 2018 10:11 am

Wal86 wrote:...One of my Heavy bench rifles was 120lb and there was minimal recoil, we actually reduced the rifles weight by 45lb to allow it to recoil, muzzel velocities did not change at all...


Theoretically, all else being equal, a lighter rifle will recoil more and muzzle velocity will decrease. Maybe you used a Magnetospeed to measure velocity? Being fixed to the barrel it won't see any difference.

Barry Davies
Posts: 1181
Joined: Tue Aug 24, 2010 12:11 pm

Re: More on Barrel Tuners

#118 Postby Barry Davies » Fri Jun 01, 2018 10:56 am

Alan,
Maybe, theoretically, but the question was with respect to " handling " not rifle weight.
Barry

Wal86
Posts: 150
Joined: Sun Nov 20, 2016 5:10 pm
Location: Kilmore, VIC

Re: More on Barrel Tuners

#119 Postby Wal86 » Fri Jun 01, 2018 11:15 am

Barry,

Yes, i understand your question, but weight effects rifle behaviour.. Both weights were total free recoil the only resistance was its own weight...
This was something i tested 15yrs ago, ive also re tested this when the first lab radar came out, and got the same results, as i was skeptical about the accuracy of chronographs at the time..
One of the other result i got from this was that a rifle must recoil...
Just a thought,

Cheers
Last edited by Wal86 on Fri Jun 01, 2018 8:09 pm, edited 1 time in total.

williada
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Re: More on Barrel Tuners

#120 Postby williada » Fri Jun 01, 2018 12:20 pm

Sungazer the models out there are generalized but there are some truths in what is said. If you look at the speed of sound passing through steel its closer to 19,000 fps. That means the speed of the vibrations are a lot quicker than your projectile. While the interference waves are stress waves mainly in the longitudinal plane to give us the fundamental lift there is vibration and the changing hydraulic pressure of the air inside the barrel added to torsional effects and changes in friction even when the bullet pops add to the mix. But also important is the helix path of the bullet which is not in the longitudinal plane that adds to a donut shock wave form. This means that the bolt face which closes one end of the vibration and to a lesser degree the muzzle as the end of the natural medium are not the only sources for reflection but reflected vibration occurs from the internal walls too. Combined effects make the muzzle oscillate and vibrate as well as swing. Working with your barrel's personality in the macro lift and the micro muzzle oscillation delivers the best accuracy.

If we just took the the ignition shock wave as a crude estimate of barrel time and its only one source of excitement then a 30 inch barrel may utilise the 5th harmonic as do some of Purdy prescription rimfire shooters to calculate optimum barrel time for an harmonic length. This does not mean first or second harmonics are not present etc., they are partly formed, they have not finished their cycle. You would need a very long barrel for cycles to complete. The 5th harmonic is merely a subdivision of the the 1st harmonic that is completing its cycle at the the node. We know this is a point of minimum amplitude on what is effectively the dominant wave, so in theory we would expect this point to have less muzzle movement. This is why round groups form close to a node. An High power is a different ball game and all the other sources of vibration are amplified. Their sub frequencies may destruct and construct stress waves to add to the mix. Muzzle distortion is the accuracy killer.

We want minimum distortion. We can achieve that with the heat sink of a fixed weight like Cam McEwan used or a taper lap and crown ant the minimum bore size or cut a barrel back to get the right harmonic length as examples of traditional methods. Or we can change the frequency of these very quick vibrations through the use of a tuner so vibrations do not distort the muzzle or allow a little distortion to take advantage of that distortion to make the group for example less wind sensitive.

The first few harmonics are really too smooth to make the ride too uncomfortable to throw things about but they generate lift like swell in a fishing boat when there is no wind. In a fishing boat, when the wind gets up and the chop appears the ride is uncomfortable and things get tossed about. This is why I break down the tunes into macro components and micro components. But controlling the muzzle is the most important at the micro level rather than worrying too much about the macro lift.

There is a general relationship with ignition and the first few harmonic values in that there is a goal to have the powder fully ignited before the first impulse reflects back. That is where a jamb seating builds pressure to burn more efficiently. That is why playing with powder density and seating depth matter too. Obviously case design and short powder column matter here and the faster burning powders. Then this is relevant to sub frequencies of the fundamental frequency in that first moment of ignition excitement. Then we have to compromise with other sources of vibration which alters bore size too.

I have found reverse engineering is a more reliable to determine what is happening. The paper always tells the story. Traditional chronographs had error factors. Lab radars are accurate. When I find harmonic values of between 19 and 25 work in practice, its telling me traditional theories are missing or don't account for the interactions of all variables at the point of interest which is at the muzzle. This assumes there is no in bore yaw or other mechanical smithing issues. Gyro you have got that right and yes we can model trajectory with muzzle angle on a spread sheet with different bullet velocities and account for macro lift.

These tiny movements in the tuner do handle those finer harmonic frequencies to change their angle of reflection to bunch them together in the right place so the muzzle is not distorted.

So if we think about it, the speed of the bullet less important than the speed of the vibrations. Point two of a grain of powder extra, won't change bullet speed much, but it has a big impact on vibration speed as do small tuner movements.
Last edited by williada on Fri Jun 01, 2018 12:57 pm, edited 1 time in total.


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