1. How Far Apart Are Rifle Barrel Accuracy Nodes In The Body
2. How Far Apart Are Rifle Barrel Accuracy Nodes Made
3. How Far Apart Are Rifle Barrel Accuracy Nodes Removed
4. How Far Apart Are Rifle Barrel Accuracy Nodes Destiny 2
5. How Far Apart Are Rifle Barrel Accuracy Nodes In Neck
6. How Far Apart Are Rifle Barrel Accuracy Nodes In Women

“Now and then, 2-3 thousandths change in seating depth can make the difference between average and peak accuracy,” explains Mike Ratigan, Benchrest Hall of Famer and World Champion, in Extreme Rifle Accuracy. Wow, 0.002-0.003 inches in bullet jump can sometimes make the difference! The lands of the rifle are where the rifling of the barrel starts. If you have a bolt action rifle, you can remove the bolt and look from the rear of the rifle out the front of the barrel. You will see some spirals in the rifle barrel. The spirals give the bullet spin and help it to be more accurate. What is the bullet ogive?

Barrel Tuner Vibration Analysis:
Effects of tuner adjustments on vibration frequency
and the shift in barrel node points.

This analysis was done with the LS-DYNAFinite Element Code. This software is a very powerful tool for analyzing thedynamic and static loading of structures. It was used here to calculate theVibration Mode shapes and Natural Frequencies of a rifle barrel with a tunerinstalled and with the tuner positioned at slight different positions. Thebreach end of the barrel was fixed in space which treats the barrel as acantilever beam. There is a vertical plane of symmetry in the calculation andonly motions in the vertical plane are calculated. The displacements are greatlyamplified so that they can be viewed.

THE BARREL.... The 416 Stainless Steel barrel in this calculation hasa breach diameter of 1.5' with a constant diameter for 4' and then astraight taper to a diameter of 0.8' at a distance of 20'. Itsdiameter is 0.8' from there to the end of the barrel at 22'. Thecaliber is 6mm with no rifling modeled. The 416 Stainless Steel tuner has an0.8' ID and the OD is 1.5' and extends 2' beyond the muzzle inthe initial position. This barrel weighs 6.61 pounds and the tuner weighs 1.11pounds. Two additional calculations were done with the tuner moved 0.1' tothe right and 0.2' to the right (farther from the breach). The breach endof the barrel is fixed to simulate the barrel's attachment to the rifle'saction. For ease of generating the 3-D model, I did not include the cartridgechamber or the thread ligament.

HOW ACCURATE ARE THE CALCULATIONS?.... I have run a couple of testcases comparing the FEA results with classical methods of analysis for modeshapes and frequencies. The deflection (sag) calculated with FEA is checked foraccuracy. Accuracy Comparison.

Mode 1 - 80.304 Hz

Mode 2 - 439.22 Hz

ADDING A TUNER.... Adding a tuner to the muzzle of a rifle barrel doesthe following:
1. The additional mass reduces the amplitude of the vibrations.
2. Decreases the natural frequencies by decreasing the lower Mode's frequenciesmore than the higher Modes.
3. Increases the barrel's vertical end sag due to the extra weight. This wouldtend to make the vertical plane the preferred plane of vibration.
4. Moves the Mode 2 node closer to the muzzle.

POSSIBLY MODESHAPES ARE NOT SO IMPORTANT.... I ran some FEA calculations of how a barrelreacted to the high gas pressure and recoil. The forced deformations from thehigh pressure gas and recoil cause the muzzle to change where it is pointing atthe target when the bullet exits the muzzlet. Click on the graphic to read theinfo on Esten's rifle. Esten did extensive testing so that the FEA model couldbe normalized to his test data.

Click here or on the graphic to view the calculationresults.

COMPLEX VIBRATION.... The top animated gif is Mode 1 of the barrelwith a tuner and the Mode 1 vibration frequency is 80.304 Hz. The bottom view isMode 2 vibration that has a frequency of 349.22 Hz. The ratio of the frequencyfor Mode 2 to Mode 1 is approximately 4.34 to 1.0. I have tried to make theanimations with that same frequency ratio so the viewer can visualize thecomplexity of what is occurring with the barrel and especially the displacementof the muzzle and the angle of departure of the bullet. In your mind's eyeimagine the two modes of vibration going on at the same time with the amplitudeof Mode 1 larger than Mode 2. As the larger swings of Mode 1 are occurring thesmaller but faster amplitude swings of Mode 2 are superimposed on Mode 1.

ADJUSTING THE TUNER.... As the tuner is adjusted by moving it fartherto the right on the barrel (farther from the breach), the frequencies of bothmodes decreases. Here is a table of the resulting Mode frequencies as the muzzletuner is located at the original position and then moved to the right 0.1'and then 0.2'. A separate calculation was done with the tuner removed as abase condition which has a much higher frequency in both Mode 1 and Mode 2 but alower frequency ratio of Mode 2 to Mode 1 of 3.804. Not only does the tunerlower the frequencies, but it changes the ratio between the two frequencies.

Table 1: Mode Frequencies

MODE 2 NODE LOCATION.... For the tuner in the original position, thenode where the barrel's center line stays on the original axis is 1.60'back toward the breach from the muzzle. You can view the location in theanimated gif picture. Find the node location by putting your mouse pointer onthe center of the bore and move it to the right or left until the verticalmotion of the center of the bore remains fixed behind the mouse pointer. Thetuner mass would have to be moved much farther away from the breach to cause thenode to be located at the muzzle.

BARREL SLOPE AND CURVATURE.... In this view, I placed a dotapproximately at the node point. At the muzzle upward swing of Mode 2, the slope(first derivative of displacement) of the barrel is positive on both sides ofthe node. The change in slope or curvature (second derivative of displacement)is also positive on both sides of the node. The bore is not parallel to the axisat the node location. The only time the bore is parallel to the original axis iswhen the barrel swings through the rest position. At that time, of course, everypoint on the barrel is parallel to the axis. The same is true for Modes greaterthan Mode 2, at each central node. The bore is always parallel to the axis atthe anti-nodes (minimum and maximum) points between the nodes.

How Far Apart Are Rifle Barrel Accuracy Nodes In The Body

SIMPLY WRONG.... There is an article on the web from the PrecisionShooting Magazine that is wrong about how a barrel vibrates. Here is thearticle: I'mFeeling Those Good Vibrations, AGAIN! A barrel tuner can improve accuracybut this article is wrong about how a barrel vibrates and how tuners work.

EXIT ANGLE.... If the tuner were long enough to cause the node of Mode2 to be located at the muzzle, the muzzle would still have the variations inexit angle and the exit angle would not be parallel to the original bore axis,except when the barrel passes through the rest position twice on each cycle.

BARREL SLOPE WITH NO TUNER.... The dot is approximately at the nodepoint. Zooming in at the Mode 2 node while at the muzzle's maximum upward swing,the upward slope and positive curvature is more obvious in the barrel withoutthe tuner.

Table 2: Mode 2 Node Location

How Far Apart Are Rifle Barrel Accuracy Nodes Made

Mode 1 -130.91 Hz

Mode 2 -498.00 Hz

TUNER REMOVED.... For a base condition, here are thefirst two vibration Modes for the same barrel with the Tuner removed. The barrelvibrates with approximately a 38% higher frequency with the Tuner removed. Thevibration frequency of Mode 2 is slightly less than four times that of Mode 1.The Mode 2 node is much farther back from the muzzle.

Possible explanation of howa tuner could improve accuracy

MUZZLE POSITION.... The Tuner lowers the frequencies ofeach Mode so that the muzzle could be just approaching the upper extreme of itsswing at the time the bullet exits. The Tuner also adds weight to the barrel'smuzzle which increases the vertical deflection (sag). More sag before firingwould make the barrel more likely to vibrate in the vertical direction.

MUZZLE EXIT ANGLE.... Tuner changes the frequency of eachmode when it is adjusted and not at the same rate. The exit angle is probablymore important to shot placement than the vertical position of the muzzle. TheTuner could be adjusting the muzzle exit angle so that when the deflections ofMode 1 points up, the Mode 2 is pointing down. This could be happening at thetop or bottom of the Mode 1 muzzle swing.

How Far Apart Are Rifle Barrel Accuracy Nodes Removed

TIMING.... The approximate time that it takes a 3300 fpsmuzzle velocity bullet to exit the barrel, assuming a constant acceleration, is0.0011 seconds. Actual exit times would be longer since the bullet is not underconstant acceleration and the time from the firing pin first hitting the primer,ignition starts, is not included.
The view is a typical pressure vs. time trace from RecreationalSoftware, Inc. Note that the zero time starts at a 12,000 psi pressure andbullet exit is somewhere near the + signs. The primer ignition was at an earliertime. The velocity of sound in 416 stainless steel is 14,900 fps and a stresswave has time to propagate up and back the full length of the barrel 4 or moretimes after ignition and while the bullet is traveling within the barrel. Themuzzle end of the barrel has ample time to 'know' that something isgoing on at the breach end before the bullet exits.

VIBRATION PERIOD.... As an example, assume a mode 1frequency of approximately 100 Hz that has a period of vibration of 0.010seconds. Therefore the time it takes the barrel to make its first upward swingis a fourth of a period or about 0.0025 seconds. This is the approximate timethe bullet exits. The mode 2 vibration has a period of approximately 0.0002seconds and could be at the top of its thirteenth upward swing, at the 12.25^thperiod swing, or about 0.0025 seconds. These two modes could add and amplify theexit angle of the muzzle near the peak of its upward swing, just as the bulletexits. The tuner could be adjusted to slightly change the two frequencies sothat they reinforce each other at the time of bullet exit.

FINDING THE SWEET SPOT.... When tuning a load to aparticular rifle, possibly the sweet spot is not when the bullet exits thebarrel at the maximum of the vibration's upward swing but, slightly beforethe maximum height or exit angle of the upward swing.
UPWARD SWING.... The vertical amplitude of vibration is more heavilyexcited than the horizontal vibration because the center of gravity of the rifleis located below the barrel's centerline and the bullet's travel down the barrelcauses a vertical turning moment about the rifles center of gravity. Thevertical vibration is most important. Also, the barrel is initially slightlydeflected downward due to gravity. When the round is fired, the pressure alsotends to straighten the barrel like a bourdon tube in a pressure gage. As thebarrel straightens, it over shoot in the upward direction and this adds to theexcitation of the Mode 1 vibration. As a side note, the axial extensionvibration mode is also probably heavily excited. This is the mode where thebarrel extends and shortens axially. But, this axial mode should only have anegligible affect accuracy.
AVERAGE VELOCITY BULLET.... Possibly the sweet spot occurs when thebullet, with the average velocity, for a particular load, exits the barrel justbefore the peak of its upward swing.
FASTER BULLET.... A faster bullet will exit the barrel earlier and exitslightly before the average velocity bullet and the angle of the upward swing ofthe barrel will be slightly less. So the bullet's launch angle is slightly less,but the bullet is going faster and drops less.
SLOWER BULLET.... A slower bullet will exit later and the barrel'svertical swing will be higher and at a steeper angle when the slower bulletexits. The bullet is launched at a higher angle but is slower and will dropslightly more.
This combination, within limits, would print the bullet at about the samevertical location on the target for the normal variations in velocity from roundto round.

Mode 1 -80.304 Hz

Mode 2 -439.22 Hz

Mode3 - 919.5 Hz

Mode4 - 1790 Hz

Mode5 - 2374 Hz

FIRST FIVE MODE SHAPES.... These are the first fivevibration Mode shapes, in the vertical plane, that the barrel and tuner undergowhen excited. The displacements are shown here greatly amplified so the shapechange can be easily seen. The actual displacements are very small and evensmaller at the higher frequency Modes.

Good Hunting... from Varmint Al

For the serious reader: How toCheck Another Engineer's Calculation.
More info on ModalAnalysis.

Last Updated: 02/08/2013
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How Far Apart Are Rifle Barrel Accuracy Nodes Destiny 2

Introduction

The debate of whether the 5.56x45mm round is effective in the M16 platform has been around since they first came into service, replacing the M14 which sported the 7.62x51mm cartridge. The round and rifle have both proven themselves in the last 50+ years, and the debate (mainly) has been put to rest. In this post, I wanted to touch on the specifics of the 5.56mm round, and then discuss the round in Short Barrel Rifle applications, especially since they have been increasing in popularity as Personal Defense Weapons (PDWs). For the sake of simplicity, I will refer to the 5.56mm, but the same information applies to .223 rounds as well, although you should never shoot 5.56 ammunition in a rifle chambered for .223, while a weapon chambered in 5.56 can accommodate both 5.56 and .223.

5.56x45mm Wounding Mechanisms

The round is very effective in certain scenarios because of two effects not seen in most other rounds: tumbling and fragmentation.

Tumbling

At the proper velocity, the round tumbles and yaws when it enters the body, causing massive damage to the immediate and surrounding tissue. This creates a massive wound channel.

Fragmentation

As the round tumbles, it also breaks apart, with the smaller pieces diverging out and further damaging surrounding tissue.

How Far Apart Are Rifle Barrel Accuracy Nodes In Neck

These two wounding mechanisms are how the round overcomes its shortcomings compared to other larger and heavier rounds. These mechanisms, however, are linked to velocity. Under a certain velocity, the round fails to tumble and fragment, in which case the main damage seen is a .224″ hole in the body.

Velocity and Barrel Length

Many people believe that shorter barrels are less accurate than longer barrels. This is false. In reality, shorter barrels result in lower velocities for the exiting bullet. Inside the casing, the primer detonation ignites the gun powder. As the powder ignites and heats, the gas inside rapidly expands, propelling the bullet down the barrel. Think of it as expansion of gas, not an explosion. The 5.56 was designed for the M16, which features a 20 inch barrel, and the bullet uses all of this length to get up to a velocity of 3,000 feet per second. So as the barrel length is decreased, the bullet exit velocity also decreases, since the gases don’t have enough time to get the bullet up to speed before the bullet is expelled. Here is chart showing barrel length vs velocity for the 63 grain M855 round (image courtesy of safedefensejournal.com):

Note the red line on the chart. Below this 2500 ft/sec, full metal jacket rounds will not reliably fragment. Basically, any AR with a barrel under approximately 9.5″ will never be able to expel a projectile over fragmentation velocity. A 10.5″ barrel will launch a projectile over this barrier, but air resistance/drag will quickly slow it down to under frag velocity in around 25-50 yards. Even going with an 11 or 12 inch barrel will still only get you to around 75 yards max. By the time you get a little longer, you effectively lose the advantage an SBR altogether.

At this point, if you have an SBR or AR pistol, you are probably getting depressed. You’ve put in a lot of money and time to get a cool tool that you would bet your life on. You may even be shooting sub MOA at 100 yards and now you think it wouldn’t be effective at that range. Well, a .224″ hole through your body is not something you easily walk away from. But, there is additional consideration: ammo selection.

Ammo

Up to this point, all we have discussed is the military application of these rounds and rifle combination. The military has its hands tied with the Hague Convention (commonly misattributed to the Geneva Convention) which states that we will not use expanding or hollow-point ammunition in a war environment. Luckily, civilians are not bound by these rules and can run a variety of ammo.

The best choice for self defense ammo in SBRs is the expansive variety: Hollow Points (HPs), Soft Points (SPs), and copper expanding bullets are all good options for your load out. I would advise to stay away from Open Tip Match (OTM) rounds, as most were primarily designed for superb accuracy and a super flat trajectory, but not for penetration or expansion. A good resource for ammo specifics can be found here: Self Defense Ammo by AR15.com

And a vast amount of info on wound ballistics and ammo choices: Wound Ballistics and Accuracy of Ammo

BarnesTSX 70 gr Copper Projectile

My Rifle

My SHTF weapon is a 10.5 AR-15 SBR in 5.56. I do have a 300 Blackout in the same length that I would prefer, but finding ammo if I was forced from my home would be near impossible. And even if I ran out of my expanding ammo for the 5.56 and had to use milsurp ball ammo, it would still beat throwing rocks. You may ask why I wouldn’t choose my 16″ AR-15 for my get-out-of-Dodge weapon. For starters, if I were to need to use my weapon in a defensive situation, it would be close quarters, as anything farther would warrant Escape and Evasion maneuvers, in which an SBR would be more handy. Also, after doing a few bug out drills with that rifle which included 10+ miles of humping my ruck and weapons, I decided having something light and maneuverable was more important than a few hundred FPS. Ounces equal pounds, and pounds equal pain, as they say.

Summary

After you have chosen some ammo, make sure your rifle eats that ammo like candy. It wouldn’t hurt to pick out a few different types of ammo (FMJ, HP, SP) and stagger them in your magazines. The FMJ would suffice if you need penetration through an object first (glass, door, etc.) then the expansive type for direct contact. No matter what you choose to keep for your SBR, range time and training are always just as, if not more, important. In the words of Wyatt Earp, “Fast is fine, but accuracy is final”.

Stay Frosty.

How Far Apart Are Rifle Barrel Accuracy Nodes In Women

References/Additional Reading