5 or 3 shot group when determining ES/SD???

[J E Custom]

Someone in another thread stated or implied they consistently get 3-4 ES with their hunting loads.

Sometimes I don't know whether to feel completely inept or call BS.

-- richard

3 or 4 SDs is possible but rare. The big bores ( 375s, 416s and 458s)are the most likely because
of bullet weight. (less affected by subtle pressure changes)).

I personally have never owned a rifle smaller than a 416 that could prodeuce SDs that low
consistently

I try to get into the single digits (09-) but am very happy is I get 12 or less.

All barrels have some whip or twist when fired. the heavier the barrel the less it does this.

The "Node" that was referred to is simply the most consistant harmonics.(If the barrel does
the same thing every time it will be more consistant/(Accurate in most cases).

As was stated . There is no one and only way to find the best load. I found that starting with
the chronograph saved lots of ammo and barrel ware for me.

Also I will try any load that is recomended by a fellow competitor and sometimes they have
worked out but most of the time not as good as I expect, and as we all know each rifle/barrel
is different and likes what it likes.

There are standard known accuracy loads that will work well in some rifles but not in all,so
testing is the name of the game.

J E CUSTOM

 

[Bart B]

Find a load that offers good accuracy and consistency and be happy. Good velocities are #2 and low ES are #3. A load that offers the best harmonics possible is worth more than low ES (IMHO). Find good harmonics and you will be a successfull longrange marksman.

The "Node" that was referred to is simply the most consistant harmonics.(If the barrel does the same thing every time it will be more consistant/(Accurate in most cases).

Please, folks, get in touch with a mechanical engineer who's knowledge and skills are what you trust.

They'll tell you that a given barreled action has the same fundamental frequency (maximum whip angle of the bore at the muzzle) and harmonics (exact multiples of the fundamental but insignificantly small in amplitude) for each and every round fired. That happens 'cause the barrel steel's still the same stuff and so are its dimensions for each shot. The low frequency it whips at as well as the multiple harmoncs (2x, 3, 4, etc. the fundamental frequency) are exactly the same for each round regardless of how its loaded. The only difference is the magnitude of the whip, but that' doesn't change more than an insignificant amount.

A rifle barreled action is exactly like a guitar string when plucked with a pick or finger; it vibrates at the same note (frequency) each time. Only the loudness (how much it swings back and forth making sound waves) changes directly with how hard or soft it's plucked.

All this stuff about "harmonics" is grossly misunderstood by 99.99% of all rifle shooters. Once the rifle's built, its barrel whip frequency and harmonics thereof don't change......ever!!!! Shoot a round or smack it with a ball peen hammer; it vibrates the same for each.

 

[rscott5028]

J E,

Just so that I understand clearly... Are you saying that as a fairly successful F-Class shooter, you will settle for an accurate load that consistently produces strings with a standard deviation (SD) of 12 or less fps?

...not extreme velocity spread (ES) which could actually be a bit more?

As always, we appreciate your input.

Thanks,
Richard

 

[rscott5028]

Thanks all for the discussion. I may actually be learning something here...

I use the Shooting Chrony knowing it's not precision lab test gear. Nonetheless, it fit my budget. Here's an excerpt from the manual...

USER'S MANUAL

Accuracy: 99.5% or better. Displayed velocity will not differ from actual velocity by more than 1 part in 200, i.e., ±10 fps on a velocity reading of 2000 fps. Typical performance is generally better, and shot-to-shot repeatability is always more accurate, i.e., Reported Mean Instrumental Velocity may differ by as much as 0.5% from actual mean instrumental velocity, but Standard Deviation calculated from data gathered with a Chrony will always be closer than 0.5% to actual Standard Deviation for a string. This is an important fact because an accurate measurement of a load's uniformity is of considerably more importance than is an exact measure of its average velocity.

So with actual velocity around 3000 fps, it could read 15 fps high or 15 fps low.

But for a given shot string with consistent lighting and setup, it should measure each shot more consistently. i.e. It may not know exactly how fast they're going, but it pretty much knows how much faster or slower this one is compared to the previous one. Hence, the SD won't be off by nearly so much.

That to me is another good argument for longer shot strings when I get to the final proving stages of my load. Hopefully, I'm shooting long range at the same time by then as well.

-- richard

 

[Bart B]

They'll tell you that a given barreled action has the same fundamental frequency (maximum whip angle of the bore at the muzzle) and harmonics ...

Oops!!! I should have said "...has the same fundamental frequency (whip frequency of the bore at the muzzle) and harmonics..."

Hope I'm not the only one in this forum that's made an error, but at least I got it corrected.

 

[Bart B]

So with actual velocity around 3000 fps, it could read 15 fps high or 15 fps low.

There's one other variable that'll cause errors between measured velocity and actual velocity. It's us humans who don't hold the rifle against our shoulder with the same force/pressure for each shot. I've seen as much as 50 fps difference between two people chronographing the same load in the same rifle. And both of us could easily cause a 20 fps error by holding the rifle against our shoulder a little bit different for each shot. I could vary average velocity as much as 40 fps without much effort.

So I'm convinced that shooting a centerfire rifle off the shoulder as it rests atop something on a bench ain't accurate to less than 5 fps, maybe even 10 fps for some folks. Results from rifles fired from a machine rest show much less extreme spread and lower standard deviations. No wonder SAAMI uses hard-mounted universal receivers and test barrels to measure velocity data to eliminate as many variables as possible.

The good news is our handloads probably produce smaller velocity spreads than we typically get with chronographs' data from bench-fired rifles. The bad news is we gotta shoot more rounds to get a more accurate data for both SD and ES

 

[J E Custom]

J E,

Just so that I understand clearly... Are you saying that as a fairly successful F-Class shooter, you will settle for an accurate load that consistently produces strings with a standard deviation (SD) of 12 or less fps?

...not extreme velocity spread (ES) which could actually be a bit more?

As always, we appreciate your input.

Thanks,
Richard

My goal for target/match shooting, especally at longer distance has been single digits. Most of my
match rifles have loads in the 5 to 7 SD range some of my hunting loads will/can have a little more
for shorter distance and will still be accurate at 5 or 600 yards. I prefer to have all single digit
SDs when possible no matter what the distance on all of my rifles but some will just not get there.

Shooting 1000 yard, 2000 yard creedmoor,f class or palma matches you will not be competitive
unless you have good SDs and a rifle capable of sub MOA at distance and preferably 1/2 MOA
so I don't settle for anything but the best the rifle/load can do.(I wan't the rifle to be better
than Me).

SDs are the average of Extreme spread (As you said) and if you can get the ES below 10 in a 10
shot string,you are home free.

For a compairson= My hog rifle has never been Chronographed because at less than 200 yards
(The max distance it is used because of the thick brush) accuracy is all that counts and velocity
spread does not matter that much. But on a rifle that is expected to perform beyond 200 yards
the rule changes as distance goes up.

J E CUSTOM

 

[Michael Eichele]

Please, folks, get in touch with a mechanical engineer who's knowledge and skills are what you trust.


A rifle barreled action is exactly like a guitar string when plucked with a pick or finger; it vibrates at the same note (frequency) each time. Only the loudness (how much it swings back and forth making sound waves) changes directly with how hard or soft it's plucked.

All this stuff about "harmonics" is grossly misunderstood by 99.99% of all rifle shooters. Once the rifle's built, its barrel whip frequency and harmonics thereof don't change......ever!!!! Shoot a round or smack it with a ball peen hammer; it vibrates the same for each.

Fair enough. I can't say I dissagree with these statements except that I don't think I need to seek the advice of another engineer or that 99.99% of all shooters grossly misunderstand harmonics and that I believe frequency intensity can be different when different varibles are interjected. In other words, heavier or lighter bullets with a bigger or smaller internal explosion will cause more or less intensity as well as different wave node locations. The point I am trying to make is that the bullet still has to exit the barrel at a given point in the 'frequency' for best results. Also, you can't compare a guitar string to a rifle barrel. One has a fixed boundary and the other has an free boundary.

When I refer to 'harmonics' on this site, I am referring to the frequency of barrel whip you describe. There will always be a dead or neutral point(s) (AKA: 'wave nodes') on the barrel as well as a maximum amplitude. Max amplitude occurs between the wave nodes. Exit the bullet at max amplitude ('anti node') and the results suck. Exit the bullet when the barrel is in line with the 'wave nodes' and life is good.

I think it is you who said that you had experienced high hits at 1K with lower velocities and hit lower with bullets going faster. As you stated, this was due to 'barrel whip' I understand this principal. The bullet is exiting the muzzle while various points of the barrel are in the 'anti node' point in the frequency. The anti node is the point where the amplitude of the sine wave is at its maximum. That said, if you exit the bullet at the right time for that frequency the effects of high hits for lower velocities and vice versa is eliminated. The bullet needs to exit when the whole barrel is on the same sheet of music with the wave nodes for the best possible results. If you can find that sweet spot, it is typically referred to as the 'harmonic node'.

You can illustrate the point I am trying to make by holding an arrow (this works best with no insert or tip) horizontally with one hand by the nock and tapping the arrow in the middle of the shaft. You will feel the vibrations with the hand that holds the arrow. As you tap closer to the open end of the shaft (free boundary) the frequency becomes less intense. When you get to a certain spot, there is a 'dead' spot or 'node'. All you feel is the tap of your finger and NO vibrations (AKA: 'frequency'). Then, when you pass this dead spot itself, you feel the harmonics again. There is also a dead spot between the middle of the shaft and your fingers holding the arrow. When you interject an insert and tip, this dead spot or node moves with different weights on the head. The heavier the weight on the end of the arrow, the closer to the end the dead spot will be. Target archers typically want their arrow rest on or very near this dead spot (AKA: 'wave node') for the most forgiving launch. These dead spots are 'wave' nodes. There is a point during the frequency wave where the whole arrow shaft is straight and in line with these wave nodes. In other words, there is a time during the frequency when the arrow is straight. If you can visualize that, then you can see why you want a bullet to exit the muzzle when the barrel frequency is at 0 amplitude.

I am sorry if I did not use the right 'verbiage' in a previous post to lead you to think I need to consult an engineer.

Are you an engineer?

M

 

[Bart B]

I think it is you who said that you had experienced high hits at 1K with lower velocities and hit lower with bullets going faster. As you stated, this was due to 'barrel whip' I understand this principal. The bullet is exiting the muzzle while various points of the barrel are in the 'anti node' point in the frequency. The anti node is the point where the amplitude of the sine wave is at its maximum. That said, if you exit the bullet at the right time for that frequency the effects of high hits for lower velocities and vice versa is eliminated. The bullet needs to exit when the whole barrel is on the same sheet of music with the wave nodes for the best possible results. If you can find that sweet spot, it is typically referred to as the 'harmonic node'.

Are you an engineer?

I also stated that some shots at higher velocity struck low; I had put each group into thirds of all shots fired.

Even if every bullet left at exactly the same speed at exactly the same point in the vertical whip of the barrel, they'll still have vertical dispersion. That's due to the bullets small spread in BC; they all ain't the same 'cause they ain't all perfectly balanced. The more unbalanced ones will have more drag and therefore strike lower. There' typically no more than 1.5% spreads in BC, but that's enough to cause 1/4 MOA vertical spread at 1000 yards.

I think you mean the barrel, when at it's node, it's straight and at the mid point in its whip cycle. I don't think anybody can guarantee that'll ever happen as the bullet exits and nobody's ever proved it as far as I know. Spark photograph tests decades ago showed an M1903 Springfield's bore axis at the muzzle was moving upward and close to the top of its whip when the bullet exited. With most rifle barrels bore axis at the muzzle whipping at their fundamental frequencies of 60 to 100 Hz, they go through one cycle in about 17 to 10 milliseconds (other harmonic frequencies are higher and have much, much smaller magnitudes). Barrel time from case mouth to out the muzzle for most rifle bullets is only about 1 to 1.5 milliseconds. And the angular speed of the muzzle axis' whip at this node or zero point is the fastest; it's the slowest at the peak and valley of the wave.

Here's a link that'll help explain how a barrel whips. Check out all the site's links to barrel movements when they're whipping about.

Barrel Harmonics Mode Shape Movies

No, I'm not an engineer any more. But that doesn't matter.

 

[Michael Eichele]

Well put Bart. That link was excellent as well. Thank you.

I think between what you have been saying and what that link illustrates is that we share the same understanding of this subject more than you might think. At least principally. We can argue about when the best time for the bullet to exit the barrel but that is really a mute point. I think we can both agree (as well as most of us here) that there are definate 'sweet' spots as to where the bullet is in the barrel (or exiting) at a given time during the harmonic cycle.

In any event, I think we share the same basic understanding and principals here.

M

 

[rscott5028]

Well put Bart. That link was excellent as well. Thank you.

I think between what you have been saying and what that link illustrates is that we share the same understanding of this subject more than you might think. At least principally. We can argue about when the best time for the bullet to exit the barrel but that is really a mute point. I think we can both agree (as well as most of us here) that there are definate 'sweet' spots as to where the bullet is in the barrel (or exiting) at a given time during the harmonic cycle.

In any event, I think we share the same basic understanding and principals here.

M

It's going to take me a while to digest all of this and put it into perspective.

But the good news is that we don't have to fully comprehend everything that's going on. We just need to methodically go about finding a "node," "sweet spot," or whatever you want to call it.

By the same token, you don't have to have a chrony, and it doesn't have to be precise to be useful. But, it can be a useful tool when used appropriately.

Ultimately, it's accurate and repeatable performance within the context of your shooting discipline that determines whether you have a good load.

Thanks for the info everyone!
richard

 

[shortpants]

BINGO Richard!

I'm going to continue to strive to gain as much knowlege about long range hunting because it has become an obsession for me. I'm going to continue to improve my equipment to the best I can afford. With good equipment and brainstorm of knowledge I will continue to try and better my abilities as a shooter and hunter. I will never be an engineer and never understand half of what they know. If I can't control it I really don't care but that's just me. If I can improve it I'm all ears. I have nothing but respect however for those who do understand these things. It is from them that we learn the most. When it comes to knowlege these guys are pushing the limits always just like the rest of us are doing with our shooting.

Call it node, sweet spot, or whatever I'm going to try and find it and then load the ammo as consistently as possible and hope for the best. Without all you guys I wouldn't even understand that much so thankyou! I will use a chrono as another tool to help track consistency knowing it by itself is not perfect. As long as you all will let me I'll keep asking questions. Who knows maybe someday I'll be making hits on real long range targets and not just steel or paper.

Ok I'm done.

 

[Bart B]

Call it node, sweet spot, or whatever I'm going to try and find it and then load the ammo as consistently as possible and hope for the best.

Good idea. Just don't spend too much time getting cases and bullets "perfect" to the nth degree. A farily decent rifle will shoot sub 3/4 MOA all day long at 1000 with brand spankin' new cases and good bullets right out of the box. Use medium speed powders and stay away from magnum primers. Use Redding or RCBS full bushing dies in a decent press and you'll do just fine.

 

[shortpants]

Thanks for the advice Bart.