Barrel whip vs harmonics and timing question

[BalisticsNut]

Ok, I am relatively new to reloading, going on my second year. I have a .300 WSM and .243 Winchester that I reload. I am obsessive as you can tell by my given nickname. I am trying to understand more about barrel harmonics and timing and pressure. Most of what I have found has been research, trial and error. Blame it on Alliant RL-17 Powder. This is where it started. I use RL17 for my .300 WSM and have been happy with the results. Took a lot of trial and error because pretty much all reloading manuals except Alliant's has no data on RL-17. After I purchased my .243 I started experimenting with IMR4320/4350 RL17/RL15 following the book as much as possible. Mind you, Sierra's book vs Nosler's book vary on what is max powder levels so I have to work up slowly. I am careful with this type of reloading.

Here is my thought process and need verification. For my .243 I can shoot Nosler 55gr vamint loads with IMR 4320 and shoot sub MOA at 200 yards pushing 4000FPS. I can not do the same with RL15, close but not as close. Another example, recently found. Today I tried RL15 with a 90gr BT and light charges 3000FPS but could not get any consistancy at all. The groups were probably 5" spread but high, low, right etc. Not what I would call related to barrel harmonics. This is where my questions comes in along with my theory.

Using a Nosler 90gr BT
If I was to do a ladder test with IMR4320, I would assume I would see rising bullets until they grouped I would assume around 3100-3300FPS.
if I was to do a ladder test with RL-15, I would assume I would see not only rising buy bullet patterns varying left and right until they grouped in height only.

Theory IMR 4320 burns slower therefore the bullet has time to exit the barrel at the right point in time in relation to barrel harmonics and sonic propulsion from the powder without disturbing the balance of the bullet.
Theory RL15 burns too fast for this bullet therefore the harmonics and sonic propulsion would never time together, causing the bullet to destabilize upon exiting the barrel not because of barrel harmonics but because of sonic explosion upon exit.
This would explain why the RL15 powder produces random bullet patterns and IMR4320 produces tighter groups.

Am I on the right thinking path and understanding of barrel whip/harmonics and timing?

 

[Desert Fox]

Am I on the right thinking path and understanding of barrel whip/harmonics and timing?

Your questions can be answered herehttp://www.varmintal.net/amode.htm

 

[BalisticsNut]

Am I on the right thinking path and understanding of barrel whip/harmonics and timing?

Your questions can be answered herehttp://www.varmintal.net/amode.htm

Ok, well not really. I understand barrel whip and harmonics. My question was more about fast burning powder causing a sonic disturbance behind the bullet as it exits vs a slower burning powder that has not fully expanded by the time the bullet departs the chamber. Barrel whip seems to cause the bullet to rise and fall more then drift from left to right. So, if your groups are drifting left to right with the exact same powder charges and FPS, one would guess that the problem is not barrel whip but powder burn rates.

Does that clarify my question vs my theory. >>>??

 

[onesonek]

I don't think there is correlation in the context you are inferring BN.
Each rifle is as individualistic as people themselves. Harmonics are what I believe to be the main cause. Generally speaking, harmonics are changed with different pressure curves, brought about by different powders and thier particular burn characteristics. And I don't know that one can really conclude, that the muzzle blast sways either way. If all shoot terrible, then you most likely have a crown issue, other even issues in the chamber and throat areas. But that is not your case as it sounds.
Trying to gain some rational correlation with different bullets weights, and even different manufactures of the same weight with different powders, would seem almost futile to me. But that's just my opinion.
You very well may see some change, in a ladder. But if your rifle don't like that particular bullet powder combination, most often there is little one can do to correct it. But then it don't sound like you loaded a full ramp with the 90 gr./R15. I would do that, although a 5" group don't sound promising.
Albeit, you can try change the harmonics by altering (add or remove ) pressure points on the forend of the stock.
It is best just to try more powders, to see if you can find one it likes. Then look to stock alterations as a last resort. But that would likely mess up your 55 gr. load also.

Just don't over think it,,,,, and proceed with caution as usual.
Hope this helps,

 

[Guest]

It's an interesting idea, but in reality I don't believe your theory holds up. No powder is through examsing hen the bullet exits the barrel. If it were, the bullet would stop at the point of expansion stopping because there would then be no force pushing it. Further, barrel harmonics are not simply linear vibrations. While we view it as a sine wave (and it is) te actual vibrations can be oriented in any plane, and can even be somewhat radial in nature, as well.

I suspect what you're seeing is a poor harmonic match between the load you've tried and your rifle. The 5" group was not strictly horizontally spaced, I'm sure, which indicates vertical and horizontal spread. For reference, my 270Wby is very accurate with Accurate 8700, but also with IMR7828ssc, H4831, and H4350. That's an extremely wide range of burn rates, and these powders are accurate at varying velocities with two different bullet weights.

 

[Desert Fox]

I don't think there's a simple answer to your question. There's too many variables involved here to come up with a definitive answer. My question to you is, how careful are you when crafting your handloads. Did you chronograph your load. What were your SD, and your ES.
Both of your theoretical explanation of your result using IMR 4320 and Reloader 15 were flawed. To explain it simply, your rifle prefer 4320 over Reloader 15. Now there's myriad of reason why your rifle shoot more accurately with 4320 than with RE-15. It could be that the pressure generated by the 4320 were much more uniform and consistent resulting in much more uniform barrel deflection.
Barrel vibration or whip can be influenced by several factor namely, pressure from the expanding gas, barrel temperature, the torque imparted by the rotating bullet as it travel the length of the barrel and bedding. Any of these variables can have tremendous impact on the performance of your handload.

Guys, the key word here is uniformity and consistency. Make your handload as uniform as you can make them. Eliminate or control as much variables as you can and you'll have no problem finding an accurate load.

 

[BalisticsNut]

I remember reading that if a powder burns too fast, it causing the expansion of gases to burst immediately after the bullet leaves the barrel, thus creating a turbelance that can cause the bullet to destabilize. This is an understandable phenom. If I understand this correctly, a slower burning powder pushes the bullet continuously during the burning process but does not complete the burn until the bullet has actually left the barrel, thus preventing the subsonic report from causing any stabilizing issues.

i was hoping this was the case so that I could rule out powder as an issue, rather then a load workup. I also found out that RL15 is not listed as a powder of choice in any book for the .243 with a bullet heavier then 70 gr. Thus adding weight to my theory. The heavier bullet takes longer to travel down the barrel therefore causing the powder to burn in its entirity prior to the bullet leaving the chamber causing that subsonic report that destabilizes the bullet.

ok, well you cleared up one part of the theory, that a sine wave may not necesarrily move up and down but could alos move side to side or a variance of the two. This would add weight to my results on my latest shot group. But not exaactly. It seems that the two bullets that were the farthest a part had the exact same FPS thus should have the exact same sine wave action and the bullet should have left the chamber at the exact same time and the result should have been the same. how could they be 5" apart. And dont say the shooter!!! it happened twice in the three shot groups of five that I was load testing.

Any other opinions out there. Doc, how about you?

 

[BalisticsNut]

I don't think there's a simple answer to your question. There's too many variables involved here to come up with a definitive answer. My question to you is, how careful are you when crafting your handloads. Did you chronograph your load. What were your SD, and your ES.
Both of your theoretical explanation of your result using IMR 4320 and Reloader 15 were flawed. To explain it simply, your rifle prefer 4320 over Reloader 15. Now there's myriad of reason why your rifle shoot more accurately with 4320 than with RE-15. It could be that the pressure generated by the 4320 were much more uniform and consistent resulting in much more uniform barrel deflection.
Barrel vibration or whip can be influenced by several factor namely, pressure from the expanding gas, barrel temperature, the torque imparted by the rotating bullet as it travel the length of the barrel and bedding. Any of these variables can have tremendous impact on the performance of your handload.

Guys, the key word here is uniformity and consistency. Make your handload as uniform as you can make them. Eliminate or control as much variables as you can and you'll have no problem finding an accurate load.

I use a digital scale and in one of the shot groups, the FPS tested the same on two shots but those two shots were the furthest apart in the shot group. In four shots, shot 1 3102 FPS, shot 2-3077 FPS, Shot 3-3102 FPS, shot 4-3092 FPS and shot 5 3099 FPS. Shot 1 and Shot 3 3.989" a part, this was the tightest shot group of the day but only by .013". This is why i started thinking about the powder burn rates effecting the stabilization of the bullet.

Any further comments are appreciated. Love to have a good understanding why this is the case.

 

[JD338]

Guys, the key word here is uniformity and consistency. Make your handload as uniform as you can make them. Eliminate or control as much variables as you can and you'll have no problem finding an accurate load.

I think DF nailed it.

JD338

 

[Guest]

What you read about powders burning and turbulence and such seems like it's maybe, first off, way oversimplified, and second, not entirely accurate. Consider that regardless of what powder you load (as long as it's a proper burn rate for your cartridge) it will completely burn within the first 6-8" of barrel. The rest of the bullet movement down the barrel is simply from the expansion of the gases. Too slow a powder (like using IMR7828 in my 30-30WCF, for example) will result in too low a start pressure, poor case sealing, and can be evidenced by fired cases looking as though they're covered with soot from rim to mouth. Too fast a powder (like using a pistol powder in a rifle cartridge) will give you other problems like detonation due to the overall small volume of powder in a comparatively large chamber volume, which can be catastrophic. If you see RL15 listed in the powders tested, and they provide you start and max charges, you can be sure it's within the appropriate burn rate range for your cartridge.

Now, with regard to turbulence, all powders create turbulence as the bullet exits the barrel. The bullet is destabilized by that turbulence (or ~can~ be) but also destabilized by exiting from the bore, where it was being acted upon by the lands and grooves, and transitioning to free flight. This destabilization dissipates relatively quickly and the bullet "goes to sleep" as the slang phrasing goes, when it stops vibrating and settles into a nominal flight path that is your trajectory. This "going to sleep" is not the same as barrel harmonics, which I think you understand, but for the sake of clarity, I'll briefly detail here in a minute. Before a bullet goes to sleep it literally oscillates around the arc of the trajectory, meaning that the bullet is spiraling (for lack of a better way to give you a mind picture) around the single line that would be the trajectory. Over time of flight, this oscillation diminishes so as to become negligible, and the bullet is said to then be asleep. This is why some rifle/load combinations will shoot 1.1" at 100yds, but then shoot .9" at 200yds, and then shoot about 1.5" at 300yds, or some similar variation on the theme. It's because the bullet isn't yet asleep at 100yds, and so the bullet isn't traveling exactly along the trajectory, but spiraling around it. At whatever point the bullet goes to sleep, the trajectory becomes consistent and you get your best groups from there on out.

Barrel harmonics is totally different, in that it is actually a very simple phenomenon regarding vibration. When you shoot, as you already know, the barrel vibrates. Since the end attached to the receiver is "fixed" relative to the muzzle end, the muzzle end is where all the vibration exits the barrel. So, the muzzle whips back and forth in a sine wave. The trick is to create just the right combination of powder charge and seating depth for a given bullet weight to have the bullet exit the barrel at the outside edge of the sine wave, since the muzzle is perfectly still right at the point where it changes direction from going "down" to "up" or "left" to "right" or whatever orientation in which it's vibrating. Stock fit can impact the direction of the vibration and the frequencies your barrel will see, but that's another story entirely. We will assume the barrel is fully floated and stock fit has no bearing. If you're not getting the right combination of harmonics to exit at the edge of the wave, your bullets will exit along the wave somewhere, which means the barrel may be moving left/right/up/down for one shot, and moving down/up/right/left for the next, and so forth. This inconsistent exit will "throw" the bullet a bit and widen your groups. When a sweet spot can't be found for a load, it's always because the particular rifle in question, when combined with the load used, can't be adjusted to the sweet spot due to seating length extremes not allowing it. That is to say, because there's only a limited range from the minimum to the maximum COL that you can use, since the bullet has to be in the neck of the case. It is, as others have said, all about matching the powder, charge, bullet, COL, and even in some cases primer and brass case chosen, to the rifle, in a combination that gets your bullet to exit at the edge of the wave.

I hope I haven't thoroughly confused the issue, and I hope I've answered some of your questions.

DF is right, though. It's about finding the right combination, and recreating it painstakingly with utterly boring consistency.

 

[Desert Fox]

I use a digital scale and in one of the shot groups, the FPS tested the same on two shots but those two shots were the furthest apart in the shot group. In four shots, shot 1 3102 FPS, shot 2-3077 FPS, Shot 3-3102 FPS, shot 4-3092 FPS and shot 5 3099 FPS. Shot 1 and Shot 3 3.989" a part, this was the tightest shot group of the day but only by .013". This is why i started thinking about the powder burn rates effecting the stabilization of the bullet.

You need to fire at least 10 shot group to get a more accurate statistical analysis of your reload. Fire one shot every 5 minutes to give time for the barrel to cool off. Use a good chronograph.

Powder burn rate has no effect on bullet stability. The quality of the bullet and the uniformity of your barrel crown does. All bullet has wobble when it leaves the muzzle. Some bullet will travel quite a few distance before it stabilized itself. Bryan Litz explained it further in his article.

http://www.appliedballisticsllc.com/epswerve.html

 

[Oldtrader3]

Put a white sheet out in front of your muzzle and observe how much solid "ejecta" that you are propelling out at into the atmoshere with any particular powder, let alone how much gas is being spewed out at Mach 4, instantaneously at the muzzle. Most of it, even uncompletely burned powder granules, are lighter and faster than the slower Mach 2 to Mach 3 projectile itself. This despite (at that instant) being faster than the bullet, will not go far downrange. However, I always have wondered if these high speeds ejecta projectile particles and gases (at the moment of blowout from the muzzle) have some ability to destabilise the bullet base in flight?

Is this part of pitch and yaw effect with exterior ballistics? Not all of pitch and yaw may be due to unbalanced gyroscopic effect or is it only due to harmonic differences in barrel position? Who knows, it might make an interesting science project for someone with the high speed photography capability. There is "prior art" of existing high speed photography from ballistic labs. I wonder if engineers have tested these hypotheses?

Could this be why small powder charges in smaller rifle calibers tend to be more accurate than magnum cases with the same bullets, or is it a velocity to spin ratio effect (stability)?

 

[BalisticsNut]

I use a digital scale and in one of the shot groups, the FPS tested the same on two shots but those two shots were the furthest apart in the shot group. In four shots, shot 1 3102 FPS, shot 2-3077 FPS, Shot 3-3102 FPS, shot 4-3092 FPS and shot 5 3099 FPS. Shot 1 and Shot 3 3.989" a part, this was the tightest shot group of the day but only by .013". This is why i started thinking about the powder burn rates effecting the stabilization of the bullet.

You need to fire at least 10 shot group to get a more accurate statistical analysis of your reload. Fire one shot every 5 minutes to give time for the barrel to cool off. Use a good chronograph.

Powder burn rate has no effect on bullet stability. The quality of the bullet and the uniformity of your barrel crown does. All bullet has wobble when it leaves the muzzle. Some bullet will travel quite a few distance before it stabilized itself. Bryan Litz explained it further in his article.

http://www.appliedballisticsllc.com/epswerve.html

I hear ya on this one. I know my rifle and what it is capable of. I can put three through the same hole at 100 yards with one of my loads. This question was more about learning what will and will not cause bullet destabilization and what causes such a drastic difference between shots even though on paper they are identical in every shape and fashion.
To clarify, these shots were the last of 20 total shots fired over the course of an hour. The barrel was very warm to the touch but was not hot enough to make you jump.

 

[BalisticsNut]

Dubyam- THANKS! That was the most clarifying complete explanation I have heard to date. It makes me pause and wonder on how I can continue to improve on my testing processes. My only downfall in my testing that I can honestly state is that I do not weigh my brass and match brass weigts for testing. I do clean, prep, inspect and carefully weigh out every load. Its a pain in the arse but I do try and be consistant.

Thanks again for all the replies and explanations.

 

[atmoshpere]

BallisticNut,

If you haven't already read it, I think you would really enjoy "Rifle Accuracy Facts" by Harold R. Vaughn.

He tests alot of the things you are curious about and presents the results in his book. There are some great high speed photos of muzzle blast in millisecond increments from the time the bullet is still inside the barrel a few inches from the muzzle to the time it has left the influence of the blast.

atm

 

[Oldtrader3]

Vaugh's book is a classic but I found a copy for a reasonable price on EBay and bought. I will be interested to read what he has written.

 

[BalisticsNut]

Thanks for the recommendation. Ill have to pick that one up.

 

[Antelope_Sniper]

BN, just think of your barrel as a tuning fork. When you pull the trigger, the bullet strikes the botton of the tuning fork. Strike it just right, and you get a minimum of vibration, and a better group.

I tend toward slower powders, but not for the reason you quoted. I have sub moa load for my .338 using H4831, H4350, and H380.

Different powders tend to like differnet powders. Where you are having good luck with the stick powders, it makes me wonder if you are using a realitively cold primer. The RL powders might like something a little warmers.

 

[Ridge_Runner]

this is just my thoughts on harmonics, find a load with a powder that fills the case between 90 and 100% that reaches peak pressure after the bullets starts into the lands, and the harmonics will fix itself so to speak. at peak pressure the bullet is excellerating the way its intended if its started into the lands, then the bullet will exit at the same point in the barrels harmonic whip giving you much more consiistancy. alot of folks make it more complicated than it is. My opinion, worth what it cost ya, that and $1.16 will get ya a cup of java at about any 7-11
RR

 

[BalisticsNut]

Just a quick note. Thanks for all the responses. I did try a slower burning powder as I usually would and conducted a ladder test. Using the 90% fill method mentioned below for a starting point, I was able to achive 1.08" spread on my last three rounds. That would be IMR4350 42.5, 43.0 and 43.5 grains with Nosler 90 Gr BT pushing just at 3250FPS. I still need to refine that load but still was amazed by the performance with the slower burning powder with more pressure and how it increased the accuracy. I have a good understanding of the harmonics, thanks to all the explanation and PMs.