Any research available on launch dynamics of a bullet being altered by gun powder selection?

[Titan]

Does anyone know if there is any published research on the drag coefficient of a bullet being altered by different gun powder as suggested in this article linked below. Any sources on this phenomenon would be great. Or if any of the muzzle brake data on yaw limit has a secondary source. Thanks.

https://precisionrifleblog.com/2019/06/30/personalized-drag-models-the-final-frontier-in-ballistics/

 

[Ballisticboy]

While testing military bullets and weapons we would often see larger variations in the measured Cd from the same bullets fired from the same rifle than is present on those graphs. I am not saying there is no variation of bullet drag with the variables discussed but, when the variation you are looking for is smaller than the random variability from bullet to bullet, great care needs to be taken when drawing conclusions.

Doppler radar is not the only way for researching bullet behaviour like this. Flight Follower systems have been used successfully on bullets and a system known as MRDR can also be used. These two systems can only give data over a short range but the data is much more detailed than a simple drag curve. Spark ranges used to be used but, due to the minimum distances between spark stations, they are not so useful on small arms which have much shorter yaw wave lengths than large calibre calibres meaning a lot can happen between spark stations.

However, it is well known and has been for many years, that changing anything in the gun/charge/projectile/gun support system can and will change the drag on the projectile. In the gun support system I am including the shooter. Unfortunately most of the research is funded by the military and is thus classified and certainly all the data I am aware of is classified. Sorry.

 

[JPeelen]

In France it was found that the barrel design may have a very measurable effect.
A 7.62 mm 168 gr Match bullet was measured with radar, being fired from an "ordinary" barrel with 305 mm twist and another weapon using a tighter bore diamenter with deeper grooves and a 280 mm twist.
Above Mach 1.4 and below Mach 0.7 the measured drag coefficients (10 shots each) were practically identical.
But in the transonic region, bullets from the tighter barrel with the faster twist showed a 2 to 3 times larger drag coefficient variation from shot to shot, compared to the ordinary barrel.
While this does not asnwer the propellant question, it shows we are dealing with a lot of interacting factors determining drag.

 

[46and2]

Wow, I just read too much physics today.
Soooo... once I get my personalized drag model I'll have to do it all again when changing bullet lots.

 

[JPeelen]

Titan,
having read the arcticle you linked, I think it is a little over-optimistic in drawing conclusions from extremely small samples. For example, firing one shot per propellant charge, in my view is not a base on which to draw any conclusions. Before one starts to compare charges, it is necessary to establish the shot-to-shot drag variation within identical charges.

 

[Titan]

Titan,
having read the arcticle you linked, I think it is a little over-optimistic in drawing conclusions from extremely small samples. For example, firing one shot per propellant charge, in my view is not a base on which to draw any conclusions. Before one starts to compare charges, it is necessary to establish the shot-to-shot drag variation within identical charges.

I have a lot of questions about the article and it's methods as I have not heard much about muzzle pressure variance from powder selection and yaw limit cycle. To answer one of my original questions I found an article on silencers and yaw limit and coefficient of drag by
Elya Courtney
, Roy Couvillion
, Amy Courtney
, and Michael Courtney
link is below:
https://arxiv.org/pdf/1802.05748&ve...FjAAegQIAhAB&usg=AOvVaw3Bc50xogiMBjwFZjuyrngz

 

[dcali]

I have a lot of questions about the article and it's methods as I have not heard much about muzzle pressure variance from powder selection and yaw limit cycle. To answer one of my original questions I found an article on silencers and yaw limit and coefficient of drag by
Elya Courtney
, Roy Couvillion
, Amy Courtney
, and Michael Courtney
link is below:
https://arxiv.org/pdf/1802.05748&ve...FjAAegQIAhAB&usg=AOvVaw3Bc50xogiMBjwFZjuyrngz

In my opinion, this paper is silly. You can't do what he does with a labradar and expect it to be meaningful. Like much of Courtney stuff, it sounds "sciencey", but it's just some dude at a range using inadequate instruments trying to measure stuff.

 

[dcali]

This obsession with drag is getting out of hand. There is only so much you can calculate before it gets meaningless, and we're well past that point for our purposes. The article doesn't discuss uncertainty, except to say that it's unknown. That is the one thing that needs to be known to evaluate those charts!

Observations about these equipment related factors are interesting, but not very useful. For example, the powder chart uses different velocities. That's not a good experiment. It's just collecting data for the sake of it. It's almost like we discovered (relatively) cheap radars, and now use it to measure everything. When you've got a hammer, everything is a nail.

To put all this in context, run a calculation on a bullet using a G1 and G7 BC out to 1000 yards. Those are dramatically different drag curves. The difference in results is very small. When you start getting into drag curves that are essentially the same within the limits of uncertainty, you're done. It's time to solve a different problem.

But what about ELR and transonic, you say? I say the wind is by far the greater uncertainty, to the point where it swallows up any drag variation attributable to these factors. The largest error always dominates, and in this case, it's huge.

I'm all for measuring and exploring, but we have to be very careful about drawing conclusions from stuff like this. You don't need a personalized drag curve.

 

[Titan]

This obsession with drag is getting out of hand. There is only so much you can calculate before it gets meaningless, and we're well past that point for our purposes. The article doesn't discuss uncertainty, except to say that it's unknown. That is the one thing that needs to be known to evaluate those charts!

Observations about these equipment related factors are interesting, but not very useful. For example, the powder chart uses different velocities. That's not a good experiment. It's just collecting data for the sake of it. It's almost like we discovered (relatively) cheap radars, and now use it to measure everything. When you've got a hammer, everything is a nail.

To put all this in context, run a calculation on a bullet using a G1 and G7 BC out to 1000 yards. Those are dramatically different drag curves. The difference in results is very small. When you start getting into drag curves that are essentially the same within the limits of uncertainty, you're done. It's time to solve a different problem.

But what about ELR and transonic, you say? I say the wind is by far the greater uncertainty, to the point where it swallows up any drag variation attributable to these factors. The largest error always dominates, and in this case, it's huge.

I'm all for measuring and exploring, but we have to be very careful about drawing conclusions from stuff like this. You don't need a personalized drag curve.

While I appreciate the input on the credibility of the articles linked, I am just looking for any sources that make reference to the claimed phenomenon linking muzzle pressure to yaw limit cycle, like you I found many of the claims unsupported and I had never heard of anyone linking muzzle pressure to drag or behavior of the bullet at launch and I wanted to see if this road had been traveled down and documented by better scientists. The only stuff i have found has been on artillery field guns and uneven muzzle pressure imparting yaw, a lot of stuff on "fleet yaw" and terminal short range performance of the M855 from the early 2000s.

 

[dcali]

While I appreciate the input on the credibility of the articles linked, I am just looking for any sources that make reference to the claimed phenomenon linking muzzle pressure to yaw limit cycle, like you I found many of the claims unsupported and I had never heard of anyone linking muzzle pressure to drag or behavior of the bullet at launch and I wanted to see if this road had been traveled down and documented by better scientists. The only stuff i have found has been on artillery field guns and uneven muzzle pressure imparting yaw, a lot of stuff on "fleet yaw" and terminal short range performance of the M855 from the early 2000s.

I've not heard this claim about the yaw limit cycle. The yaw limit cycle doesn't begin (if it exists) until way down range. I don't know enough about the causes to say it can't be impacted by launch conditions, but I've always been under the impression that it's more a matter of bullet geometry and spin - basically a function of the Magnus moment.

 

[243winxb]

https://discover.dtic.mil/results/?q=muzzle pressure to yaw limit cycle, l

Search the government tests.

 

[Titan]

https://discover.dtic.mil/results/?q=muzzle pressure to yaw limit cycle, l

Search the government tests.

Thanks for the link!

 

[Don_Parsons]

Test drag at your shooting range using your own rifle and keep notes of what the boolitz are doing...

Your rifle,,, your cartridge,,, your intended boolit,,, your case and primer along with the powder you use...

Life is just that simple if a person chooses it...

To much math and science to get in the way of my shooting sports,,, I only shoot close range stuff in the 100 to 1700 metres,,, whoops I mean 2200 meters now that my new custom is built... LOL

Yuppers,,, I'll let others do the nasty stuff as I spend my days hunting,,, plinking and short range to out and beyond what the majority of shooters only dream about...

Lifes to short to get hung up in the tech stuff,,, wizer for me to know what my unit is doing with the materials I have to get things done...

 

[Ballisticboy]

While I appreciate the input on the credibility of the articles linked, I am just looking for any sources that make reference to the claimed phenomenon linking muzzle pressure to yaw limit cycle, like you I found many of the claims unsupported and I had never heard of anyone linking muzzle pressure to drag or behavior of the bullet at launch and I wanted to see if this road had been traveled down and documented by better scientists. The only stuff i have found has been on artillery field guns and uneven muzzle pressure imparting yaw, a lot of stuff on "fleet yaw" and terminal short range performance of the M855 from the early 2000s.

As said by damoncali there should not be a direct link between muzzle pressure and yaw limit cycle. Muzzle pressure will be just one of the many parameters affecting the initial yaw and yaw rate imparted onto the bullet in the intermediate ballistic area, all of which should damp out in a dynamically stable bullet long before getting to the yaw limit cycle. The variations in initial yaw will give variations in drag but if you would see any difference over 600 or even 2200 metres is debatable considering all the other error sources. On the subject of short range terminal effects, yaw is actually beneficial by increasing the terminal effect unless you are trying to penetrate barriers.

The problem with bullets is that on some designs the dynamic stability is marginal. I have seen test results where the same bullet models fired from the same guns and tracked using flight follower cameras varied between dynamically stable with reducing yaw to neutral dynamic stability where the bullet yaw remained unchanged. In these cases there would be a difference in drag between bullets over a longer range which may lead to conclusions on yaw limit cycle which are not strictly accurate though it is debatable.

Personally I really wouldn't worry about it since there are plenty of other error sources which will have a much bigger effect.

 

[BronzeArcher]

I don't think the skepticism of using a LabRadar to measure short range drag (50-100 yards) is justified. With due care, results are usually in good agreement with reliable sources. Having tried it myself, measurements seem adequate to assess tip off and short range yaw behavior that gives comparable results to using yaw cards. But the LabRadar is so much easier to set up and use than yaw cards.

But on the whole, I agree that this discussion is pretty far off into the weeds and likely without application for most PRS or ELR shooters. But if someone does want to investigate if some factor is impacting their launch dynamics, a LabRadar may be a reasonable tool for the job. Confidence would be higher of one used yaw cards also, at least until they gained confidence that the LabRadar was adequate and being used correctly for the task.

 

[243Mendoza]

...I had never heard of anyone linking muzzle pressure to drag or behavior of the bullet at launch and I wanted to see if this road had been traveled down and documented by better scientists. ...

Checkout Chap 7 of "Rifle Accuracy Facts" by Harold Vaughn who was a supervisor of the
Aeroballistics Division at Sandia Labs.

 

[Ballisticboy]

I don't think the skepticism of using a LabRadar to measure short range drag (50-100 yards) is justified. With due care, results are usually in good agreement with reliable sources. Having tried it myself, measurements seem adequate to assess tip off and short range yaw behavior that gives comparable results to using yaw cards. But the LabRadar is so much easier to set up and use than yaw cards.

The problems I have found using fixed head doppler radars like the LabRadar is that the output you see is driven by the curve fit algorythm/filtering used in the radar to produce the "measured" velocities. The shape of the drag curve obtained from analysis of the radar data is created by whatever algorythm/filtering is used, not the true measured data and often leads to unrealistic drag curves being obtained. This is one thing I have noticed when analysing LabRadar produced detailed data.

This is why we never used fixed head radars unless we could get to the absolute raw data to apply our own methods for data filtering. I do not believe this is possible on the LabRadar since even the detailed time/velocity/range data I have seen displayed considerable evidence of data curve fitting/filtering.

 

[dcali]

I don't think the skepticism of using a LabRadar to measure short range drag (50-100 yards) is justified. With due care, results are usually in good agreement with reliable sources. Having tried it myself, measurements seem adequate to assess tip off and short range yaw behavior that gives comparable results to using yaw cards. But the LabRadar is so much easier to set up and use than yaw cards.

But on the whole, I agree that this discussion is pretty far off into the weeds and likely without application for most PRS or ELR shooters. But if someone does want to investigate if some factor is impacting their launch dynamics, a LabRadar may be a reasonable tool for the job. Confidence would be higher of one used yaw cards also, at least until they gained confidence that the LabRadar was adequate and being used correctly for the task.

I've used a labradar to measure BCs. It works surprisingly well given the obvious limitations - or at the very least, it does a good job with some bullets at matching published data. It's not something I would count on, except with a great deal of caution.

But Courtney goes a bit further than this and way oversteps the limits of his equipment. From his self-cited paper on measuring yaw with chronographs:

"Since the drag coefficients will decrease as pitch and yaw are damped, the theory of bullets going to sleep (pitch and yaw damping) predicts that the drag coefficients for the near 50 yard interval will tend to be above the curve and the drag coefficients for the far 50 yard interval will tend to be below the curve."

This is not real science. It's shooting lore masked with buzzwords.

 

[BronzeArcher]

Not sure how all the above rabbit trails relate to the question at hand.

With careful alignment to maximize signal to noise ratio, the LabRadar unit often produces accurate and repeatable results. One can download the raw velocity vs. distance data, perform a linear fit, and obtain a slope with an uncertainty less than 1% for data out to 50 yards where the signal to noise is very good. This slope is closely related to the drag coefficient for the velocity measured, such that the uncertainty in those drag coefficients can also be less than 1%. Further, one can also fire 5-10 shots and will often see that shot-to-shot drag coefficients also vary by less than 1%.

Suppose this is the case for a given bullet of interest. Now, one can change an experimental variable of interest. Suppose one changes the powder from H4350 to H4831, keeping the muzzle velocity and all the other factors constant. If the second powder also yields uncertainties in the drag less than 1%, but the mean drag is 4% higher than the first powder, I would venture to say that one has provided experimental support for the hypothesis that the launch dynamics were altered by the gun powder selection. Now, this support would be stronger if accompanied by yaw card data showing one powder had a mean max tip off angle of 4 degrees, while the other powder had a mean max tip off angle of 2 degrees.

 

[Ballisticboy]

With careful alignment to maximize signal to noise ratio, the LabRadar unit often produces accurate and repeatable results. One can download the raw velocity vs. distance data, perform a linear fit, and obtain a slope with an uncertainty less than 1% for data out to 50 yards where the signal to noise is very good. This slope is closely related to the drag coefficient for the velocity measured, such that the uncertainty in those drag coefficients can also be less than 1%. Further, one can also fire 5-10 shots and will often see that shot-to-shot drag coefficients also vary by less than 1%.

A couple of points.
Distance cannot be raw data since a doppler radar does not measure distance, it has to be derived from the velocity time data. Even the velocity data which I have been supplied in the past as "raw" data from a LabRadar was obviously not true raw data being too clean and not the correct shape at the very start of the measurements. True doppler radar raw data starts off with a few low values which climb up to the true velocity measurements as the bullet moves away from the gun and properly into the radar beam.
Secondly a linear fit is certainly not the correct fit to put to the data particularly just after the bullet leaves the barrel and will not produce the correct drag curve shape if analysed correctly. The most realistic curve fit shape I have found is normally a fourth order equation.
Where I would agree is that the radar needs careful alignment.