Transonic Cone Theory of Bullet Motion

[_Windrider_]

View attachment 7871534

Well there you go, I don’t have the litz books handy. I guess all that is left is to convert radians per second to rpm’s but I’m not convinced that’s the right formula and at a minimum doesn’t tell the whole story.

Also that white paper is for artillery and requires the installation of a sensor on the shell to measure the inertia. I’m not sure it applies to small arms projectiles at this time.

 

[Secant]

Well there you go, I don’t have the litz books handy. I guess all that is left is to convert radians per second to rpm’s but I’m not convinced that’s the right formula and at a minimum doesn’t tell the whole story.

Also that white paper is for artillery and requires the installation of a sensor on the shell to measure the inertia. I’m not sure it applies to small arms projectiles at this time.

Yep, for artillery. Physics isn't really going to vary from artillery to bullets from a big picture perspective, so I would expect an exponential rotational decay for bullets as well. Don't take this the wrong way, but unless you are able to write and solve the appropriate differential equations, I wouldn't worry about getting too far into the weeds. If you have the appropriate background in kinetics, kinematics, fluid mechanics, etc., then by all means, go nuts.

And for whatever it's worth, I 100% agree that projectiles are not course correcting mid-flight. I don't follow as to how the bullet's position relative to max ord plays any role. I see it as a time-of-flight issue. The greater the amount of time of unstable or less-stable flight corresponds to greater unpredictability/inconsistency.

 

[_Windrider_]

Yep, for artillery. Physics isn't really going to vary from artillery to bullets from a big picture perspective, so I would expect an exponential rotational decay for bullets as well. Don't take this the wrong way, but unless you are able to write and solve the appropriate differential equations, I wouldn't worry about getting too far into the weeds. If you have the appropriate background in kinetics, kinematics, fluid mechanics, etc., then by all means, go nuts.

And for whatever it's worth, I 100% agree that projectiles are not course correcting mid-flight. I don't follow as to how the bullet's position relative to max ord plays any role. I see it as a time-of-flight issue. The greater the amount of time of unstable or less-stable flight corresponds to greater unpredictability/inconsistency.

The max ord thing is just a thought. I’m not spouting it as fact or theory. I just think of it in terms of its pitch and yaw as it travels up before it begins to descend. There could very well have no basis in fact. I’m not a ballistician. But if it reaches transonic before it starts to come down you compound the effects defeating gravity with a now unstable projectile is it’s still trying to reach that ord before it descends I just think it’s worse than it happening when it hits that point when it’s already on it’s way down. It may act more “predictably” in that situation.

 

[Lowlight]

You can see it's off center


Once they start cavitating it's over, this was so predictable every video I shot was a success, I never missed a bullet coming apart

 

[timintx]

Ok still tracking …just going to chop it up a few times because there is a mix of testing and theory inside

Also, there will be a bunch of questions that may cross between theory and proprietary info, so answer what you can without “slipping”..dont want to cause trouble if you have other entities involved.

So previously you had seen 2 out of 10 “bullet trace” look different in flight but they were still in a tight group, but you didn’t have a reason/theory yet.


During testing for positive compensation:

From what I had always read positive compensation only really showed up at distance because the trajectory difference of velocity at 100 was almost impossible to separate from possible bullet irregularities and environmentals.

I know short range BR guys dont even weigh powder, they volume dump at the bench because velocity differences don’t really show up.

How did you induce the variables for the 100 yard testing, different charge, seating depths?

Were you able to compensate for those “standards”, and bring the POI inside/tight which is actually “outside” the expected groups from those different loads?

Im thinking if several loads expected POI partially overlap then its luck of the draw/ possible if they converge to the same POI even without compensation?


Modifying patterns..:

What or how much positive compensation had you been seeing at 100, or better yet what velocity differences were you using/ targeting as your variables (I would think the weapon, components, location, POA, etc are the static variables).

The suppressor was the right weight…:

That must be a formula; I have not seen a calculation for a tuner weight which in theory is what the suppressor is acting like…as you suggest it “should be tuned” or im off base?

I would think that calculation includes, barrel material, barrel length, bore size, OD, profile at a minimum.

Is the suppressor a clip on or a screw on?

If the suppressor should be of correct weight, you also must have calculated the exact position of the suppressor when attached as the exact location is part of setting up a tuner.

If the exact attachment point is calculated, was the suppressor able to be “moved” fore and aft for tuning?

I’d think with the tuners on the market that adjust/move a few .001”s when adjusting.. how was that accomplished or the suppressor was designed with best case scenario and load development was “going to bring it home”?


Downrange:

So, after the suppressor killed your dreams at 100 (lol) you shot it farther (1000) and the instead of the groups being 30” / 3MOA they were tac driving..with suppressor on correct?

Did you try the same ammo at 1k without suppressor for a quick base line of what the rifle and load could actually do?

Would be great to know if the load/rifle was capable of “clay bird” at 1k without suppressor, then we would know suppressors effect at 1k, if nothing else.


Final design:

You believe that by redesign you have made a “proper” suppressor which has limited effects on accuracy compared to the original un-suppressed rifle or that’s still on going


Sorry if long winded, trying to make it so I can follow your answers properly and not ask doubles.


Thanks

edit..ill check spelling AGAIN a little later..Iphone

May be best to answer these questions on another thread , I dont want to detract from the original post.

 

[Feniks Technologies]

Anyone have any theories how doppler radar isn’t able to pick up bullets spiraling with a wider radius and ending with a smaller?

 

[Sandow the Heretic]

Anyone have any theories how doppler radar isn’t able to pick up bullets spiraling with a wider radius and ending with a smaller?

They are powered by electricity and not unicorn farts?

-Alex

 

[Mike Casselton]

The term is laminar not laminate. And eventually it becomes a turbulent zone and that’s what creates the twist

What do you know? You just fly airplanes...

To add to this discussion, if you've ever watched an aircraft takeoff in high humidity conditions you can see the effects of laminar flow.

And yes, the flow can and will oscillate without the aircraft wobbling, corkscrewing or any other control issue.

So many people have little to zero understanding of wind effects on projectile flight.
Spend some time watching sensitive wind flags and how tiny changes affect point of impact and flight characteristics.

 

[_Windrider_]

What do you know? You just fly airplanes...

To add to this discussion, if you've ever watched an aircraft takeoff in high humidity conditions you can see the effects of laminar flow.

And yes, the flow can and will oscillate without the aircraft wobbling, corkscrewing or any other control issue.

So many people have little to zero understanding of wind effects on projectile flight.
Spend some time watching sensitive wind flags and how tiny changes affect point of impact and flight characteristics.

 

[_Windrider_]

Anyone have any theories how doppler radar isn’t able to pick up bullets spiraling with a wider radius and ending with a smaller?

because doppler doesnt detect rotation like that. it measures velocity as an object moves towards or away or in the case of weather detection, it can take a vertical cross section and detect wind speed and direction because its picking up on the particles in the air.

 

[Feniks Technologies]

because doppler doesnt detect rotation like that. it measures velocity as an object moves towards or away or in the case of weather detection, it can take a vertical cross section and detect wind speed and direction because its picking up on the particles in the air.

It wasn’t a serious question. Just making a point. Lol

 

[Jim Boatright]

View attachment 7871534

Just out of the muzzle, the initial spin-rate ω0 of the bullet in radians/second is given by:

ω0 = 2π*V0/Tw = 2π*12*V0/(n*d)
where V0 is the muzzle velocity in feet/second, the twist rate Tw is given in feet/turn, n is the number of calibers/turn, and d is the caliber in inches.

Thereafter, the spin-rate ω(t) of the bullet slowly decays almost exponentially with time of flight t (in seconds), so that

ω(t) ≈ ω0*exp[-(0.0321/d))*t]

where the caliber d is given in inches. This formulation was suggested by Dr Geoffrey Kolbe in England.

The numerical coefficient in the exponential (in units of inches per second) comes from analysis of PRODAS spin-rate data for several different 30-caliber military rifle bullets out to 900 yards. The exponential expression is about a 1-percent fit to the PRODAS aerodynamic data.

Doppler radar tracking of projectiles fired for maximum range DOES show the damped coning motion of spin-stabilized projectiles during the descending limb of their long-range flights. You can measure the remaining coning rates directly from the modulated velocity plots.

 

[Dogtown]

Dang, wish I knew how to drop Omega into a post like that?

 

[timintx]

Just out of the muzzle, the initial spin-rate ω0 of the bullet in radians/second is given by:

ω0 = 2π*V0/Tw = 2π*12*V0/(n*d)
where V0 is the muzzle velocity in feet/second, the twist rate Tw is given in feet/turn, n is the number of calibers/turn, and d is the caliber in inches.

Thereafter, the spin-rate ω(t) of the bullet slowly decays almost exponentially with time of flight t (in seconds), so that

ω(t) ≈ ω0*exp[-(0.0321/d))*t]

where the caliber d is given in inches. This formulation was suggested by Dr Geoffrey Kolbe in England.

The numerical coefficient in the exponential (in units of inches per second) comes from analysis of PRODAS spin-rate data for several different 30-caliber military rifle bullets out to 900 yards. The exponential expression is about a 1-percent fit to the PRODAS aerodynamic data.

Doppler radar tracking of projectiles fired for maximum range DOES show the damped coning motion of spin-stabilized projectiles during the descending limb of their long-range flights. You can measure the remaining coning rates directly from the modulated velocity plots.

Thank you Jim for clearing that up . This explains what I have seen in my testing.

 

[357Max]

Just out of the muzzle, the initial spin-rate ω0 of the bullet in radians/second is given by:

ω0 = 2π*V0/Tw = 2π*12*V0/(n*d)
where V0 is the muzzle velocity in feet/second, the twist rate Tw is given in feet/turn, n is the number of calibers/turn, and d is the caliber in inches.

Thereafter, the spin-rate ω(t) of the bullet slowly decays almost exponentially with time of flight t (in seconds), so that

ω(t) ≈ ω0*exp[-(0.0321/d))*t]

where the caliber d is given in inches. This formulation was suggested by Dr Geoffrey Kolbe in England.

The numerical coefficient in the exponential (in units of inches per second) comes from analysis of PRODAS spin-rate data for several different 30-caliber military rifle bullets out to 900 yards. The exponential expression is about a 1-percent fit to the PRODAS aerodynamic data.

Doppler radar tracking of projectiles fired for maximum range DOES show the damped coning motion of spin-stabilized projectiles during the descending limb of their long-range flights. You can measure the remaining coning rates directly from the modulated velocity plots.

Does this formula account for sectional density?
I’m no mathematician, but my instinct is telling me a long Mono will spin decay much quicker than a traditional lead core of same shape.

I’ve kicked around the idea that a jacketed Anviloy ® projectile could improve small caliber performance at ELR ranges. Of course this would be an AP round & wouldn’t play well with steel. Probably be fine at a mile+ with .224

 

[Jim Boatright]

Your feeling that that bullets having smaller axial inertia values would spin-decay faster is correct, Max, all else being equal. Where you are mistaken is in thinking this would be a large effect. The radius of gyration (kx) of a bullet about its spin-axis varies much more with caliber and overall "bullet" shape than it varies with any reasonable differences in non-homogeneous material densities. The axial moment of inertia (Ix) is given as m*(d*kx)^2, where m is the mass of the projectile and kx is given in calibers (d). "Depleted" uranium is the highest density core material available and makes the heaviest projectiles available in any given caliber. They no doubt have very long spin-decay time constants.

The formulation I gave is for existing military style jacketed, lead-alloy cored 30-caliber rifle bullets. Artillery projectiles, for example, all have much lower sectional densities than rifle bullets, but only slightly faster spin-decay rates reflected in their slightly smaller exponential time constants after adjusting for caliber difference.

 

[bulletbluesky]

These are typical experimental results for military 5.56 mm NATO round (M855 ,62 gr FMJ bullet).
Interesting, althought twist rate is obviously high enough to stabilise bullet quickly, after 400-500 m total angle of attack increases rapidly again. I didn't know how actually bad for M855 it is...

 

[timintx]

These are typical experimental results for military 5.56 mm NATO round (M855 ,62 gr FMJ bullet).
Interesting, althought twist rate is obviously high enough to stabilise bullet quickly, after 400-500 m total angle of attack increases rapidly again. I didn't know how actually bad for M855 it is...

That is so interesting , thank you . I wander if the larger variability at the muzzle were damped Mechanically, would that effect or improve the down range variability?

 

[bulletbluesky]

I wander if the larger variability at the muzzle were damped Mechanically, would that effect or improve the down range variability?

I doubt that.
Initial yaw & pitch angle, after projectile leaves the muzzle, is the subject of statistical dispersion from shot to shot.
Besides, the angles in tests can be artificially induced by putting plates close to the projectile's path along first few yards of a trajectory.
4°+ in this case is actually quite a lot (I think typical mean values are something around 2°?) but is probabably given to show given twist rate is adequate to damp out such oscillations completely after 150 m . M885 bullets are fired from M16A2 rifle with twist rate 1:7 in the tests. Between 150-450 m the yawing & pitching motion appears quite steady with angle of attack less than 1°, and after that it just increases.The question is what is going to happen after 800 m: is the 5.56 mm bullet going to exhibit slow-mode coning motion with some reasonable limit-cycle yaw property or is the slow-mode amplitude growth going to escalate further tremendously?
Anycase, owing to such behaviour maximum range of M885 ammunition fired from M16A2 is significantly less than 3600 m. That figure is probabaly just calculated and can be found on https://en.wikipedia.org/wiki/M16_rifle

 

[timintx]

I doubt that.
Initial yaw & pitch angle, after projectile leaves the muzzle, is the subject of statistical dispersion from shot to shot.
Besides, the angles in tests can be artificially induced by putting plates close to the projectile's path along first few yards of a trajectory.
4°+ in this case is actually quite a lot (I think typical mean values are something around 2°?) but is probabably given to show given twist rate is adequate to damp out such oscillations completely after 150 m . M885 bullets are fired from M16 rifle with twist rate 1:7 in the tests.
Between 150-450 m the yawing & pitching motion appears quite steady with angle of attack less than 1°, and after that it just increases.
The question is what is going to happen after 800 m: is the 5.56 mm bullet going to exhibit slow-mode coning motion with some reasonable limit-cycle yaw property or is the slow-mode amplitude growth going to escalate further tremendously?
Anycase, owing to such behaviour maximum range of M885 ammunition fired from M16 is significantly less than 3600 m. That figure is probabaly just calculated and can be found on https://en.wikipedia.org/wiki/M16_rifle
[/

I see . Thank you

 

[Milf Dots]

Don't hate me Frank lol but I have visually seen the bullets corkscrewing wildly a few times with fully qualified bullets and ultimately still hits within the group at longer ranges ,one example was at the 1000yd nationals when vapor trails were really showing up in detail , so much so that I could actually see the air spinning from the rifling on the bullet. 8 of the shots had a steady flow or v flowing smooth;y and then I saw 2 corkscrewing wildly out of ten shots . I just knew the 2 would be out of the group . They were not as the guy shot 4.5 Inch 10 shot group. From what I have seen the bullets are flying around the original flight path and comes in to it as the bullet settles down , I know these were still corkscrewing out to 800 yds or so from what I could tell, I have created it with some goofy baffling in my suppressors as well but lost no accuracy down range when it sucked at 100yds[3 inch group averages] . Then immediately go to 1000yds ,hit the clay pigeon dead center into 3 pieces and then with the next three shots hit all 3 pieces , These are not because of bad bullets but more of muzzle blast disturbances. I think this is what I think people are seeing but not knowing for sure without seeing the corkscrewing of Epicyclic swerve. but I can say I have visually seen the effect especially with funky baffling in my suppressors.

Tim in Tx

Our eyes lie to us regularly, ex: the woman at the bar who was hot last night, usually looks much worse in the morning.

 

[Dogtown]

It’s that damned Confirmation Bias…gets people every time.

 

[bulletbluesky]

I'd just add that the growth of the slow-mode amplitude, as shown above, begins before 450 m. The M885 has still velocity above 1500 ft/s there, which means the effect is not due to transonic zone vicinity, but transonic zone later can make things just worst downrange. What could be the cause of dynamic instability development? Maybe a nonlinear Magnus moment, maybe special construction of M855 bullet that presents difficulty in mantain structural and axial mass and shape symmetries?

 

[brianf]

It’s that damned Confirmation Bias…gets people every time.

Exactly. People still thinking 4 shots is the actual dispersion and yet magically the “non conforming” still reside in the overall group.

Almost like…hmmm 3 shots isn’t statistically significant…wonder where I heard that before

 

[timintx]

Our eyes lie to us regularly, ex: the woman at the bar who was hot last night, usually looks much worse in the morning.

I agree ,lol

 

[timintx]

I'd just add that the growth of the slow-mode amplitude, as shown above, begins before 450 m. The M885 has still velocity above 1500 ft/s there, which means the effect is not due to transonic zone vicinity, but transonic zone later can make things just worst downrange. What could be the cause of dynamic instability development? Maybe a nonlinear Magnus moment, maybe special construction of M855 bullet that presents difficulty in mantain structural and axial mass and shape symmetries?

The experiments I have done lately has been with known good quality bullets which does not mean much but by reducing any dispersion close to the muzzle definitely reduced it down range but as Jim Boatright mentioned it was much smaller than originally thought, in the case of a 190 SMK 30 cal has worked out to 1/10 of a MOA at 1000 yards . Sure was hoping for more of a improvement but as of now that’s all , but still testing though. It appears in my case anyway that the muzzle blast is a portion of the initial yaw at the muzzle and probably CG offset as well . I can only assume right now because more testing is needed but will stay at it .

 

[Dogtown]

Exactly. People still thinking 4 shots is the actual dispersion and yet magically the “non conforming” still reside in the overall group.

Almost like…hmmm 3 shots isn’t statistically significant…wonder where I heard that before

I feel like I’m constantly trying to explain to people why science is hard, and why a huge part of a science education is learning about natural human biases, and how to more accurately gather, process, and conclude trends from data.

But…but…feelings.

 

[JB.IC]

I feel like I’m constantly trying to explain to people why science is hard, and why a huge part of a science education is learning about natural human biases, and how to more accurately gather, process, and conclude trends from data.

But…but…feelings.

It’s much more enjoyable watching ignorance. I often want to help and then realize no one is going to compensate me for my three degrees/several years of education and research but they’ll expect me to condense all that information down to three sentences…. for free. Then want to see my data that costs a few thousand dollars… for free. Nah. I’m good. We have dweebs in the shooting community that can barely read but somehow make money reviewing reloading equipment. The world is a funny place.

 

[brianf]

It’s much more enjoyable watching ignorance. I often want to help and then realize no one is going to compensate me for my three degrees/several years of education and research but they’ll expect me to condense all that information down to three sentences…. for free. Then want to see my data that costs a few thousand dollars… for free. Nah. I’m good. We have dweebs in the shooting community that can barely read but somehow make money reviewing reloading equipment. The world is a funny place.

It’s only funny and possible because of social media/forums

20 years ago the same people did not have a platform to “spout their knowledge” because a magazine had journalistic standards to meet.

Now anyone can be self important as long as they have a screen name.

If 99% of what is posted in the hide had to be fact checked this website would be T&A pics and new build photos.

 

[bulletbluesky]

The experiments I have done lately has been with known good quality bullets which does not mean much but by reducing any dispersion close to the muzzle definitely reduced it down range but as Jim Boatright mentioned it was much smaller than originally thought, in the case of a 190 SMK 30 cal has worked out to 1/10 of a MOA at 1000 yards . Sure was hoping for more of a improvement but as of now that’s all , but still testing though. It appears in my case anyway that the muzzle blast is a portion of the initial yaw at the muzzle and probably CG offset as well . I can only assume right now because more testing is needed but will stay at it .

Use of yaw cards and different twist rates is an old but time consuming method. Surprisingly lot of experimental data one can derive without fancy and expensive equipment

 

[timintx]

Use of yaw cards and different twist rates is an old but time consuming method. Surprisingly lot of experimental data one can derive without fancy and expensive equipment

Yaw cards have worked extremely well but I can not help but wander is there is a deflection possibility. Years later I used velocity drop from muzzle to target and using groups at the same time to confirm suspected random dispersion . When the muzzle dispersion is highest so is the velocity loss . They both correspond well together to give a reasonable idea of bullet yaw amount at least from a comparative number .

 

[bulletbluesky]

Here is a classical paper about it:

https://apps.dtic.mil/sti/tr/pdf/ADA320953.pdf

 

[iceng]

Sorta what we are talking about, sorta not. Hes aussie, deal with it.

(Summary is you need lots of shots to get the rifle systems true spread, not a 3 or 5 shor group).

 

[timintx]

Sorta what we are talking about, sorta not. Hes aussie, deal with it.

(Summary is you need lots of shots to get the rifle systems true spread, not a 3 or 5 shor group).

I agree , I don’t think anyone including me would just use one or two groups as any proof of anything especially trying to determine dispersion. Why people keep saying that shooters just use one or two groups is beyond me . No one does that. There are many groups over many days over many weekends to confirm anything. I like to see a repeat of anything at least 10 times before I even start to believe , I think most shooters do as well . But measuring velocity drop from the muzzle to the target along with the groups just helps to confirm and reduce this bias and gives me an idea if this wobble is in fact reduced at least within a hundred yards. And for the record I have never ever said my guns are 1/4 MOA rifles , but I want to keep them as close as I can with what ever it takes to do so , no matter what anyone thinks . That is just my competitive nature I guess because I want that edge . Does not mean I will achieve it but I am gonna try anything and everything to better it and not just write it off as something I can not improve upon .

 

[bulletbluesky]

Positional "wooble" of trajectory for one particular shot of M885. This had reduced charge, hence lover muzzle velocity. Could such trajectory imprint be noticed by naked eye via vapor trail left behind, isn't clear to me (saw discussion on first page). Bigger initial yaw and bigger dispersion of it have some influence to precision however.

 

[timintx]

View attachment 8359405View attachment 8359414

View attachment 8359415
Positional "wooble" of trajectory for one particular shot of M885. This had reduced charge, hence lover muzzle velocity. Could such trajectory imprint be noticed by naked eye via vapor trail left behind, isn't clear to me (saw discussion on first page). Bigger initial yaw and bigger dispersion of it have some influence to precision however.

Going back to the first page I think as many have stated it looked worse than it really was , but what really threw me was that one minute there was a smooth laminar flow field and then there was not. I would like to know why if it was wind or the bullets which were fully qualified yet were different flight characteristics . There was a dark green background because we were shooting in the mountains and I was using Swarovski big eyes so the vapor trail clear as to detail.

 

[secondofangle2]

My contribution to cone theory is this:

When I take a shit, my turds exit the muzzle every which way, but when I flush it, the cone theory directs them all into a tiny little group as they go down range and out of sight

 

[bulletbluesky]

My contribution to this discussion is this:

When I take a shit, my turds exit the muzzle every which way, but when I flush it, the cone theory directs them all into a tiny little group as they go down range and out of sight

Well, that's an interesting observation. You should try to make your own theory based on that since "Cone Theory" proposed by OP is incorrect

 

[TripleBull]

I feel like I’m constantly trying to explain to people why science is hard, and why a huge part of a science education is learning about natural human biases, and how to more accurately gather, process, and conclude trends from data.

But…but…feelings.

I used to teach the scientific method to experienced scientists. They were required to take the course by their employer and most of them took it as an insult. I still study the topic and some of the most meaningful philosophy related to it is over 1000 years old. To be a great scientist, you must doubt yourself relentlessly and be the harshest critic of your work.

 

[secondofangle2]

Well, that's an interesting observation. You should try to make your own theory based on that since "Cone Theory" proposed by OP is incorrect

I’ll call it the turd theory of projectile motion and its equally valid as cone theory

 

[hero's machine]

It would seem that we could make this photographable by reducing the twist and velocity to where the transonic occurs shortly after the barrel. I have shot video of my 50 cal hawken shooting 460gr bullets and they can be seen yawing into the wind. That video was shot with my cellphone. I'd imagine with a better outfit it could be done.

 

[bulletbluesky]

It would seem that we could make this photographable by reducing the twist and velocity to where the transonic occurs shortly after the barrel. I have shot video of my 50 cal hawken shooting 460gr bullets and they can be seen yawing into the wind. That video was shot with my cellphone. I'd imagine with a better outfit it could be done.

That method, more or less sophisticated, has been extensively used at BRLs (combined tests - spark range + long range outdoors).
For 5.56x45 mm NATO ammo, SS109 and M855 projectiles, typical test conducted in 1980s yielded results looking like this:

Note that deep in the subsonic range (~Mach 0.7) some substantional total angles of attack for both projectiles exist indicating both projectiles can become dynamically stable even at ELR distances. However, total angles of attack like 6°+ increase total subsonic drag considerably in comparison with zero-yaw drags:

 

[hero's machine]

The 7 twist part makes me think there's potential for improvement on the test IF RPM decay is appreciable.

The velocity reduction is accomplished, but the rpm appears to be at full speed.

 

[bulletbluesky]

The 7 twist part makes me think there's potential for improvement on the test IF RPM decay is appreciable.

The velocity reduction is accomplished, but the rpm appears to be at full speed.

The scans are from "Aerodynamic and flight dynamic characteristics of the new family of 5.56mm NATO ammunition", Memorandum Report BRL-MR-3476, 1985. One of conclusions was that limit-cycle yaws in subsonic region, for both projectiles, exist.

They used accuracy barrels and their method is described as follows:

The results of a full 800 m range firings:

So, it seems that SS-109 was a somewhat better performer of the two. But it's more to the significant standard deviation than to the mere angle of attack, which makes that ammo inconsistent for use past 700-800 m range!

 

[hero's machine]

Much appreciate the reference material.

 

[bulletbluesky]

No problem. Properties of standard NATO ammo, especially 5.56 and 7.62 mm cal., have been researched/tested quite a lot in the past (interestingly, I couldn't find much about new M855A1 round in that respect, but I guess it's quite similar to SS-109). There is a ton of material one can find. Still, some things are not quite understood.
For instance:

But:

Obviously , this can't be satisfactory.
Certainly, 5.56 mm caliber with its' light weight projectiles is not known for its long range performance (not to mention ELR), but there are fine projectiles in that caliber too, that are clearly better in every aspect. Such one is little boy of snipping: