Hornady's tip melting findings

[sparker]

It is interesting that such convex drag curves are not seen in other tests of tipped bullets. One would think that the phenomenon would be present in multiple tests. Given the size, reputation and commitment of Hornady, I do not question their findings. It does raise many questions however.

If Mr.Tubb found the same issues with his tipped projectiles, then it represents another body of evidence to the tip melting problem.

I can hardly wait to read the explanations from people who are quite knowledgeable in this field. That said, utter silence would not surprise me.

 

[potatoe]

I'm wondering the same thing. I'm only doing a lot of assuming, but I guess its the same tip thats on the the A-maxs and probably the same tip that is on the V-max's. I wonder why the tip was melting on only this bullet. These new bullets aren't being shot out extreme velocities like a light V-max, and they aren't being shot out of a faster twist or higher velocity than the A-max's would in the same calibers that the new ELD's are.

I hope they put out more information, but then again I rarely get the heavy Hornady's to shoot so well that they are my go to bullet in anything so its not bothering me too much, but I really want to get those 87 vmaxs to work in something at long range!

 

[MasonInBend]

Hoping for Litz to chime in here....

I've been scratching my head trying to see what the "new" technology from Hornady's ELDs are. Plastic polymer tipped bullets for long range hunting have been around for a little while? I see Nosler's Accubond long range as being the exact same design but using the second generation partition tech.

http://www.nosler.com/accubond-long-range-bullet/

As I sit here and type this, I am looking at my box of Berger VLD's (complete with a quote from Regan) I'm about to load for my Creedmoor. I have to ask, are the VLDs with the bthp immune or resistant to the heat phenomenon?

On a side note, I am happy to see Hornady creating factory ammo that I can buy off the shelf for hunting at hopefully a more reasonable price than the competition.

 

[Bryan Litz Ballistics]

It's well established and understood that BC's are velocity dependent based on the comparison of a bullets drag to the standard model (G1, G7, etc). A bullet that's perfectly stable and not melting in flight will have it's G1 BC fall off as it slows down; that's just normal for all modern LR rifle bullets, not just those with plastic tips.

Also, there are numerous explanations to the observed convex drag curves. This paper (http://www.arl.army.mil/arlreports/2010/ARL-TR-5182.pdf) is a full aerodynamic work up the government did on the M855 round showing its dynamic instability, pitching/yawing, etc. In other words, some bullets fly with what's called 'limit cycle yaw', which is a coning motion that acts sort of like a trim angle to keep the bullet in equilibrium. Flying at a small coning angle adds drag which, depending on the damping exponents, can result in a convex drag profile. One aspect of bullet design that is known to have an effect on the magnitude of limit cycle yaw is boat tail design. Steep BT's tend to fly with larger limit cycle yaw, the 168 SMK being the most popular example of a bullet that exhibits dynamic instability at supersonic speed. The whole line of Nosler Ballistic Tips and Accubonds have steep BT's, as well as many of the Hornady Amax and Vmax line. The steep BT's on these bullets could cause convex drag curves.

The amount of limit cycle yaw a bullet has depends a lot on its gyroscopic stability, which is tied to twist rate. The Hornady paper doesn't say the barrel twist used for the testing. If, for example, the 7mm 175 Hornady and the 7mm 175 Nosler LRAB were both fired from the same twist barrel, it could just be a matter of the Nosler not getting fully stabilized and flying with larger limit cycle yaw angles which creates the convex drag curve etc. I've measured this very thing (higher drag and lower BC's from the muzzle) for bullets fired with marginal stability. The Nosler LRAB's in particular are longer bullets that require faster than standard twist to stabilize.

Another strange thing about the 'melting tip' theory and the convex drag curves is that the drag curves are shown to be convex beginning at the muzzle. They talk about the tips melting in flight, at long range, for heavy high BC bullets that maintain higher speed for longer flight (vs. a varmint bullet that slows down quickly). That makes sense, but then why are the drag curves convex beginning at the muzzle? It seems to take no time at all for the tips to 'melt' and affect the drag.

Setting aside the 'melting tips' theory for a moment; consider the positives.

Hornady has come out with a new line of high BC, heavy for caliber bullets which should be good for long range.

They are providing G7 BC's for these bullets. Based on Hornady's measurement of G7 BC's of some Berger bullets matching my measurements nearly identical, I'm guessing that the G7's Hornady is putting out for their new bullets are very accurate.

I'll continue exploring the melting tip theory vs. other theories that fit the data.

-Bryan

 

[Forum Boss]

^^ What he (Litz) said.

Having that kind of expertise here is one reason why this Forum is such a good place. Thanks Bryan for the important insights.

 

[jlow]

I have to admit that the very first time I heard of plastic tip bullets, I wonder about the tips melting. I had of course incorrectly assumed this was looked at but I was clearly wrong.

I guess one can always project what is happening using indirect Doppler radar information but as Brian pointed out, there are always other potential explanation.

Seems like knowing the shape of the bullet tip, the potential friction involved in the speed and duration of exposure, one could calculate the temperature experienced by the tips and knowing the melting point of the plastic tips, one could infer the likelihood of the tips melting.

The alternate supporting method would be direct visualization i.e. recovering fired bullets to look for melted tips, looking at what the tips do in a supersonic wind tunnel, or direct capture of images of the bullet tip with high speed cameras at extended distances.

All of this seems a bit obvious, I wonder if Hornady has done any of it.

 

[CharlieNC]

Perhaps melting is not the proper description, which suggests the polymer turns into a liquid like material. On the other hand a commonly used polymer like polypropylene undergoes softening at a warm room temperature, and at would not be a stretch to visualize this occuring. Chamber temps could easily lead to a malleable situation. Bout the marketing guys like more vivid terminology like melting.

 

[jlow]

I don’t think it makes any difference if we call it melting or softening, the key is whether it changes the shape of the tip and/or whether the tip is even retained as this can changes the configuration of the meplat and we all know that can change BC.

I am not saying I don’t believe that the tips can melt/soften but just pointing out that as with any scientific study, you have a lot more credibility if you can support your case with multiple lines of direct/indirect evidence.

 

[Berger.Fan222]

http://www.hornady.com/assets/files/resources/ELD-X_ELD-Match_Technical_Details.pdf

Figures 7 and 8 in Dave Emary's paper provide fairly convincing support for the hypothesis that bullet tips are deforming in flight. It is the simplest explanation for the observations of significantly reduced drag coefficients at higher temperatures. If factors other than temperature are held constant, a bullet is more stable at higher temperatures, so the lower drag coefficients do not seem to be explained by lower stability. The observation that the effect is much smaller for bullet tip material with a higher melting point also supports the hypothesis.

Dave Emary's paper does not seem to provide all of the data that Hornady has available to them, but those guys know what they are doing, and I would not expect them to draw the wrong conclusion due to confounding factors they failed to consider.

Perhaps evidence more convincing to the average long range shooter would be high speed video showing deformed bullet tips at long range or recovered bullet tips from shooting water or gelatin. There are some considerable technical challenges to either of these experiments.

We did observe some things with the Hornady AMAX in a long range contest on a very hot summer day a few years ago that suggested the plastic bullet tips were deforming in flight, but we did not have access to the fancy equipment Hornady has used to support their hypothesis. Kudos to Hornady for recognizing and fixing the problem.

 

[m500]

More links of interest.

http://www.hornady.com/support/heat-shield/#story

http://www.shotgunnews.com/news/hornady-heat-shield-more-than-just-hype/

 

[Keith Glasscock]

I guess I would take the following approach to this: If Hornady did side-by-side tests with both polymer tips, and the new material had a higher BC, then it can be surmised that the tip melt theory is at least somewhat correct.

Will the new tips fix all of the inflight increase in drag? I suspect not. There will always be something that we can do to improve the average effective BC that we obtain.

 

[jds holler]

Enter the age of ceramic tipped bullets. jd

 

[jlow]

I don’t want to be negative but before we give Hornady too much credit up front, it was the same company that manufacture of the original A-MAX and given the fact that the tips were plastic, they in fact did not test the possibility that there would be melting/deformation until years after.

In terms of how hard it would be to do these experiments, I doubt that the high speed camera idea is very difficult. What you need is a shooter who can hold reasonable accuracy at 1k (not hard to find), a high speed camera (these are available to those in the business), a way to protect the camera (steel plates), and way to trigger the camera (some sort infrared detector). I mean even semi-professional like the Myth Buster folks have been doing similar stuff?

 

[jds holler]

It was many years ago that I first saw high-speed pics of the lead tips melting off of bullets in flight. I don't remember details concerning velocity, distance, and such, but the pics were very vivid and interesting.

Lead melts in the 600's F zone, and I can't believe that they can't come up with something that won't beat that by a long shot. jd

 

[Berger.Fan222]

I don’t want to be negative but before we give Hornady too much credit up front, it was the same company that manufacture of the original A-MAX and given the fact that the tips were plastic, they in fact did not test the possibility that there would be melting/deformation until years after.

The same could be said of all companies that have made plastic tipped bullets. I give kudos to Hornady for being the first to recognize the problem and offer a solution.

This problem was much more challenging to find and fix than the general inaccuracy in BCs that most companies (except Nosler) have addressed in the past decade or so. Identifying the problem requires some combination of long range, high temperatures, high muzzle velocities, and precision drag measuring equipment.

Hornady has stepped up and taken a leadership role here, and I expect that the other companies offering plastic tipped bullets will soon offer their own solutions, now that the problem has been clearly identified.

 

[sparker]

I understand that there are issues that can cause dynamic instability that could yield convex drag curves. The issue as I see it is that Hornady produces convex drag curves for bullets that did not yield convex drag curves when tested by others. Why is there such an inconsistency that would invert the shape of the curve on multiple bullets tested by others?

Scott Parker

 

[jlow]

I don’t want to be negative but before we give Hornady too much credit up front, it was the same company that manufacture of the original A-MAX and given the fact that the tips were plastic, they in fact did not test the possibility that there would be melting/deformation until years after.

The same could be said of all companies that have made plastic tipped bullets. I give kudos to Hornady for being the first to recognize the problem and offer a solution.

This problem was much more challenging to find and fix than the general inaccuracy in BCs that most companies (except Nosler) have addressed in the past decade or so. Identifying the problem requires some combination of long range, high temperatures, high muzzle velocities, and precision drag measuring equipment.

Hornady has stepped up and taken a leadership role here, and I expect that the other companies offering plastic tipped bullets will soon offer their own solutions, now that the problem has been clearly identified.

I think both what we both stated is true. If the tips are truly melting, they made a mistake not figuring that out before hand, they are now releasing the info after finding out and of course, they are only doing it after they found a fix and using it to market their new product.

 

[garytex]

I'm following this with interest, as I have several thousand Hornady and Nosler .224 bullets in my prairie dog ammo components stash. My guess is the tips probably are melting on the bullet shot out of my .22 Hornet, but are they melting at 500 yards on the 223, or the 22 250? I suspect (hope) we will probably have observations from folks that will yield some some rules of thumb. I remember there was a pretty sharp old geezer (now don't take offense hey I think the old geezers are smart and I am becoming one myself). I believe his name was Merrill that was interested in and learned some things from capturing fired bullets. He built a long box of oiled sawdust that would capture bullets without deforming them. I wonder if that would work in this case? High-speed photography would be nice but is beyond the reach I think of most tinkerers.

 

[garytex]

Oops, correction I think the tips are NOT melting on the 22 hornet

 

[johnfred1965]

I've shot thousands of ballistic tips, v-maxs, and blitzkings, and melting or not, I don't think the prairie dogs ( or me for that matter) knew the difference. Just wondering if this is a solution looking for a problem.