Hornady's tip melting findings

[loteksw]

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

Let me just add, does it make a difference based on bullet performance. from the few reviews I've read. Match grade ammo shoots a slightly smaller moa than ballistic tipped hunting ammo. 1/2 moa is about the same for tight groups of many brands. It would seem to me that if tips are melting it would effect point of impact. Yet many sub moa patterns are reported with accubond etc.

 

[Ggmac]

Sub MOA PATTERNS ? what we're talking shotguns all of a sudden

 

[ab_bentley]

2015 thread......

 

[284winner]

I wonder if the have any plans to do the smaller calibers particularly the 80GRN AMAX ?

I have some 80 eld-m bullets. They came out a while ago

 

[284winner]

Let me say this as I said in another thread regarding the Hornady Amax tips. I shot some 140 Amax bullets out to 1000 yards and into items such as sand hills and water jugs out to 650. The water jug penetration had sand behind it for bullet recovery. Out of all the bullets recovered, none were melted to my observation. I shot some 162s also with no signs of melting at 800 yards. Most of the bullets tips were destroyed beyond recovery but those that survived didn't look too bad but we're not melted. Unless the range that the tips melt at is beyond 1000 yards, I do not see any tip melting personally. Also bullet recovery from animals shows no melting as well. Although most bullets recovered from game had no tips and only fragments of copper and lead.

 

[Grimstod]

I have always suspected that the ELD stuff was crap.

 

[284winner]

I have always suspected that the ELD stuff was crap.

Me too. Especially when I watched the video. The tips are a different color but when I pulled them apart, they again seem to be of the same material. I'm going to do some heating of both tips equally and see if one is any more resistant than the other.

 

[loteksw]

Sub MOA PATTERNS ? what we're talking shotguns all of a sudden

Duh. Lets talk semantics. A 3/5/10 shot group produces a repeatable pattern if the conditions remain constant. A melting tip would be a variable.

 

[CharlieNC]

The term melting is not a good description, softening and deforming would be better. Friends who have a commercial long range steel setup say in the past they never recovered any Amax tips, but immediately began finding the new Eld tips. Anectodely there is a difference in durability for what its worth.

 

[Ggmac]

Most would call it data . Every time I hear , patterns or keyhole in firearms discussions I think shotguns and unstable bullets . Not groups , data , or shots that are on top of each other .