Hornadys new 6mm 120g ATip

[urbanrifleman]

I get a laugh that their website calculator frequently contradicts what they print right on the box of bullets. The 85.5gn says 8-twist on the box, but their "stability" calculator says it is marginally stable, by a concerning amount and suggests 7-twist is needed for "full" stability.

View attachment 1803182
I don't know if they have actual Doppler data to back up these reported BC adjustments, or if it is calculated from the model alone.

EDIT: I just looked at the 80 VLD and it is even funnier. Their calculator predicts the BC is degraded almost to the level of the 75 VLD under the same shooting conditions shown above. In real life, the 80 VLD enjoys a considerable advantage over the 75 VLD. I am increasingly in agreement with you. It's not just conservative, it's actually misleading.

I have customers call me all the time quoting that thing. I need this much spin cuz the Berger thingy said so... It's only enough spin to blow up the bullet out of the barrel, but the thingy says you gotta have that...

Optimum spin is always optimum. Overspun is always overspun. There's no new bullet that's only going to shoot at terminal spin or above.

 

[round]

I get a laugh that their website calculator frequently contradicts what they print right on the box of bullets. The 85.5gn says 8-twist on the box, but their "stability" calculator says it is marginally stable, by a concerning amount and suggests 7-twist is needed for "full" stability.

View attachment 1803182
I don't know if they have actual Doppler data to back up these reported BC adjustments, or if it is calculated from the model alone.

EDIT: I just looked at the 80 VLD and it is even funnier. Their calculator predicts the BC is degraded almost to the level of the 75 VLD under the same shooting conditions shown above. In real life, the 80 VLD enjoys a considerable advantage over the 75 VLD. I am increasingly in agreement with you. It's not just conservative, it's actually misleading.

Mess around with the altitude and you'll see that if your a mile up, an 8tw would probably be fine.

 

[Evan]

Mess around with the altitude and you'll see that if your a mile up, an 8tw would probably be fine.

I am that high up and it does. In fact every 90gn bullet has stabilized from an 8 twist up here at moderate velocities and worked with no noticed loss of BC, but most of the US isn’t anywhere near this high an altitude. Anyone checking the box against the calculator will be confused about which to trust and err on the side of a faster twist. I can say that from personal experience. It continued right up until I spent $800 on a barrel and chamber that would blow up most every 90gn bullet I sent down it. To bring this back to the 120gn Berger and Hornady: I am really curious if 7 twist barrels will start to blow these things up as more and more people try it.

 

[ELR LVR]

Has that been an issue with the previous Atips?

For me, YES
7/10 dont reach the target
(Hornady's thin jackets)
When they do hit, they sure have a nice report though
---
for now, I don't think they are worth their asking price, Bergers hold up well enough

 

[kyotekiller25]

For me, YES
7/10 dont reach the target
(Hornady's thin jackets)
When they do hit, they sure have a nice report though
---
for now, I don't think they are worth their asking price, Bergers hold up well enough

I have to ask, if 7/10 aren't reaching the target, is that really a bullet failure or operator error? What bullet, twist, velocity are you having this issue may I ask?

I've shot thousands of ELDMs in 22/6mm/6.5/7mm/30 cal and have never had 1 blow up in flight. I also use them within their designed parameters. I stay well below 300K RPMs. More in the range of 240K-280K with 8 or 9 twists and a MV no greater than 3100.

Atips and ELDMs share the same jacket thickness, so the only way I can see you blowing up 7/10 bullets is pushing them well beyond their designated threshold for bullet RPMs, which is typically derived from shooting too fast MV with too fast of twist.

Berger also recommends staying at or below 300K RPMs as they also use thin jackets.

 

[ELR LVR]

I have to ask, if 7/10 aren't reaching the target, is that really a bullet failure or operator error? What bullet, twist, velocity is having this issue may I ask?

I've shot thousands of ELDMs in 22/6mm/6.5/7mm/30 cal and have never had 1 blow up in flight. I also use them within their designed parameters. I stay well below 300K RPMs. More in the range of 240K-280K with 8 or 9 twists and a MV no greater than 3100.

Atips and ELDMs share the same jacket thickness, so the only way I can see you blowing up 7/10 bullets is pushing them well beyond their designated threshold for bullet RPMs, which is typically derived from shooting too fast with too fast of twist.

Berger also recommends staying at or below 300K RPMs as they also use thin jackets.

Well, yes I am driving them fast
If you consider that operator error, then so be it
Yet Dtacs, Sierra's, Bergers dont do that.
So is it an operator issue or a bullet issue
Krieger 4 groove, 8 tw, 3200 fps
---
and forget about Amaxes (Eldm)
Every one shows a comet tail when going through paper
it just seems the Norm with Hornady's their jackets are approx .023" vs .030" thick

 

[kyotekiller25]

Well, yes I am driving them fast
If you consider that operator error, then so be it
Yet Dtacs, Sierra's, Bergers dont do that.
So is it an operator issue or a bullet issue
Krieger 4 groove, 8 tw, 3200 fps
---
and forget about Amaxes (Eldm)
Every one shows a comet tail when going through paper
it just seems the Norm with Hornady's their jackets are approx .023" vs .030" thick

I also only use 5R grooves which are easier on jackets then 3 or 4

I wouldn't necessarily call it operator error, but you're definitely on the ragged edge of things with a 4 groove, 8T, and 3200 fps.

 

[ELR LVR]

I agree a 5R should help, (but, when a 4 groove is in stock and 5R is 6 months wait.....)
it's just....why does Hornady have to cheap out on jacket thickness
when everyone else doesnt
I even have good luck with 112 Matchburners over Hornady's
So...what I mean to suggest is
---
If Hornady is the only one I have an issue with......(finish my sentence)
DTACS and Sierra MK's actually hold up to 3400 fps

 

[kyotekiller25]

I have customers call me all the time quoting that thing. I need this much spin cuz the Berger thingy said so... It's only enough spin to blow up the bullet out of the barrel, but the thingy says you gotta have that...

Optimum spin is always optimum. Overspun is always overspun. There's no new bullet that's only going to shoot at terminal spin or above.

I have found the stability factor for 22 cals in general just don't make a whole lot of sense. They are way way off. For example, 223 rem, 12 twist, 55g ballistic tip at 3200 fps gives a 1.1 SF....A 40g ballistic tip at 3800fps with same 12 twist shows 1.23 SF...Really?? Ok haha! I shoot the 75g ELDMs at 3000fps from a 28" 8 twist 223 and it only gives a 1.3 SF. They still shoot just fine for me out to 1K...I don't know if it has something to do with the plastic tips for their calculations, but that's insane to say a 40g at 3800fps in a 12 twist is "marginally" stable. Laughable at best.

 

[kyotekiller25]

I agree a 5R should help, (but, when a 4 groove is in stock and 5R is 6 months wait.....)
it's just....why does Hornady have to cheap out on jacket thickness
when everyone else doesnt
I even have good luck with 112 Matchburners over Hornady's
So...what I mean to suggest is
---
If Hornady is the only one I have an issue with......(finish my sentence)
DTACS and Sierra MK's actually hold up to 3400 fps

I believe Bergers and Sierras typically do hold up a little better to higher RPMs than Hornadys.

Since I really only shoot ELDMs, I make sure that when I build a rifle and want to shoot a certain weight of bullet, the muzzle velocity of said bullet and twist is the first thing on my mind, and that I don't want to be at that 300K threshhold. Also barrel heat and throat wear play a role also. So with a comp rifle where you're shooting 10-12 shot strings in 1-2 minutes, it's going to build up some heat and be harder on the jackets as well.

That's why I decided against a 240 WBY build with a 28" tube, 8 twist, shooting 108g ELDMs. Just didn't think it'd work to well. Maybe could've got by with a 9 twist, but I don't have that kind of money to chance or experiment.

 

[ELR LVR]

I believe Bergers and Sierras typically do hold up a little better to higher RPMs than Hornadys.

Since I really only shoot ELDMs, I make sure that when I build a rifle and want to shoot a certain weight of bullet, the muzzle velocity of said bullet and twist is the first thing on my mind, and that I don't want to be at that 300K threshhold. Also barrel heat and throat wear play a role also. So with a comp rifle where you're shooting 10-12 shot strings in 1-2 minutes, it's going to build up some heat and be harder on the jackets as well.

That's why I decided against a 240 WBY build with a 28" tube, 8 twist, shooting 108g ELDMs. Just didn't think it'd work to well. Maybe could've got by with a 9 twist, but I don't have that kind of money to chance or experiment.

Understood man,
I never really intended to shoot Hornady's much in a 6x284
And agree you should design the gun around the bullet you plan to shoot.
---
You must be in a different discipline
in F-Class we have 22 minutes to fire our string
I haven't engaged in the type of Comp you are referring to - is that PRS?
---
If I were gonna fire hot and heavy much - I would use something more like a 6 BR
15 record shots in 22 minutes, is mild on a gun.
So I like to use my hot rod
---
BTW, I use to use a 9 twist for 107 SMK's just fine - But then you're limited to 107's and lighter
Only reason I went 8 tw was to use 115 DTACs
As for my choice of using a 6x284, it's kinda like:
"you CAN compete with a 600 cc crotch rocket but....when there are 1 liter bikes, why would you want to?"

 

[kyotekiller25]

Understood man,
I never really intended to shoot Hornady's much in a 6x284
And agree you should design the gun around the bullet you plan to shoot.
---
You must be in a different discipline
in F-Class we have 22 minutes to fire our string
I haven't engaged in the type of Comp you are referring to - is that PRS?
---
If I were gonna fire hot and heavy much - I would use something more like a 6 BR
15 record shots in 22 minutes, is mild on a gun.
So I like to use my hot rod
---
BTW, I use to use a 9 twist for 107 SMK's just fine - But then you're limited to 107's and lighter
Only reason I went 8 tw was to use 115 DTACs

Yes, I am referring to PRS where we routinely shoot 10-12 shots in 90 seconds. I started with a 6 creed, 27" 8T sendero contour and 108g ELDMs at 3050fps. But, the barrel would still get pretty hot after about 7-8 rounds, and the barrel life on a 6 creed just isn't ideal for that type of shooting in my opinion. I'd rather not have to rebarrel every year anyway. I have since went to a 6 BRA, 26" 8T HV contour and 108g ELDMs at 2850fps. Much easier on barrels and it's just starting to get warm after 10-12 shots. My next barrel I plan to go 28" 7.5T just to add some weight/balance and see if I can get to the 2930-40 fps node a little easier than the 26" with the 105-108s. I also want to play with the 110g SMK some. So the 28" 7.5T should be about perfect with the 6 BRA and 108 eldms at 2940 or the 110 smks at 2850.

 

[ELR LVR]

Yes, I am referring to PRS where we routinely shoot 10-12 shots in 90 seconds. I started with a 6 creed, 27" 8T sendero contour and 108g ELDMs at 3050fps. But, the barrel would still get pretty hot after about 7-8 rounds, and the barrel life on a 6 creed just isn't ideal for that type of shooting in my opinion. I'd rather not have to rebarrel every year anyway. I have since went to a 6 BRA, 26" 8T HV contour and 108g ELDMs at 2850fps. Much easier on barrels and it's just starting to get warm after 10-12 shots. My next barrel I plan to go 28" 7.5T just to add some weight/balance and see if I can get to the 2930-40 fps node a little easier than the 26" with the 105-108s. I also want to play with the 110g SMK some. So the 28" 7.5T should be about perfect with the 6 BRA and 108 eldms at 2940 or the 110 smks at 2850.

Very cool
Yes I think anything under 3000 fps could go with a 7 or 7.5 twist barrel
I think you made a good choice in caliber for what you're doing there.

 

[BKA]

That's nuts. Those stability lines are insane. 3300 at 6.75 twist or it's not stable... Hmmm.

Go home Berger calculator, you're drunk.

I believe what you're missing about the graph is that lead core jacketed bullets in a 6.75 twist barrel are likely to blow up at approximately 2800 fps. Everything to the right of the red line is above the 300,00 RPM threshold and has a very high potential to come apart on the way to the target.

 

[284winner]

I've been shooting 80 eldm bullets for years at 315-325,000 rpms and never had one failure. I have heard of failures for sure but I don't think it's as much an RPM issue as it is a barrel twist one. Mines an 8 twist and the ones I've heard of failing were shot from a 7 twist and not even pushing the bullet as fast as I do. 325K RPMs in an 8 twist isn't causing the failures of 310K RPMs from a 7 twist from what I've seen

 

[davidjoe]

Question out of the clear blue. Where is the point of diminishing returns with bullet mass/length? Why not a 130 Gr 6mm bullet?

I don’t think the projectile is actually the limiting factor at the weight and length range we use, because a solid could always cure the RPM survival problem. (I have heard of 1 in 2 twist rates). As a matter of physics, the BC just keeps on increasing with bullet length.

It’s brass that fails first, (it all assumes a safe max PSI on the order of about 65k in most CF rifles) then barrel life would be the next weak link, and if a person was indeed willing to hammer their bolts with disposable thick steel cases, AND 200ish accurate rounds was acceptable (a battleship was 300) then the next link to fail at the status quo would be the typical actions and barrels.

Current custom oversize actions seem to be loafing, but experiencing 5 times the pressure and bolt thrust of present magnums to shoot a bullet with a G1 BC of 3.5 would destroy them, probably suddenly and unpredictably after seeming just fine.

Barrels of our diameters cannot handle those pressures, set aside wear. We have already seen that even at 1.25” a hidden defect in steel can result in an X in one shot and multiple pieces of flying steel in the next, with today’s rounds.

But scores are the real measure of the practical limit. Even if we don’t blow one up, the highest BC loads presently possible typically score lower in the second “half” of however many shots you’re taking than the first. Only barrel heat can really explain this phenomenon. Barrels just don’t shoot as well extremely hot.

I don’t think we are simply fatigued, bored or already disappointed, as explaining typical second half drop offs, because diminishing accuracy is a non-issue in .22 Benchrest, as barrel heat is a nonissue, and it is nearly imperceptible in the very moderate end of CF loads.

In F-Class, if your rifle can be picked up when finished mid barrel, and held and then carried there, after shooting, then accuracy by F-Class standards hasn’t fallen off yet by reason of heat. If you can’t take even the first step, there is a high chance the first ten shots scored better than the second ten.

 

[ELR LVR]

Question out of the clear blue. Where is the point of diminishing returns with bullet mass/length? Why not a 130 Gr 6mm bullet?

It's not so much the weight
but the length that gets you
---
We dont really want it heavier, (130 gr) but it would get heavier as the length went out longer.
So a bullet could be designed, so as to still weigh 115/120 grns, but be longer
since BC is more dependent on length than any weight
Plastic tips for instance are doing this for us
this is why we need a tighter twist to stabilize say a 69 TMK vs a 69 SMK
Make the plastic tip a needle....1 inch long....and you got yourself something like a 1.1 G1 BC/6mm
(just speculating there)
BUT heres the catch....the overturning moment of that bullet is higher, the center of pressure is more forward of the center of gravity, and has more leverage to overturn the bullet in flight
So by nature of those physics happening, needs a higher gyroscopic stabilizer force to counteract it.
And then we run into the problem I have
----
I drive them as fast as they can possibly go, just shy of blowing up
dependent upon my twist rate.
if I went tighter twist, I could not drive the current heavy pills to 3200
I would have to slow the load down for the bullet to survive
So if I upped the BC ....but had to slow the bullet down to stay within the laws of physics...
I am diminishing my outcome, slow it down means I need more elevation, wind has more time to affect the bullet while in flight etc.
I like: decreasing the amount of time the wind has to affect the bullet.
Elevation is easy, it is always the same. Wind....not so much.
So the least amount of time to target means the least amount of time wind has to influence bullet.
Which means, sometimes a lower BC bullet that you can drive faster to spend less time in the wind....will produce better results than a high BC slower bullet. Thats the fine line you have to run the numbers on.
----
There is the point of diminishing returns
The highest BC you can possibly drive the fastest speed...before failure
if you suddenly have to compromise one or the other....you are moving backwards again
(Kind of like the 7mm 180gr vs 195 gr Debate) Depending on the cartridge pushing it of course
---
But lets say a .284 Win....by going to the High BC 195, it may be slowing down 200 fps more than the 180 gr, and thereby allowing the wind more time to influence.
So you upped BC there, but it didn't do you any real good. (just an example)

 

[Tangent]

I'm thinking all those factors should be able to be converted into a formula allowing the calculation of the sweet spot.

 

[cranky]

The twist rate and rpm directly relate to gyroscopic stability. Too much spin and the centerline of the bullet does not follow the flight path, which increases dispersion from spin drift and asymmetric lift as the centerline deviates from the ballistic arc. That also reduces the BC, it magnifies the problem at higher SG- So the sweet spot really is a SG of 1.5, where the bullet is stable but not overstabilized.

 

[ELR LVR]

I'm thinking all those factors should be able to be converted into a formula allowing the calculation of the sweet spot.

An Efficiency index of sorts
That's a wonderful thought
Lots of math though.
I find it quicker to just run the numbers on Drop Charts and compare them.
Maybe 5 minutes.
Vs:

We could start with an initial Efficiency Number:

S = BC *Vo ^1.5
-------------------
W

and move on to Case capacity constraints

Vo ≈ k * √(C/W)

and end with your Sweet Spot:

S ≈ k^1.5 * (BC * C ^ 0.75
------------------
W ^ 1.75

it's like manually running the quickload math long hand
vs:
Simply looking at a loading manual and using drop charts and comparing 2 bullets
---
If I run the numbers using the formulas shown for a 60 grn water capacity Cartridge
comparing a 107 SMK with G7 BC of .262
to
Berger 120 LRHT with G7 BC of .328
We get an Efficiency score of (S) =
SMK 107 = 464.2
Berg 120 = 471.8
Showing the Berger 120 beats out a 107 SMK by a hair, in windage at all ranges
while the Berger is still going 150 fps slower than the SMK.
---
the berger only beats it out by 7 points or roughly 1.5 percent, this is a small margin,
A 1.5% margin is incredibly tight, and you are hitting on a major limitation of using a simplified algebraic formula to predict ballistic fluid dynamics.
The elevation difference at 1000 yds is minimal at a mere 0.6 MOA
However:
The higher the cross wind speed- the more the Berger beats out the SMK

---
However what this DOES NOT SHOW, is that the 107 will have a brief advantage at first using less elevation drop at short ranges due to the superior speed it leaves the barrel using the same case.
Another reason to compare drop charts, for the specific yardage you plan to shoot vs just using a simple set of formulas.