Is there actually any downrange advantage for very heavy for caliber bullets?

[tim_w]

A bullet with incredibly long bearing surface and one of the heaviest in class with also a super high bc is the 223 95gr SMK. It's got a relatively short nose average bt but a body so long compared to the 90gr berger it needs 2x the freebore of a bullet only 5 gr heavier and could even use more. Its also will shoot incredibly small groups but the long bearing surface does hurt the velressure ratiio potential. The BC has been confirmed by numerous FTR shooters out to 1k out of the lowly 223.

Then you have bullets with equally incredibly short bearing surfaces for their weight such as the 338 250 EH. Yet even with this very short surface it's quite forgiving to tune has great terminal performance and can achieve some of the fastest vel for weight of any of the 338.

 

[dfanonymous]

Bullets with a very long bearing surface, such as the Corbin style that I am referring to (I learned the name of this style thanks to this thread), can't possibly have nearly as high of a ballistic coefficient as a VLD style bullet of the same shape. .25 cal VLD style bullets of 145, 163 and 180 grains would have rifling twists required for stabilization that I'm guessing could induce excessive rotational stress on the bullet when driven to velocities that would allow the bullet to outperform the 135 grain VLD in terms of drop and drift. I could definitely be wrong on this, but I would love to see a side by side comparison of both style bullets driven to maximum velocity potential (I'm talking normally accepted peak pressures). Actual shooting, not estimated BC.

Bingo.
If they made the heavy weights in VLD style, then I can believe they would outperform lighter VLD style bullets. I just have a hard time believing a somewhat heavier Corbin style bullet (a term I learned thanks to this thread) can outperform a somewhat lighter VLD style bullet in terms of drop and drift, assuming both bullets are launched to the same velocity potential from a given cartridge.

The ELD has longer bearing surfaces. Longer than the VLD in my finding across most calibers I work with. It has a high BC and is one of the most independently tested bullets out there. Litz/AB team has data on it. I don't use BC, but rather a custom curve, but inside supersonic, is very close to published mach data by hornady. Keeping in mind variances in rifles vs testing barrels.

For PRS I have pushed bullets like the 6GT to dust before, keeping at max velocity, within the rules. So, yeah, you have to worry about that. I think even more when running monos.

 

[FEENIX]

Bullets with a very long bearing surface, such as the Corbin style that I am referring to (I learned the name of this style thanks to this thread), can't possibly have nearly as high of a ballistic coefficient as a VLD style bullet of the same shape. .25 cal VLD style bullets of 145, 163 and 180 grains would have rifling twists required for stabilization that I'm guessing could induce excessive rotational stress on the bullet when driven to velocities that would allow the bullet to outperform the 135 grain VLD in terms of drop and drift. I could definitely be wrong on this, but I would love to see a side by side comparison of both style bullets driven to maximum velocity potential (I'm talking normally accepted peak pressures). Actual shooting, not estimated BC.

This is why neither @Bghunter338 nor I will give a ballpark BC (while I am a big fan of BC, there are other attributes of the bullet that I am more interested in now) on the 145s and 163s. We are pressure testing with different powders and sharing information at our own pace. If someone could do better than us, by all means, he/they should step up. Actual and personal experience is best.

 

[Hugnot]

Bullets having longer bearing surfaces would have higher sectional densities than other bullets of same caliber & length.

A longer bearing surface surrounding lead core would shorten the separation of center of mass & center of pressure and result in adequate stability with slower twist & increased bullet weight, provided bullet length is unchanged.

G7 Form Factor = SD/BC

Like a lower value is best with values shown with green, yellow, red backgrounds in Berger display.
My display has Hornady bullets shown in red.

I made this spread sheet to show this:



Some 6mm bullet G7 Form Factors from Berger:



Longer bullets may weigh more but this does not mean a corresponding reduction or improvement in the form factor (drag reduction) as FF = SD/BC. The SD (sectional density) would increase with weight and without a corresponding increase in BC the FF (drag) value would be higher.

The new Hornady ELDVT bullets have good FF values:



The 62 Grain .224 ELDVT bullet has the lowest FF (drag) of all .224 bullets using Hornady's G7 BC number, .199.



Using a 7.7 twist .22-.250 with 34.0 grains of VN 540 I get just under 3,675 fps. Max velocities with the 88 grain .224 having a G7 BC of .274 would be just under 3,000 fps in my 7.7 twist .22-.250.

For the 62 .224 ELDVT the separation of center of mass & center of pressure are increased as there is a relatively large void between bullet core and plastic tip bottom. This results in a longer and lighter bullet. A longer bearing surface surrounding lead core would shorten the separation of center of mass & center of pressure - adequate stability with slower twist & increased bullet weight.

The Miller Sg calculations did not work as expected for the 62 .224 ELDVT. Hornady does not have a twist recommendation for this bullet.

.223 Rem, 62 ELDVT, 9 twist at 2950, Sg = 1.33, should be marginal stability with reasonable accuracy. No groups - no bullet holes at 100- many rounds fired.

.22-.250, 62 ELDVT, 7.7 twist at 3675, Sg = 1.94, "comfortable stability" Groups about 1/2 MOA at 100.




Actual shooting results & applicable number stuff.

Sg is- "A numerical measure of the bullet's stability, the stability factor Sg, is the ratio of the rigidity of the axis of rotation to the magnitude of the overturning aerodynamic torque."

The all knowing but stupid AI defined Sg as "specific gravity" - actual results but not correct - use AI with caution!

 

[Mark37082]

There are so many members on this forum that are willing to do the work and share their results and experiences. It is sometimes difficult to determine where opinions stop and actual results prevail, but I really appreciate the opportunity to learn from others doing the work.

 

[DocUSMCRetired]

Absolutely, and even more so when you get into super heavy for caliber subsonic. You can get 95% case capacity, push big boys, and stay subsonic.

 

[RockyMtnMT]

Weight makes bc. It is the single largest driver of a bullet bc. Increase weight and the bc will increase. You can gain bc from form but at a price of losing weight from a sleeker profile. You gain bc from better form but lose some bc because of lost weight. So, as the form factor gets better then the bullet gets lighter for it's length and then needed twist for stability must be increased. Lots of gives and takes come into play.

The heavier higher bc bullet started at lower vel will always at some point down range pass up the lighter lower bc bullet started at higher vel. The turtle always passes the rabbit somewhere down range. Sometimes the pass doesn't take place until well beyond the hunters long range limit. Sometimes it doesn't take place until beyond the bullets capability to perform terminally on game because the impact vel is too low.

Wind drift is a great subject. I find it absolutely fascinating. For years now we have been shooting long range and much of our long sessions have been for bullet testing. Often with very diff calibers and bullets at the same session. Inevitably I would find that I would almost always hold the same wind with all of the test subjects during the same session. I always chalked it up to "That weird" and let it go at that. Over the last couple of years of shooting and having conversations with people that I have a lot of respect for, I find myself in the camp that bc is not a very good predictor of wind drift. It is the only "formula" that we have to work with so we use it. The bc will give a pretty accurate prediction of how long a bullet will be in flight. The longer the bullet is in flight the more time the wind has to push it. The bc does not predict how much wind will impact from the side on a bullet profile and the geometry of the bullet. I think the the greater the surface area of the projectile profile the more the wind will effect it. I think the longer it is in flight the more the wind will effect it. I think the greater the mass of the projectile the less the wind will effect it. In other words it takes more force to move the heavier object.

One of the best comparisons that I've had was when we did our version of the milk jug challenge a couple of weeks ago. We had some great variations of bullets and cartridges there. The rifle that was least effected was the 7mm that Brian was shooting. He was running a 154gr Hammer HHT prototype at 3600 fps. This bullet is showing pretty high bc at .644 g1. This was by far the fastest rifle there with pretty high bc. Brian did not have to make any wind correction until we got out past 500y on a milk jug. The greatest comparison was me running an 89g .257 cal prototype with a bc that is running pretty close to .400 g1 at a vel of 3450 fps. I was shooting next to @bigngreen running his 30 Sherman with a 245gr Berger at about 2800 fps. (I don't remember for sure his vel) He and I were holding the same wind out to a bit past 800y. My 7-08 running the 145gr Hammer HHT at 2700 fps was the most effected of all the rifles we used. It was the slowest and lowest bc bullet being launched. It had them most time of flight. This I expected. Even at that we are talking only a small difference. Maybe a couple of inches. I really wanted to see if I could be proficient with it out to 400y or so which is what I built the short light rifle for.

That's my .02.

 

[IridiumRed]

The above post (not quoting it due to length, just making thread scroll faster), is very good food for thought. The core take-aways, for me, being

1. How little variance there is in actual wind drift between many of these competing options at medium ranges (500 yards), going long heavy and sleek or really fast and

2. The idea that bc isnt directly a good predictor of wind drift... and that time of flight is more important.. but there are other variables going on there. Shape of the bullet, surface area from the side vs its weight...(getting into its density from the side) i feel like there needs to be a "side profile ballistic coefficient". Has anyone gotten seriously into going down that rabbit hole, of trying to look at what -really- drives wind drift, from a technical viewpoint? Im kind of quietly chuckling to myself thinking "what i should ask is what does Brian Litz call this, and what book has he published his thouggts / research in?"

As far as #2 goes, im -guessing- that in real life that many of these various factors cancel out, at least maybe until long range (maybe seeing little appreciable difference at 500 yards, noticeable difference at 1000). The short fast bullets with poor(er) bc having smaller side profiles and shorter TOF, and the long sleek heavies with great bc are slower with longer TOF but have more side area, but also more weight (which may or may not be enough to offset that extra area, probably driven by density from a side view?)

Anyways, this made me think of a few things that i hadnt really thought of before, and sure dont have good ideas on.. again... good food for thought

 

[Phil Rizzo]

Good stuff guys, keep it coming

 

[MagnumManiac]

Magnum mania, Please explain why, in your opinion, heavy for caliber bullets must have a muzzle velocity of at least 2800fps.

My reason is quite simple, it holds velocity at extreme range better.
My 375's running 400+g bullets at 2950fps hold onto velocity like a politician holds onto a bribe. If the velocity starts at say 2700fps, have a look at the extra drop and wind drift…
I developed my own cartridges to shoot to 2k comfortably, even 1 mile, the drop/wind is definitely a factor.

Cheers.

 

[MagnumManiac]

What a lot of people forget is that BC is not a constant. If you shoot that bullet faster than the velocity it was tested at, the BC will be higher and all other factors like drop and wind drift will be less.
There is real reason to try and get as much velocity as you can, but there is always a point of diminishing returns with larger case capacities…

Cheers.

 

[RockyMtnMT]

@MagnumManiac is right on. Big guns running big, heavy bullets won't get beat by smaller guns running smaller lighter bullets at similar velocity. Smaller stuff can close the gap with higher velocity and often win to ranges far beyond hunting capability. Eventually the rabbit gets passed, just depends on how much head start he gets.

My point is drop is very predictable given current technology. Wind is not. I encourage guys to shoot different stuff on the same range session and see what happens.

 

[MOA or bust]

Magnum maniac,
When you state that a heavy for caliber bullet MUST have a MV of 2800 or greater, I guess you are only sharing your personal requirements, right?

I am working with a new 7 PRC (Defiant Classic/Proof 22' CFB/XLR chassis) that is slower than expected after 60 rounds. I can only get 2850 fps with Barnes 168 LRX (G7 2.57) and 2730 fps with Berger 180 VLD-H (G7 3.45).

If I want to have minimum impact velocity of 2000fps and 1500 ft/lbs for elk, the ballistic tables suggest the slower/heavier Berger would give me 100-150y more range.

The above rifle will be a backup for my 28NOS (170HHT@3150s) for upcoming elk rifle tag.

 

[Phil Rizzo]

I think he means the faster it starts out the longer the effective range will be, in general.