Custom BC's?

[stagpanther]

I just received an e-mail from Applied Ballistics discussing their new approach to calculating BC/SD--basically "abandoning" the notion of using the G1 or G7 "canned" profile for calculating trajectories. As far as I can tell (I'm not the sharpest pencil in the box)--they're using data from from their Doppler hardware and software plot calculators to get massive quantity of data points to "fine tune" their calculations. I'm at a bit of a loss understanding how the custom BC calculations can "discern" between physical properties of the bullet vs. environmental variations (not to mention the travel in the bore) to account for the custom/personal BC profiles variations from the traditional "canned" G1 or G7 profiles. Thoughts?

[hounddawg]

I might start worrying about that stuff if I ever strat shooting at ranges where the coriolis effect would need to be calculated but at the moment as long as I can get on paper with my android ap and G1's I am happy. Anyone shooting PRS on the other hand will eat this stuff up. The guys that try and hit a half MOA plate at 1000 yards on their first shot

[Marco Califo]

Hint: They want your money.
Another hint: You do not need what they are selling.
How much money did I just save you?

[stagpanther]

I'm interested in anything that makes long range shooting more predictable. I sort of figure that they are going to offer a personal BC for ammo submitted to them--and perhaps they are going to offer the custom BC's as an additional input, I would assume, in their ballistic calculating software.

My intuitive reaction is to what degree are the variances in BC attributable to conditions as opposed to variances in bullet's construction vs the "canned" G1 or G7 profile. Put another way, is the custom/personal BC going to be more accurate when used across a wide variety of environmental conditions than the simple G1/7 "templates?"

Here's a link to their article http://appliedballisticsllc.com/Arti...efficients.pdf

Kinda hoping Unclenick/Bart might shed some light...

[T. O'Heir]

Yet another hint: Listen to Marco. And e-mail 'em back and ask 'em what bullet, cartridge and rifle they used. Biggest risk doing that is they know you respond to their stupid marketing e-mails.
"...a half MOA plate at 1000 yards..." Done with a 105mm L7 gun on a Leopard tank. 1,000 yards is Point Blank Range for a tank gun. No walking the 1,000 yards to look either. snicker.

[HiBC]

I'm not bothering to keep up on the latest techs.
My younger brother shoots with folks who hang a two MOA triangle for a target in such a way that you don't see a dust puff to correct.You get two shots.
Brother uses his AR-10 T He shoots against "sky is the limit" folks.They use a 1000 yd range

One of his buddies has his own range and doppler setup.

The thing is the advertised BC on the bullet box is seldom exactly accurate. Advertised BC sells bullets.

Two reasonably identical rifles will show some variation in BC with the same bullet.

And of course,on any given day and location,temp,humidity,the barometer,ec will vary.

I've set my CED chrono with my target out to 500 yds and shot through it.at various lasered ranges to mome up with the most accurate data I could for that rifle/that load. I also recorded exactly how many clicks it took to get a zero for elevation out to a lasered 700 yds. I did not have doppler available.

When I had Kenton Knobs make me a custom knob,I had better data to give them than the sticker on the bullet box. With 20 minute bases and the 30 mm leupold tube,my knob was graduated to 1450 meters.

Yes,all the variables are still a factor. I did this in the late 1990's . We had less then. Springtime I was watching over calving,same ranch,same altitude.

Actually,if I could get a range,I could dial it with good results.

For any computer model,the more precise your inputs are,the better results you will get. To doppler the load/bullet you use out of your rifle is about as good as it gets.

When my brother put his 300 Rem Short mag top end on his rifle this year before elk season,he was able to develop a very accurate 180 gr (I think) LR Accubond load for it,then fire it (for free) through his friends doppler setup.

A very good picture of true velocities is recorded at several known ranges.

He is quite adept at working things out from there.

I'm curious if the strongly opinionated skeptics have actually used and tested these technologies,or are their opinions hot gas filtered through the foam in the couch cushion.

[hounddawg]

I think what you are missing here HiBC is that not everyone has the same goals. F class is shot at known ranges, it is pretty easy to develop a 300, 600, 800, and 1000 yard dope sheet for elevation. If I were a long range hunter or a PRS shooter trying to hit a clay pigeon laying on the berm at 1000 and my previous target had been at 425 yards a precise BC would be pretty important. Same for the ELR shooters, the guys who are reaching out 1500 - 2000 yards and beyond. I would say 90% shooters will never shoot at anything farther than 200 yards, so for them a $500 Kestrel would be about as useful as tits on a boar hog.

[HiBC]

houndawg: What I'm missing? I don't think I'm missing anything.

Same for the ELR shooters, the guys who are reaching out 1500 - 2000 yards and beyond. I would say 90% shooters will never shoot at anything farther than 200 yards, so for them a $500 Kestrel would be about as useful as tits on a boar hog.

I'm good with that. Different stroke,different folks. Actually,as I recall my Kestrel wind gauge was just over $100 a few years back.

I suppose now if you enter a few numbers they crunch everything.

We all have topics that don't interest or apply to us. My mousepad takes care of that for me.Just a couple of clicks . I don't mind if folks post something that's not my bowl of chili.

The OP has an interest and is trying to learn something.

I don't understand the rain on his parade.

Places like Colorado and Wyoming have some big stretches of private ranch and public land. For those who have access to it,its just another way to have fun. Its not just the 400 or600 or 900 yd known range points.

Once an accurate trajectory curve is created,enter 463 yds or 789 yds,etc and you get the data.

And,FWIW,....I personally don't consider hunting and shooting at longer ranges the same game.
I'll have fun shooting at a non-living target 4 times as far away as I would shoot at a game animal.At least!

A long time ago I loaded a floppy disc with the Sierra ballistic software into my 386 computer. There is a lot that can be learned.

Long ago,for Hot Rodders was a program called "Dyno on a Disc" It gave folks modifying an engine a tool to predict results.

You could build a virtual engine with specified heads,compression,manifold,carb,cam,etc and "run" it Then you could change the cam or alter cam timing or put on a different cam and "run" it again and compare results.

Its one way to find out the 1050 Holley double pumper and 292 cam might not be the best choice for a 63 Falcon with a 170 cu in six used to go to the grocery store.

Longer range shooters can study what a change in bullets and trade off of velocity will do.

But you are right. If there is no place to shoot over 200 yds,it might not be interesting

[hounddawg]

A Kestrel will only tell you what the conditions are where you are standing. I have seen 4 wind flags 200 yards apart with all 4 pointing in different directions. Fancy toys will never replace old school wind reading. A cheap meter might help you learn what a 5, 10, 15 mph wind feels and looks like and $20 bucks is a reasonable investment. Toss in a $150 dollar laser rangefinder and a Android ballistics ap that is about all anyone needs. AT a recent PRS match guys were hitting a clay pigeon on a berm at 1000 yards with no more than that. Quite a few nailed it first shot from what my buddy told me

I am not big on bling though. I still load on a Lee press and shoot guns I put together in my garage

[stagpanther]

Hmmm...maybe a bit of further explanation is needed here. Am I a competition shooter? No. Am I a long range target shooter? No. Am I a long distance hunter? No.

Then why the heck would I have any interest in all this high tech mumbo jumbo talk? 1) I might want to do those things one day if the opportunity presents itself; but most of all, since I reload everything, I'm intensely interested in anything that affects precision/accuracy of the cartridges I whip up.

Here's the other video https://www.youtube.com/watch?v=H9XjqEBoDk4 that was included in the e-mail in which Bryan Litz introduces his session with a background reference to the "100 yard essentials." Notice he frames the whole accuracy thing within the context of minute of angle--and how incredibly small that measurement actually is; which is saying as the range goes out your accuracy is measured by very small fractions of that initially small MOA.

That makes a heck of a lot of sense to me.

[Unclenick]

There are new sighting systems that use a laser to read the wind to the target and back, similar to what is done for adaptive optics telescopes to compensate for the mirage to get a sharp image. They combine that with range finding and atmospheric temperature and density measurements to show a dot in the display that predicts the round's POI wherever you direct it. They have inertial sensors that pick up the shooter's movement and add its effect into the POI calculation so that a shooter tracking a moving target has the lead automatically included in the POI prediction. The fact the Army hasn't deployed them everywhere tells me they cost a bundle or else aren't yet considered rugged or don't work reliably enough. But that's coming. Perfect ballistics are preferable for such a system, obviously.

The custom BC is not new thing. All the noise they are making over it as if it were brand new has surprised me. If you have QuickLOAD, you will have noticed the QuickTARGET Unlimited (QTU) 3 DOF exterior ballistics program that comes with it has a large number of drag functions for individual bullets. Most are Lapua bullets, for which Doppler data was gathered and published some years ago. There are also drag functions determined with other equipment by the U.S. Army Ballistics Research Laboratory starting all the way back in the 1940s. The late Robert L. McCoy eventually did them for all bullets used by the AMU and military snipers in the '60s and '70s, from 40-grain RNL .22 RF match ammo to .50 BMG. The Sierra 168-grain SMK then in M852, is included, as is the M1 Type match bullet used in the .30-06 M72 and 7.62 M118 (it is incorrectly labeled M188 in my copy of the QTU program).

The basic method of using ballistic coefficients in ballistic programs is based on math developed by Francesco Siacci and published in 1880 and applied to tables collected from numerous 19th century experimentors starting with Francis Bashforth whose work began in 1864, and including Mayevski, Krupp, and ultimately the Gavré Commission to present a standard projectile. Bullets and shells had less shape variety back then, so a single representative profile was easier to establish. The shape is dimensionless proportions that can be applied to any system of measuring units. In English units it is one inch in diameter and weighs one pound, so it has a sectional density of 1.00 and a declared ballistic coefficient of 1.00. A smaller projectile the same shape with half the sectional density has both less weight and less cross-sectional area to catch the wind. These differences cancel and it turns out to fly half as far when starting at the same velocity as the reference projectile or, in other words it slows down twice as fast. Thus, when the shapes are the same, the ballistic coefficient of a different size projectile is just equal to its sectional density. The same-shape bullet with half the sectional density has a BC of 0.50. A larger one with twice the sectional density of the reference projectile would have a BC of 2.00.

The trouble starts starts when the projectile you want a BC for isn't the same shape as the reference projectile. In that instance, drag effects don't change in the same proportion to Mach number as the reference projectile's do. This means, in addition to the sectional density of the projectile, you also need correction factors for any differences between the shape of the reference projectile and the actual projectile you are trying to compare it to, and that means different BC's for different velocity zones. These different velocity zones are exactly how Siacci and Mayevski accounted for changes in drag they did not then understand (crossing the sound barrier and above, which causes ballistic coefficients (drag correction multipliers for shape) to change.

Bryan Litz gets credit for being the first to publish widely about the fact modern spitzer nose bullets had much smaller BC deviations when they were scaled to the G7 reference projectile rather than the old G1 shape. The latter is a 19th century flat base, short ogive artillery shell shape. The G7 projectile has a long Spitzer nose shape and a boat tail. This meant just one G7 BC applied to all velocities would typically track well enough that you didn't need to break things out into velocity zones. It was the single most compact piece of ballistic information you could have.

Two things have changed. One is that computers have made shortcuts and substitutions and their associated approximations unnecessary. Today, even a smartphone has all the computing power it needs to compute trajectories from long, detailed drag function lists of Mach number vs. drag coefficient, and has the memory needed to to store a big pile of them. The second is that more bullet makers have access to Doppler radar with high enough power to follow a bullet hundreds of yards, so more drag functions are becoming available. This is a zero error trajectory prediction approach as they are no deviations from a standard shape when the bullet is its own standard shape. In that instance, a bullet has a BC of 1.000 compared to itself, so you use that number and don't worry about entering anything but your muzzle velocity, the range and wind and you've got it done. This is not a shortcut, like the BC is.

Then comes the final question, does it matter? That depends on what you are doing with the bullet. I took Mid Tompkins' Long Range Firing School class twice in the early 2000's and he mentioned that on a Palma rifle there was no point in having sight adjustments finer than 1/2 MOA because changes in wind happened so fast that by the time you made a correcting adjustment finer than that, the wind has already changed again. He just held off for wind changes smaller than 1/2 MOA. So then you have to ask yourself if knowing a trajectory for 1000 yards with higher accuracy than 1/4 MOA is really of any use. Art Pejsa's system, which requires a couple of measurements can get withing 1/2 inch at 1000 yards, but does that buy the shooter anything when the wind is moving?

This is going to be the big question about the fuss over actual drag numbers. They can give you more resolution than you can use and certainly more than you can rely on the box of ammo to be consistent about. Computers can easily be more accurate than the shooter or the gun, as long as the wind holds still or they have a way to read it instantly. How much of that the shooter can take advantage of remains to be seen.

[hounddawg]

How much of that the shooter can take advantage of remains to be seen

I know that my rifles out perform my technique ninety nine percent of the time. One hundred percent of the time when it comes to competitions, as soon as I hear the words "Targets Up !" my brain starts to short circuit and everything I have been practicing vanishes. The day a more accurate BC would be the biggest shooting problem I had it will be a good day for me. Right now I still working on turning the scope adjustments the correct direction

[stagpanther]

Thanks for that unclenick--I had actually forgotten about QL's custom bullet profile program.

[Bart B.]

Two things to remember when correcting for wind drift: wind speed ...

* only in the first third of target range causes over twice the bullet drift at the target as wind only in the last third.

* above the line of sight is faster than wind speed in the line of sight. Moreso in flat and smooth terrain.