Long range shooting formula, ballisitc coeficient etc

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Sentryau2

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Ok so before I start I just want to say that I have poor math skills and I am NOT and do not plan to be a real long range shooter. I just would really like to be able to do the calculation and formulas that I would need if I did want to be a long range shooter. I am toying with the formulas to calculate sectional density so I can calculate the ballistic coeficient.

The round I am searching this for is the 9x39mm russian (simply because I like the aspects of this caliber and info on it is hard to find.)
weight=17.3grams velocity=310m/s

So far I've got the bullet diameter .354 weight 267 grain velocity 960ftps
I was trying to calculate the ballistic coeficient and I ended up with .76 (can someone check this please?) I would also be greatfull if someone could give me an accurate formula that would work to calculate the BC of any bullet with limited knowledge.


Here is what I got with the formula SD over I = M over drag coefficient squared.

So for SD weight in lbs .03814 divided by the diameter squared (.354) so .125316 which comes out to .30403 which you divide by the drag coeficient
.30403/.04 so the BC is .76 or am I totally off track here :confused:

Is there any better/easier formula? Could someone give me some tips on long range shooting. I know the best way to get good at it is to do it, but thats not really an option right now and I still want to know how to do the formula by hand. What else do I need to know if I wanted to be a long range shooter or "sniper" if you will. Is spin drift really a problem? The earths rotation?
 
BC is not somthing you need to calculate, nor is that the right formula. BC only pertains to the bullet itself. I'm not sure the BC of the round you are talking about but I can almost assure you it's not .75. Most ballistic calculator have the tested BC of given bullets and you input zero range and velocity. With known dope at diffent DA's all that is left is making a correct wind all and squeezing a good shot.
 
If I had to guess I would say the BC of hat bullet is close .1-.2 range. Not ideal at all for long range
 
I meant the BC of the bullet. How would I calculate such? Yes but in a situation where you could NOT rely on technology (which is not at all uncommon) how would I calculate it? I already know how to do range estimation with mildots.
 
The closest thing I can find is a 286 gr 9.3mm bullet. It has a BC of .400.

http://www.hornady.com/store/9.3-Cal-.366-286-gr-SP-RP/

A 267 gr 9mm bullet would be fairly close. But bullet shape can make a significant difference. For example a 180 gr RN .308 bullet has a BC of .241, a 180 gr Nosler Ballistic tip is .507.

Just look up the BC of the bullet you want from a manufacturers specs. You are making this a lot harder than necessary.
 
yeah, the calculations will get you in the ballpark, but actual measurements (see Litz' doppler radar) are useful. granted, you stated you were not interested in using it, so i can't help you with the calcs. as kernel said, you can shoot the thing at long range and measure the drop and velocity with a good chrono and then back into the BC until you find a number that matches the drop and velocity
 
I will use it just not to actually take a shot. The max range I have is 100-200 yards and thats IF I feel like walking through the woods. (my yard is a literal forest) How do snipers calculate the info they need?
 
Exterior ballistics calculations involve differential calculus and I was never really good with that, barely passed it. :rolleyes: However, back in the early 80s I had this Timex Sinclair 16K computer and wanted to see if I could develop an exterior ballistics program, but didn't know the math. I'd ask engineers and work and they'd go into their engineer routine, which if you don't know engineers, is to baffle you with BS if they can't dazzle you with brilliance. Makes 'em sound smart. :rolleyes: So, I called Sierra because, at the time, they were running magazine adds saying "ask the bulletsmiths" and gave an 800 number. The guy says he has this article he'd send me that will give me the derived calculations. It was an article in Rifle magazine from a PhD mathematician from New Mexico State University. He had derived the math to simple algebra. Well, the calculations were algebra, but a bit long winded. All I had to do was put them into a BASIC program and format the output, but that took probably a month to write and debug. :rolleyes: I had Fortran and COBOL programming in high school and a Fortran 77 class in college, but I'm no professional programmer. My wife has a PhD in computer science and gets over my head all the time in conversation. LOL Anyway, it worked, but if I had to do it all long hand, it'd take all day for one trajectory chart. :rolleyes:

I really liked my program, still have it, but chunked the last computer I had that had a BASIC compiler in it. I set up the thing to do all the statistical analysis, too. But, probably less than 5 years after doing all that, there were exterior ballistics programs offered for the newly invented PCs. :rolleyes: They did all what my program did AND stuff like wind drift which I was too lazy to write, recoil calculations, such as that. I have a freebee I downloaded off the net in this computer, does trajectories, velocities, energies, etc, but doesn't do statistical stuff like standard deviation which is important in load development. Works, though.

Now, I always just used the BCs given by the manufacturer of the bullet, but you've already been given how you would calculate the BC. The expensive Ohler chronos have a sound detector in a triangle that one puts up down range around the target and of course the sky screens. The sound detector detects the bullet as it passes, helps if it's supersonic I'd think, and gives time to distance and calculates your BC for you. It also has a video that shows you where the bullet hit (triangulates the sound with the three detectors) and will show you the group and groups size! MAN that's fancy!

Me, though, I don't really need anything that fancy and expensive. I'm going to get a new chrono to replace my 30 year old Shooting Chrony. I'm looking at a Pact Professional. It prints a trajectory table and has a data base of bullet BCs in it, you select from the data base. It's a bit over 200 bucks. I now have my range in the back yard, live out in the sticks now, and I can load rounds in my shop, wheel around and shoot them over the screens (no range trips) and get instant data. My shooting bench is at a window in the shop. :D This has kinda been a dream of mine over the years. Also have a deer stand/feeder and a hog trap back in the woods, but that's another story. :D
 
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I would just measure drop at certain distances, get a chrony reading at the muzzle, and play with the BC setting on a ballistics calculator to match your drops. It was mentioned above, and the easiest way. A match bullet in 30 cal, will get upwards of .5+ in its BC, your bullet will not be close to that I guarantee;)
 
Or, why bother with calculating BC or drop tables if you're going to shoot at different ranges and measure drop? I mean, this is the old fashioned way, try it and see, then practice. :D Worked for the buffalo hunters. They didn't have ballistics calculators and a .50-110 drops like a rock. Where this stuff comes in handy is if you don't have a 600 yard range. Now, realize, too, that BC specified by the bullet companies is an AVERAGE calculated at sea level at 72 degrees F or some such. It varies with air density. If you're up at 10K feet shootin' at a mountain goat 600 yards off, your drop tables shot down on the coast in 100 degree heat are worthless, even if if you calculated your BC there. I guess you could test air density and adjust your table accordingly. I used to do that when jetting my racing two strokes at different tracks, but I don't have the time when an animal needs to be shot.

Nothing beats practice and experience when ranges stretch out. I keep mine under 400 yards even with flat shooting calibers, just too many variables beyond that. I think for the OP's questions, though, just mimic the buffalo hunters and shoot at different ranges and burn a lot of powder....experience with the rifle. :D I guess if you're not trying to kill an animal, it ain't so critical, though.
 
BC has nothing to do with drop. All bullets drop at the same rate. Every 9mm bullet drops at the same rate as every .30 cal. bullet. Which is exactly the same rate as every bowling ball and every ham sandwich. Newton figured it all out long time ago.

BC is about V E L O C I T Y. Speed. How fast it’s going. If you know velocities, and a starting vector (the degree the barrel is pointed up, down, or level) then Newton’s equations will show where the bullet is on an X-Y axis for any given moment in time. Add the Z axis and you got wind drift.

Forget this physics stuff. The OP just wanted a drop table for his semi-mythical flavor-of-the-moment subsonic 9x39. Here’s what I got, based on your BC of 0.76 (might not be to far off for a subsonic super heavy semi-mythical 9mm), a MV of 960 fps, and a bullet weight of 267 gr. Plus (more than) a few other assumptions I won’t bother you with and…. presto:

232323232%7Ffp54392%3Enu%3D3645%3E%3A57%3E257%3EWSNRCG%3D366899%3A2%3A5348nu0mrj.jpg

The Mantunas Optimum Game Weight Formula predicts a load that would be highly effective on game animals up to 90 pounds.

Zero at 100 yds and it's 4 inches high at 50 and 38 inches low at 200.
 
what exactly do you mean semi-mythical ? Its a real world caliber loved by the russians. Ive fairly well got things figured out for what I needed. Just took a few hours of searching and research. For the kind of shooting I eventually want to do there is a program I downloaded on my phone that gives me the info I would need to take a shot, and ive also learned how to calculate it on paper. I am familiar with shooting at semi long range, I just wanted to learn about bc and the things I would need to calculate if I wanted to take a shot at say 1200yards. I have that now (most of it) but I'm still working on spin drift. Is that a real problem with long range shooting? I mean I know wind drift is. I get to go to a relatives house in about 6 months and they have mile long dirt road (that goes no where) that they use as a range so I will be getting to do some long range shooting, the only bad thing is I dont have a decent scope or gun for long range so I will be borrowing one of theirs just to see what its like. I will post my experience.
 
BC is really about drag, slipperiness, which determins how fast the thing will slow down. So velocity, drop, is surly part of figuring it out. Mythbusters had a great demo on bullet drop, and gravity does pull everything the same. Wind resistance however, does play a big part....
 
Out to 200 yards I suspect you're guilty of over thinking the whole thing.

To get a feel for the parameters involved in calculating a shot go find the "external ballistics calculator" found on the Hornady web site. One of the boxes at the top of the page is "basic" or "advanced". Click on the "advanced" and take note of all the factors that come into play.

Input numbers that are realistic over a range of options suitable for your situation and then calculate the table of results for each. It'll soon give you an appreciation for what is important and which factors have minimal effects. And best of all it avoids having to do all the math! :D

The long distance snipers take into account all the environmental issues noted on the advanced settings page both in terms of weather and rise or fall to the target. For them all this stuff makes a big difference. But out to 200 yards? Not so much unless you're shooting in Class F or something equally demanding. The one factor that does make a big difference being shooting up or downhill.

And the BC of a bullet is more than only about the cross section area and weight. Shape also comes into play and is quite significant. In the end the only truly accurate way to measure BC is to put two chronos out at different distances as suggested and get readings.
 
How do snipers calculate the info they need?
Click to expand...

They are given the BC of the bullets that they are using and then input it into digital tools.... If they don't have that available to them then they already have a range card and a full data book of previous shots that tell them the information that they need. The only "calculations" that they may have to perform without technological help is windage effects (and that is usually done by an educated guess from an experienced shooter) and a calculation using the reticle when a rangefinder is not available.
 
Kernel,

On the Optimum Game Weight Formula, they list BTR-60 (right after rhino / elephant). Isn't that a russian APC??? :D
 
You really can't calculate a Ballistic Coefficient based on diameter, weight, and length alone. Bullet shape has much to do with it. One can calculate Sectional Density but this isn't as critical when shooting long range as BC is. For someone with "poor math skills" you undertaking a huge task!
 
I did a bit of studying and I've got it figured out for the 5.56 I think. I was able to find a few guides at useing mils to calculate bullet drop. I was able to find the formula for wind and for moving targets. I will never really shoot past 600 yards so do I pretty much have everything figured out that I need? Other then lots and lots of practice.
 
Sentryau, spend more time shooting and less time posting. Long range shooters start with the basics, calculated BC, velocity, wind drift, drop, altitude density, range. Those using ballistic computers will enter the info and get their basic dope. They'll take their shot and enter corrections according to the results to fine tune their data. The more shots they take, the more data they enter, the more accurate the results.

They also learn through experience. Carlos Hathcock, one of the most successful snipers was asked how he figured his dope for a very difficult shot he'd made. Carlos answered that he studied the terrain, watched how the wind shifted by studying the heat roil and used a lot of SWAG. Puzzled, the interviewer asked what SWAG was. Carlos smiled and answered "Scientific Wild Assed Guess!"

Carlos Hathcock had done so much long range shooting, his experience let him figure shots that should have been impossible. You can ask all these questions until the cows come home, but you won't understand the answers until you go shoot.

It will help you tremendously if you go study books on ballistics. There are a few good sources on the internet, but none have been as good as the books I've read. On real good source is an old Sierra Reloading Manual. Recent Sierra manuals lack the ballistics tables found in the old manuals. Sierra now makes the tables available as a program. I learned much studying those tables
 
what exactly do you mean semi-mythical ?
Click to expand...

Well, for starters…….

No known commercial rifles or pistols chambered for it: check. No factory loaded ammunition. No standard reloading dies. No suitable bullets from the major domestic manufactures. Check, check, and check. No reloading data published in the primary hard copy books or on the major manufactures web sites. Check.

No SAAMI pressure specs or chamber dimensions. Check. Blogged about by 14-year-olds on Call of Duty fan sites. Check. Preferred suppressed bullet-hose round of the Russian Federation’s super secret Spetsnaz, KGB (pre 1991), and Internal Affairs Ministry. Check, check, and check. Legal for unicorn hunting in all 57 States. Check.

If that’s not a semi-mythical flavor-of-the-moment cartridge, I don’t know what is. Not that that’s a bad thing. Every gun owner and handloader should have at least one unconventional round. I’ve had a half dozen, though none as ambitious as yours. So, I say, “Go for it.“ Follow your internal muse. Somebody’s got to hunt those unicorns!
 
By the way, getting back to the BC of your bullet based on the info in the first post I'd say that you're wildly off at .76 for the calculated BC. Just compare around to similar bullets from various makers to get a ball park estimate.


For example here's a link to a Hornady .358 250gn bullet which has a BC of .375.

http://www.hornady.com/store/35-Cal-.358-250-gr-SP-RP/

That's a HUGE way from your .76 calculation. So either you messed up the number crunching or the equations you found do not fully describe the process.

For giggles I plugged this BC and your sub sonic velocity numbers into the Hornady external ballistics calculator. Now you first of all have to stop and realize that a sub sonic round is not going to work at all well out past about 200 yards. The velocity and hitting power will have dropped off dramatically. And even at 200 because it's starting subsonic to begin with the trajectory is going to resemble a rainbow even at 200.

For example with a 100 yard zero at 50 yards it's going to be 4.2 inches high. At 200 yards it'll drop by 40 inches. This being based on your bullet weight and speed from the first post and the Hornady BC of about .38. And in fact if you look around at the various bullets in different sizes you'll quickly find that only the longest heaviest and most slippery of them are up around .6.
 
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