Ballistic charts never seem to work...WHY?

C

cj Lamb

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I Shoot a 338 LM 250gr MK and use a 12X42X56 NightForce Benchrest scope. When ever I try and use a ballistic chart or calculator it is never on. I have even tried to use what my actual bullet drop and or clicks on scope are to adjust the velocity on the chart to maybe match but that never works either...any ideas?
 
cj somehow you've got an input problem. The various ballistics calculaters are wicked accurate. One of the big items which often gets forgotten is that it's important to plug in the distance from boreline to center of scope. Default is often 1.5" which is probably a half inch off in your case. Some simple issues I've seen which screw with actually hitting stuff are canted scopes, scope not over the bore and the real biggy is shooting without a level.

I use published BC's even though I have three chrony's and access to a 43 setup.

I use the Shooters Chrony's with excellent success. You wanna' REALLY make 'em bulletproof go buy some lights to hang over the skyscreens. costs about 20 bucks from Lowes for the parts.

anyway, it's an input problem somewhere.....

al
 
My range has buried RG6 and CAT5 for the Oehler 43 setup. And power down to 100-200yds...... My buddy moved away with his Oehler 43 so the closest one to me is 6 miles away on another range but I've never felt hampered not the need to drive the 6 miles.

That said I recently stacked 3 Chrony's back to back and shot over them. You get the light right and they're fine.

I too have shot them with an Oehler 43 to 'proof' but in the end all I care about is relative velocities anyway. A 15fps absolute difference won't even show up in any real-world shooting situation. Head/tailwinds vary more than that (and no one plugs them in) and in any event only one shooter out of 100,000 will ever see an ES of less than 45fps absolute.....

YES a good Oehler setup could bring my absoluter resolution down by a factor of 10, from 15fps to 3fps but I just don't need it! My relative resolution is down in the dirt. I "proved" this by shooting many rounds over the three backed up chrony's.

al
 
goodgrouper said:
The problem with the three backed up Chrony's is that although they may all agree with each other, they may all be fast or they all may be slow. I can buy three Swatches (remember when those were cool?) that all say it's noon straight up but if the real time is 12:01, then I'm going to be late three times!
Click to expand...

Three different models, all different yrs mfgr, all in agreement within 6-8fps, all showing velocity decline........ it's a perty good barnyard test.

as I said, if they're all 15fps "slow" or "fast" I don't care.

if they DIDN'T agree we'd have a problem!

The problem with the Oehler 43 setup is time of setup.... I'm waiting until I can build a permanent home on the 100yd butt for the acoustic target before going to the trouble.

A fellow named Henry Childs used to post in detail about how to set up and calibrate the Oehler setups. I've got pages of his posts and pictures as well as email correspondance so when I AM ready for a permanent installation I'm all set but for now the lighted Chrony's do what I need.

Again, I DO shoot out to longer ranges. I can shoot 600, 1000 and 1400 on my own property. I've never had any trouble getting on paper. ON and within 6-8 inches vertical. And this is shooting down a mountainside where I have to guesstimate elevations. All's I'm saying is, the programs are spot on. Give any decent program good info and it'll get you within an inch at 600yds....... IF you and your rifle system are capable. I'm capable, with my equipment, of 1/4moa with chamberings from .22BR to 338 Lapua Improved and with my vel nailed down to within even 50fps ( +- 25 absolute, ES in single digits) it's just not a problem getting on, except that I'm 'xceedingly math challenged so I often screw up my crankage!!

BTW I was playing with a 338 hotrod today (between posting here) trying to get the new 300gr hybrids up to 3000fps (Over My Miserable Chrony ;) ) and I blew my home-ade muzzle brake clear into the swamp. Pieces of brake everywhere, just the ring left on the barrel......... So I fired the next 6 rds without the brake.

HOley kuhhRAPPPP!!!

As I'm typing now I've got this awful knot twitching sporadically behind my sta'board collarbone. My neck feels like I've been in a car wreck.

Manalive I detest recoil.

al
 
Ballistics is (are?) nothing more than physics. Garbage in, garbage out. Your problem is most likely your input but, what difference does it make anyway? The output should only be used as a guide, not gospel. Believe the holes in the paper, not what the chart says they should be.

A $500 chronograph can be just as inaccurate as a $100 one. And vice-versa. This is 2011. The cheap chronos are not what they were 25 or 30 years ago. Anyone who thinks that the output from an expensive one is any better than from a Chrony or a PACT is only fooling themselves. (See above "Garbage in, garbage out".) And that's the truth.

Some guys like to play with chronos and even get to the point of playing with them more than they shoot. Not that there's anything wrong with that. But they are only one tool. I'd rather spend $100 on a chrono and $400 on components than the other way around. But that's me.

Just my farm boy opinion from 50 years of chrono experience. Yes, I'm that old!

Ray
 
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I hate to admit it but I think Al is spot on in his first post.
I'll add that I think you will get better results with the low drag bullets if you use the G7 BC with a Balistic Calculator that supports G7 BCs or alternatively use mulitple G1 BCs like Sierra reports.

James
 
Chisolm said:
.................... or alternatively use mulitple G1 BCs like Sierra reports.

James
Click to expand...

James brings up a point, at ranges beyond 500yds actual "flight characteristics" may have an effect.

"BC" is exactly as it's described, a coefficient, it's NOT a measurement. It's a comparison. So.... using G1 VS G7 isn't really as big a deal as it's cracked up to be EXCEPT that beyond a certain point the flight characteristics of dissimilar bullets will diverge more and more...

For example let's say you wanted to check the "Acceleration Coefficient" of yer Ferd pickemup truck against a standard.. (this is how coefficients are established. The standard for G1 is a 50cal projectile that's just been assigned a value of 1)



For the "G1" comparison you'd compare yer Ferd with a rig that the tester is very familiar with, and a rig that's reliable and repeatable. A baseline. Could be another truck, could be something else entirely, maybe a Porsche 911 that runs like a clock...

Whereas for the "G7" comparison you would compare against another standard, maybe "the 2011 Truck Of The Year" that the pertickler magazine picked. So it could be said that the G7 comparison is more similar, and under some sets of conditions this will be true.

My point is, the "coefficient" part is key. A .521BC bullet (G1) simply flies "52.1%," or just over half as well as the standard 50cal used for comparison. The same bullet may well map as .255BC using the G7 standard.

I still think the problem is GIGO

al
 
goodgrouper said:
Sorry Ray but that just ain't true! If you dealt with chronos in the way that I have you would have seen vast differences in them. For one, they all absolutely DO NOT use the same photo cells. The cheaper units use cells that are of much less quality (which is why they have more problems on bright days and sun angles and need the help of lights over the diffusers). Also, the circuitry is not the same in every unit. When you buy an Oehler, you are essentially getting two chronos in one. There is a proof circuit that compares readings between the two sets of screens. Your Anyotherbrand does not have this. Then the Oehler also gives the user the ability to put the screens farther apart on a custom rod which further increases the accuracy of the unit. The cheaper units are stuck with one foot or two foot distances and that just simply isn't as accurate.
Click to expand...

OK, let me try this ;)

NO, THE CHEAPER UNITS AREN'T AS ACCURATE!!!! But here's the deal......

Let's say we're measuring a distance of 1 yard.

We can use a yardstick

We can use a tape measure

We can use a little laser unit

We can set up a sheet of flatstock, get out the Dykem and the scribe and measure with a machinists rule

WTH, once we've got the flatstock out we can use calipers. We can check with a micrometer.

But to get REALLY accurate we'd have to gage it and in any case the "accuracy" is relative to what we need. With even the first method we're within a fraction of 1% which means that if we're making something that has some tolerance we're in the clear.

IF my chrony is off by 30fps on a 3000fps load than my absolute accuracy is within 1% which is more than good enough to get me on paper. Try it, plug in a 30fps difference and see how far out you have to be for it to show up. IME you'll see about 6" at 1000yds which coupled with the BC standard variations could well be a total of 1ft "off" of the chart. Still a GIGO problem but not a very big one!

Dude could spend a grand on a chronograph and be shooting a 1moa rifle....... where's the gain?

al
 
Goodgrouper

What Al said.

And, as I said in my first post, what difference does it make. In the end, everything is accepted, or rejected, based on actual firing at real targets. A few fps either way isn't going to make much difference. And that's assuming that all of your other input is accurate. And that's a big assumption.

And how can you say positively that one chrono is more accurate than another? If my PACT reads 3150 and your Oehler reads 3160, which one is correct and how do you determine that? Surely not by how much the chrono costs. My $100 PACT does things that I never would have imagined were possible in 1960 when I had a $500 ITT counter chronograph. Both probably had more built-in accuracy than I could get out of them with my set-ups and shooting techniques. GIGO still rules.

I have nothing against guys who like chronographs and enjoy playing with them. Every sport can be compared with NASCAR. Some like to design cars, some like to build them, some like to work on them, some like to drive, and most just like to watch.

And then, there's that little puff of wind downrange, that you didn't see coming. :rolleyes::cool::(

Ray
 
I have been reading along, now you guys have my attention, What is the story on the hybrids ? As soon as they came out I grabbed some, before I got to try them , got the news of 2900fps and under. I gave them to a buddy who has a 338Lapua in ar30 perfect. Now you say they blew the MB off ? I think I will wait for more testing
 
Bob Smeltzer said:
I have been reading along, now you guys have my attention, What is the story on the hybrids ? As soon as they came out I grabbed some, before I got to try them , got the news of 2900fps and under. I gave them to a buddy who has a 338Lapua in ar30 perfect. Now you say they blew the MB off ? I think I will wait for more testing
Click to expand...

LOL!!!

I BLEW THE HOME MADE MUZZLE BRAKE APART because I built it too light for this beast. I'm trying to design a quieter and lighter and tunable brake that actually works to reduce recoil (unlike the BOSS)

This rifle system KICKS!

My design is fine, the bullets are fine up to 2900fps so far....and I'm still shooting free recoil in a 20lb gun.

!!!

Blown up brake has absolutely nothing to do with the bullet.

al
 
I don't want to rain on anyones parade, but all things being equal (210 vld 3000fps, 1200 ft ele, std baro, 300 yard zero, ect...ect....) and change only the sight height by 1/2 inch....from 1.5 to 2 inches (33.3% differance) the impact diff is only 1.17 inches...from 221.02 to 219.85 at 1000 yards according to the Infinity 6 program. I would not sweat this part of the "garbage in/out" theory. You have other problems.

Tod
 
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Cheechako
Ray I am with you on this one 100%.
i shoot at targets that run away but have figured out a way to prevent that for the most part.Once I start reading about the first shot cold barrel I only shoot them in the neck or head stories my eyes start to glaze over.
Lynn
 
Tod Soeby said:
I don't want to rain on anyones parade, but all things being equal (210 vld 3000fps, 1200 ft ele, std baro, 300 yard zero, ect...ect....) and change only the sight height by 1/2 inch....from 1.5 to 2 inches (33.3% differance) the impact diff is only 1.17 inches...from 221.02 to 219.85 at 1000 yards according to the Infinity 6 program. I would not sweat this part of the "garbage in/out" theory. You have other problems.

Tod
Click to expand...

Tod, this depends on your zero..... picture it in your head. If you do your work at 100yds like most people the difference is larger.

I call this the "crossover point," the place where the two rising trajectories coincide.

In other words, with a 900yd zero the difference would be tenths of an inch at best but with 100yd zero (or say you input 3" high at 100yds as your reference) your crossover point is closer so your divergence will be greater.

I first ran into this when some quasi-military guys were complaining that the PBR on the new flattop AR receivers was 'way shorter than what they were used to when they mounted their scopes on top of the handle......

Draw the two trajectories on paper, just two similar arcs passing thru the LOS at 100yds with one starting below the other to see the difference. Draw the same two arcs but with the crossover further out to see the effect diminish with increased distance to "zero." (crossover point)

al
 
Tod
Al is right if your zero is at 100 yards it will be off by 4-5 inches at 1,000 yards.So if your only error is the scopes height the difference between the two bullet paths will look like one path above the other both touching at 100 yards and 4-5 inches apart at 1000 yards with no crossover points along the way as the faster bullet will always be on the top.
Lynn
 
3.87 in dif with a 100 yd zero. With a lr rig, why on earth would you have a 100 yard zero. In some cases I CAN'T have a 100 yard zero? Even if I do my load work at 100 I use my 300 yard zero....I don't want the bullets hitting where I aim....it destroys my aim point.

Also, I fully understood the crossover thing...and with a 300 yard zero, and the distamces to which I shoot now days (under a mile) it is a moot point (for me). Also, I Measure all of my sight heights when I assemble each rifle, so again...moot point for me. Also 4" miss at 1000 yards...still a kill, so again, moot point. And if you are in a match...you got 6 min and unlimited sighters to adjust for your 4 "...but of course, the light changes and wind changes won't affect your impact point ....oh ....wait ..um...they do affect your vertical impact points...a bunch, so....moot point...again. A 20 fps diff in velocity will change me 3.98....so moot point....

My point ( which may be, by now, moot to you guys ;) ) is that, although I measure sight height to within .001, I don't really NEED to.....I am just trying to eliminate as many problems as i can to assure my first shots are "kill shots". And as you guys know there are a brazillian different things that can go wrong that creat more than 4" @1000 problems. Also, I am as anal as they come,,,:eek:

Just sayin.

1/2 action diameter + ring/base height from action to botom of scope + 1/2 diameter of scope = scope height. Should be to within .001" .
 
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Different worlds Tod :)

First of all I never "zero," anything..... at best it's a floating zero, a reference for the next day, to get on paper. On a given day if my rifle's within a foot side to side I figger I guessed the conditions perty good! Now once I find the paper and where I want to hit I expect my equipment to be able to deliver 1/4moa or less. This is "pretty accurate" by most standards! ;)

The reason most people do their work at 100yds is two-fold;

#1- many folks only have access to 100yds on a regular basis and
#2- many people speak in the language of "come ups" and these are generally expressed at 100yds.

For myself I do most of my development work at 100yds even though I can shoot out to 450 off the same bench in my yard. Because I can actually see what's going on at 100yds..... anything beyond that is a waste of time except for verification of level and tune. (for ME) And shooting at 450+ yds is done in bursts, trying to outwit the wily pool.......YES, I just stated that shooting at long range for load development is a waste of time......

IMO

No I don't "zero" anything at 100yds either, in fact I walk groups all over 2'X4' sheets of blueprint paper...... but I fully expect to be able to shoot a fly if it lands. And often do.
I'm not big on "zero's" and PBR's and such

As I said, different worlds

al
 
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