Let's argue about BC's

[Buffalobob]

I will say a few things.

First and Foremost -- I give Paul respect for honesty and excellence in trying to turn out a really great bullet for long range hunting and hiring Brian to work on the BC issue. These are great bullets and work really well in the air and on the animals.

I have used shape factors and calculated BC and the shape factors work very well and are very close. If your BC is very far off the ones calculated from the shape factor go look in the mirror to find the source of the error.

The G1 BC of the Wildcat Bullet changes rapidly beyond 1000 yards and is basically meaningless at those ranges. All that matters is the G7. Under 1000 yards the 7 AM is so fast the BC can be any number your heart desires and you will make the hit. See all of my videos of me and my children making one shot kills with the combination of a Kirby Allen 7 AM and a 200 grain Wildcat bullet. YouTube - Canal de Microcystis. Once I began the quest to kill an animal at a mile I began to appreciate G7s. The sloppiness of range finders at those distance and the fact that I do not own nor use a chronograph nor weather station for measuring pressure complicate things but nonetheless each year as I acquire more data on bullet strikes at extended ranges it becomes apparent that the BC of the bullet is very good but is not miraculous.

Let us look at a few things. The shape of all the best VLDs is about the same and one can look at Brain Litz article on "Whats Wrong With the 30 Cal" on this forum. The best BC bullets have a major component of SD (sectional Density). So if the shape factor is similar then just look at the SD and see where it fits in the whole curve and that will tell you something about what to expect from a BC. In a 30" barrel 240 Wby I shoot Berger 115s at 3250 FPS, in a 28 " barrel 257 Wby I shoot Wildcat 130s at 3250 fps (G1 = 0.635) and in a 7 AM I shoot 200 Wildcats at 3350fps. All I have to do is to look at Brian's curve in that article add some SD here or there and instantly I have a good knowledge of what the BC is likely to be. The 130 gr 257 Wildcat bullets do not have a magically high BC but I use them for the simple fact that they are without a doubt the best BC 257 cal bullets ever made. They work great while traveling through the air and they work great on impact. Just really great bullets but no magic BC involved. I do not use a G7 with the 130 grain bullets because my Ruger #1 does not have the accuracy to shoot them effectively beyond 1000 yards.


As for LTLR and wind drift-- I sent Paul at Wildcat bullets a calculation on wind drift and if I can find it I will send it to you. Rule #1 is to calculate honestly. If you have to violate Newtons laws as did Light Varmint and the HAT bullets then I got no use for your calculations. None of this means that I or any other human are impervious to errors and I have made some expensive ones in my day. If you have to disavow the fact that Force equals Mass times Acceleration to get your wind drift then you might as well try to sell a porti potti as the Taj Mahal. Some people will buy it just as when Light Varmint said a bullet was like a drill bit. Stupidity is a prevalent commodity as WC Fields once commented-- a sucker is born every minute. So, fundamental Newtonian mecahanics have to have an application in this issue.

My only concern in life is whether at a range that is asymptotically approaching infinity, the bullet intersects the animal. Wildcat bullets are the best out there in many calibers but there is no magic.

 

[groper]

Using JBM's calculators, the velocity method is a lot more error tolerant - especially when dealing with the accuracy tolerances of chronographs. Plugging in the +/-.5% (accuracy tolerance of most chronographs) makes a significant change in the result using the time of flight vs velocity method. The distance measurement is also more crucial than with the velocity method. +/- 1 foot at 300 yards changes the result by 2% using the time method vs .1% (yep that's POINT one percent) using the velocity method.

The same guy also wrote this paper: http://arxiv.org/ftp/physics/papers/0601/0601102.pdf

Once I ran the numbers on the error tolerances… I switched to the velocity method.

I still buy you a beer if you ever come through Elko.

Paul,
You wont get any argument from me about shooting thru 2 chronies being a very accurate method of determining BC, but now im confused... If you were aware of accurate methods of determining BC, and practiced them, how did you not understand the reasons behind why Bryan revised your BC to .74 from 0.9?

I offered the acoustic method because its easy to setup... simply setup 1 Chrony at the muzzle and open up your laptop and start recording with its inbuilt mic for 1 string during your load development or whatever your shooting that day... When you get home, you can analyze the recording, do the math, and determine a real world G7 BC usually within 1% accuracy provided you payed careful attention to the details - namely wind vector, distances to the target are accurate enough with a decent laser rangefinder, measure the distance from your muzzle to the laptop within 1 ft, and air temperature.

But hey, if you dont mind the hassle to setup another chrony at the target, at long range and a shield for it, all the better... Both methods can give a VERY accurate BC result, PROVIDED you use a G7 BC calculation from the data.

However;
If you use the 2 chrony velocity method over short ranges, say 300yds for example (because we are lazy and cant be bothered setting up a shield in front of the chrony to do it at long range without risk of smashing our equipment) then go and use the velocity data in a G1 calculation - your only measuring the BC in the fastest part of its flight regime!- which will give you a higher G1 number than what is useful!!! The number you get, even tho its accurate, its only purpose will be to look good published on bullet boxs for marketing purposes...something us long range shooters grow tiresome of... If you must use G1 BC`s for your ballistics calculator, whether it doesnt have the G7 function inbuilt or the user is simply old fashioned, what we need is an AVERAGE G1 or multi velocity bracketed G1 number set, for it to be a real world and useful number that will give the user correct dope at extended ranges... which is the point, and is what meets the users needs - which is what Bryan gave us... Afterall, we barely even need to correct for elevation or wind at all inside 300yds of decent flat shooting caliber, so a G1 number for this part of the bullets flight regime is totally useless.

Be so much simpler if the entire industry would switch to quoting G7 numbers instead of the **** antiquated G1 crap...

Bryan Litz has done a great job in giving us the "real world" AVERAGE BC`s (over the entire 1000yd flight regime) that we actually NEED for so many bullets out there... any bullet maker who simply publishes the highest G1 BC at 3300fps - isnt doing any of us any favours, but it sure does keep Bryan busy sorting out the weed from the chaff...

 

[Michael Eichele]

Michael:
Once this is figured out, the rifle is taken to 750 yards. Just before it is fired at 750, a dead on 300 yard zero is verified. Then 750. In every case, when using this method bullets have fallen into the middle of the X ring at 750 yards.

JonA
Drop at 750 from a 300 yds zero is absolutely and completely meaningless as a method of verifying BC's.

Like hell it is meaningless. Use what ever method you like to determine a BC. The proof of accuracy is where the bullet hits the target.

Now if you are talking getting on paper at 1500 yards then I could concede and say you are right, it is meaningless. For 700-800 yards, it is anything but meaningless.

Michael:
The point is that my methods, Bryans methods, and every body elses methods are going to be different and in different circumstances. There is no way we are all going to match.

JonA:
But they should, if we're all doing it right. Unless there's something wrong with a rifle/bullet combination used by one of the people measuring, if they all do it right they should all get the same answer (within a certain amount of variability).

No they should not match. If I use a 308 win to test a 210 VLD with a 24" 10 twist barrel using top velocity capabilities and you test the same bullet from a 30-378 11x 30" barrel using top velocity capabilities, the difference is going to be QUITE noticable. The only time they should be close is if different shooters are using similar velocities, similar stabilty factors, and similar bore qualities. If and that is a big if, various shooters are using the same types of set ups, then you are right, numbers should be very close to eachother provided they are doing it right. Unfortunately, most shooters have different equipment. This is why I dont use anybody's BC figures. I find them myself for MY equipment. If I dont have time to figure it out, I may use a published or otherwise accepted value to get on paper.

Michael:
I would suggest that Wild Cat bullets at least fire over double chronies and the numbers will speak for themselves.

JonA:
He did. And it matched Bryan's numbers almost exactly.

Then what is the problem here?

 

[Jon A]

Like hell it is meaningless. Use what ever method you like to determine a BC. The proof of accuracy is where the bullet hits the target.

Now if you are talking getting on paper at 1500 yards then I could concede and say you are right, it is meaningless. For 700-800 yards, it is anything but meaningless.

In the weather I've mainly tested in the past, the difference in drop at 750 from a 300 yd zero between a .75 BC bullet and a .800 BC bullet when launched at 3200 fps is only a bit over one inch. I don't know what sort of group sizes you're shooting at that range or if you're shooting 10 or 20 shot groups to decipher the fractions of an inch difference you'd get from an error in measurement, but the point is when the variability of your measuring methods greatly exceeds the variability of the value you're trying to measure, you need new methods.

No they should not match. If I use a 308 win to test a 210 VLD with a 24" 10 twist barrel using top velocity capabilities and you test the same bullet from a 30-378 11x 30" barrel using top velocity capabilities, the difference is going to be QUITE noticable.

Acutally, if you use G7 BC's they should be right in the same ballpark. Why do you insist on using G1 BC's when you know they are so velocity dependent for these bullets?

Then what is the problem here?

An error when converting the data in JBM made it look like they didn't match at first, but they did upon re-entry by others.

 

[Michael Eichele]

In the weather I run them in at the velocities I run them using your example of a .75 versus a .8 is more like 3". That said, most of my loads dont sport BC's that high (with the exception of my Edge). With average bullets running .around .500 and changing them by 0.050, the margin is huge. Like 8-9" huge. I am sure that you can see 8-9". Using my 208 AMAX load comparing .648 versus even a small amount like .625, the error is about 2.5". This is more than enough to notice if things are running high or low. If you cant notice that, dont hold it against me for being able to do so. In addition, the degree of accuracy of both of my primary rifles is better than average. When they consistently throw down groups in the .4 MOA bracket and sometimes less at 1/2 mile on a windless day, I get a pretty good idea of what my BC's are when on multiple days I can predict where the are going to be. I am sure you know when your groups are low or high even when they are in the 10 ring or X ring for that matter. The way I see it, groups that are consistently low even by an inch or two are noticable. Unfortunately, most scopes are not fine enough to adjust that out. Thank Goodness we have math to at least take the lows and highs and add them to the equasions for BC purposes among others.

All I will say is my methods are working for me. I have no intentions of looking for a new method. When I start scratching my head or start missing shots that are unexplained, I will look for a new method. Or when I can afford doppler radar whichever comes first. Untill then, double chronies and drop tests will have to work. IMHO those are not too bad a way to figure out how to kill a small target at 1/2 mile. G1 or G7.

Other than that, we will agree on some things here and will have to respectfully agree to disagree on the others.

Regards!

M

 

[LR3]

I have a question for the experts , why does the same 350smk from two different 375 rifles have different Bcs although the velocities and twists (12 and 10) are different?

 

[Ridge Runner]

does having the same exact number matter most? or is the main thing to hit where ya aim?
I use the following BC's to hit where I'm holding
160 nosler accubond .62
140 berger vld .7
200 wildcat .88
are they right? don't matter its what works in my rifles, under my conditions
RR

 

[Michael Eichele]

I have a question for the experts , why does the same 350smk from two different 375 rifles have different Bcs although the velocities and twists (12 and 10) are different?

The fact that I am responding does not mean I am an expert. Take this with a grain of salt.

1: BC's change with velocity.

2: Different twists make for different stability factors. Stability factors can at times play a role in BC's.

M

 

[elkaholic]

I have a question for the experts , why does the same 350smk from two different 375 rifles have different Bcs although the velocities and twists (12 and 10) are different?

They have a different b.c. "BECAUSE" the twists and velocities are different. The same bullet traveling at different speeds will exhibit a different b.c. Twist also affects it to a lesser degree....Rich.......I AM NOT AN EXPERT

 

[eddybo]

does having the same exact number matter most? or is the main thing to hit where ya aim?
I use the following BC's to hit where I'm holding
160 nosler accubond .62
140 berger vld .7
200 wildcat .88
are they right? don't matter its what works in my rifles, under my conditions
RR

AMEN hell with the experts say the BC is, only thing that matters is what plugs into my calculator to give me hits.

 

[groper]

G1 BC`s change DRAMATICALLY with velocity...

G7 BC`s change very little with velocity over the entire flight regime in which we are interested in, for the VLD bullets we are interested in.

BC`s dont change with environmental conditions.

BC`s dont change from one rifle to another. - caveat - the different rifling engraving marks on the bullet from different twist barrels and no of lands etc would effect the BC ever so slightly... however this effect is VERY small and would be extremely difficult to detect/measure/notice any difference - so its simply ignored and rightly so.

If you have a BC and velocity that is different from an accurately derived average BC by someone like Bryan Litz etc. AND you getting close to the mark with your doping, then you have adjusted your other variables such as velocity, bore ht, zero, environmentals etc. - in order to get there. These error-some adjustments you have now included in your trajectory calculation, means you WILL have significant trajectory errors at some point in your trajectory - it just might be much further down range than you normally shoot which is why you havnt noticed the problem... - which is WHY GETTING THE BC RIGHT IS SO IMPORTANT.

Which is why Bryan Litz has gone to all this trouble for us.

Which is why we should only use accurate BC`s users can trust in order to make an ethical LRH shot.

Which is why we should all be using the same BC, for the same bullet.

EDIT: I guarantee you will have a much better trajectory fit, over a larger portion of the trajectory, if you use a BC that bryan litz has published with your chronographed velocity (provided its working accuratey) You will then be able to find where your previous errors were, by changing the other variables such as bore ht, zero or environmentals etc in your ballistics calculator, to yeild grouping on the center x ring @ 1000yds.

 

[Michael Eichele]

deleted.........

 

[eddybo]

I dunno. I have used published BCs for several different bullets to shoot out to 1 mile. One bullet in particular, If I use BLs given BC I would hit nothing but air. If I use my "derived" BC I am very close. I dunno what the BC of the bullet is all I know is what I can plug in exbal and hit stuff.

With say a 7mm a-max at 300, 500, 800, 1200, 1400, and 1760 using the advertised BC I am pretty close with some slight anomalys which I can usually correct with a modification to the primary and secondary BC.
For one bullet I plug in my derived BC and it works just about as well as the advertised BC for other bullets.....I plug in Bryan's BC for that same bullet not even close.

Who is wrong I dunno, do not care anymore, and will admit that the error is probably with me. I wasted close to 70 rounds of barrel life of my 338AM trying to find what the problem is. I finally threw my hands in the air, plugged in the number that works and have not looked back. If I start a new profile in exbal for this bullet using the same exact data except for BLs BC and my "derived" BC there is a substantial difference.

There is one simple explanation why it could be that most advertised BCs work and my "inflated" "derived" BC also work. That explanation would be that all advertised BCs are grossly over inflated. Maybe they are grossly inflated so they will actually work?

I cannot recal the exact numbers Kirby was using to shoot stuff way out there with the 7mm AM, but am pretty sure that it is higher than BLs BC of the bullet. I think if I had one shot at a target at 1400 yards and the opportunity to use either whatever BC Kirby was using, or the new corrected BC for the 7mm 200gr wildcat , I would not have a problem choosing which I would use.
I have decided that BCs do not matter and are irrelevant. The only way to get it right is to shoot the rifle at multiple yardages further than you will ever shoot at an animal and creat a BC. Take no shortcuts,and have no problems.

 

[Michael Eichele]

I dunno. I have used published BCs for several different bullets to shoot out to 1 mile. One bullet in particular, If I use BLs given BC I would hit nothing but air. If I use my "derived" BC I am very close. I dunno what the BC of the bullet is all I know is what I can plug in exbal and hit stuff.

With say a 7mm a-max at 300, 500, 800, 1200, 1400, and 1760 using the advertised BC I am pretty close with some slight anomalys which I can usually correct with a modification to the primary and secondary BC.
For one bullet I plug in my derived BC and it works just about as well as the advertised BC for other bullets.....I plug in Bryan's BC for that same bullet not even close.

Who is wrong I dunno, do not care anymore, and will admit that the error is probably with me. I wasted close to 70 rounds of barrel life of my 338AM trying to find what the problem is. I finally threw my hands in the air, plugged in the number that works and have not looked back. If I start a new profile in exbal for this bullet using the same exact data except for BLs BC and my "derived" BC there is a substantial difference.

There is one simple explanation why it could be that most advertised BCs work and my "inflated" "derived" BC also work. That explanation would be that all advertised BCs are grossly over inflated. Maybe they are grossly inflated so they will actually work?

I cannot recal the exact numbers Kirby was using to shoot stuff way out there with the 7mm AM, but am pretty sure that it is higher than BLs BC of the bullet. I think if I had one shot at a target at 1400 yards and the opportunity to use either whatever BC Kirby was using, or the new corrected BC for the 7mm 200gr wildcat , I would not have a problem choosing which I would use.
I have decided that BCs do not matter and are irrelevant. The only way to get it right is to shoot the rifle at multiple yardages further than you will ever shoot at an animal and creat a BC. Take no shortcuts,and have no problems.