Let's argue about BC's

[eddybo]

Hilarious!!! next time ill be sure to listen when your stirring the pot so the garbage sinks in shall I?

Almost as funny as this - the highlight of the thread - in case anyone missed it... Hysterical and painfully accurate...



I think ive found a new sig...

Groper

You still wanna play I see, or maybe I just get a ahole vibe from your posts that is not really there. Your the kinda guy guy who likes to slap people with the extended olive branch. You will find that I actually have very little ego when it comes to longrange hunting or internet forums, and that I admit when I am wrong very readily, usually. I am wrong on occassion and understand that I am not perfect.

That is okay, BLs quote is actually pretty accurate and he has stated something similar to me before, only in a less candid manner. I see you have gone back and reread some of the posts, did you see any hints, I was throwing you as to the stepped BCs. I gather that you are proficient with G7 BCs, but I cannot get a sense for your experiance with G1 BCs. If you have never stepped BCs or had problems with G1 BCs I am assuming very little.

BTW here is more ammunition for you, now that you are listening, just so you will realize how stupid I actually am. I can enter that .89 BC into a ballistics program and by just a few adjustments "errors" make that BC work out to 1000 yards with little enough error that I would shoot at an animal using it to that range so long as I get a chance to shoot in the actual conditions I would be hunting in. Which I always do anyway. I am ignorant enough that I could not even figure out why it worked, still cannot, other than the fact that the velocity BL used to calculate BC does not even come into play until past 600 yards. Best guess my second BC comes into play a little quicker. Even I understand that even though G1 BCs accuracy are dependant on velocity to some extent, but probably not even close to the extent that mine errs.

It was not until I started shooting to a mile more regularly and past that on the occassion where I got a chance to shoot further, to realize that that it was even a problem other than being "incorrect." After realizing what a problem it is for shooting ULR I started doing more shootiing.

I did find some scope errors at that point, by measuring distances between groups on targets. I also had a slight scope height error. I have never done a 100 MOA box chart, but probably will, out of curiosity, even though I have never dialed more than 60 MOA. (Actually the scope on the rifle now was used on another rifle that wokred very well, and matches very closely with the results from the first scope, maybe they are both broke) I found that my efforts to minimize errors at long range where masking some of the errors. Duhh that is what they are for.

I did find some other problems such as my 800 yard target is 787 and my 600 yard target is actually 610 and that the target I use as a 450 yard target is actually 465. (yea I had a crappy range finder when I set those targets) I factored in the decline in my range which is very slightly downhill but then rises back up. With each error found I thought finally eureka I can now use the "correct BC" with each error I found. I spent more time over at the sopt where I can shoot out to a mile I adjusted the 8 to 10 yard ranging errors on those targets. Still to no avail.

I still cannot make it work with the correct "BC" yea stupid I know. I rebarreled the rifle because I felt that I was going to shoot out my barrel trying to figure it out, and to see if that had any effect. I actually saw insignificant or no changes when I changed the barrel. (although I do think that it can be a factor, just probably not in this case.)

Knowing this is physics I decided that I just had to make this right. I bought an ipod touch and a new ballistics program and promptly started all over again with new resolve, assuming that maybe the problem was with exbal or my PDA. I got similar results and pulled more of my hair out. I bought a home weather station, assuming the info I was getting from my kestral was the problem. I bought another swaro range finder to verify yardages to targets. I used other people's range finders to confirm the second rangefinder.

As things progressed I decided that if I could not make the real BC work I may as well use the time to make what I had work as well as possible while I tried to figure it out. That is when I started addding more steps to the BC to make it work even better. When I had to write the check to buy another batch of $1.65 per shot bullets I started questioning my sanity. If my drop chart works, and it does, and it works everywhere I have used it, which it has, why would I continue to bang my head against the wall. I will leave the science to you guys and continue to using my home grown methods learned from this site and from shooting. Go ahead tell me how impossible it is, I know, but it does work well enough.

Here is what I find stupidest about my actions with this rifle. I spent enough money trying to make a "correct" BC work that I could have bought another custom rifle. How is that for stupid in the supreme? If I could have billed my hourly rate that I charge at work for the time I played with this rifle trying to make it work, I could have bought a new truck. If I were not still sick at home I would not even be posting about the dang thing as it just adds to moments of my life wasted. I wasted all that money trying to make a number derived in another rifle at another velocity in another state at a different altitude work in my calculator. I am actually ashamed of the depth of my stupidty.

As I have stated again and again, I am sure that there is an error somewhere, and I am sure that it is probaly my error. It is just one I cannot recreate in any of the other rifles that I shoot, to nearly anywhere this degree. At this point it does not bother me anymore, I have accepted that I have a very repeatable error in this rifle, but not repeatible in any others that I own or have built. Meaning I cannot just draw a BC out of the air for any rifle and make it work with this degree of accuracy.

No need to respond, most of what yall say is over my head anyway, cause I really am DUMB. But even stupid people like to shoot long range and with a little work can be proficient at it.

You were lying when you stated you did not get a chance to long range hunt right? I thought you were from Australia, and just assumed you were blowing smoke. If it is true that you do not get to hunt long range I am sorry for my comments about that.

 

[Michael Eichele]

The thing is, I've never heard any credible explanation of exactly how a particular barrel can add to a bullet's BC beyond its potential (I don't really think "static" is a good word for it) by any significant amount.

Everybody acknowledges if there is something less than optimum with a barrel/bullet combination that can lower the observed BC. It's claims that a particular barrel can somehow make a bullet fly significantly better than its physical shape and mass should allow that raise eyebrows.

You use 'observed' I use static and dynamic. I think 'observed' is a poor word you think static is a poor word. I guess that makes us even. (No dissrespect meant).

If a given bullet arrives at a target at a given TOF and velocity that is the 'observed' or 'dynamic' BC. When it is drawn out on paper and mathematically examined, that is the 'static' BC (SD/FF). I get the impression here that when Bryan does a TOF test that the BC value determined is an absolute (unobserved) value. When I test a BC and it's TOF is different, it is now an 'observed' BC which is invalid. The reality is that Bryan's or anybodies tests for that matter yeild 'observed' BC's. It is this BC that is 'observed' from my rifle that I am concerned with. I could care less about it when it is drawn out on a peice of paper or generated by a computer.

Static versus dynamic are great words. There will be a calculated BC and an observed BC, a static BC and a dynamic BC. Rarely will they ever agree down range.

Is it possible to change the sectional density of a bullet with a tight bore? Yes. Will a higher SD 'add' to a BC? Yes.

Are we splitting hairs here? Sure. The point is, to SOME extent we are both right. The truth lays somewhere in the middle.

You have to understand that for the most part, I agree with you and Bryan and Mark that BC's are typically reduced by a barrels influences. I just happen to believe that a given barrel can maximize a bullets potential as well, and in some circumstances, (for technicality sake) add a fraction. Either way, the sum of the parts working together make up the 'dynamic' (observed) BC that will cause a given bullet to arrive at a given range with a given TOF and a given velocity be it higher or lower than yours. That is the only value I care about. If you say bullet xyz should only have a .568 BC and my real TOF and end velocity show .543 or heaven forbid, .585, guess which one I am going to use?

I think maybe you guys are under the impression that I believe that if a bullet has a potential of .6 (in general) that I believe that a barrel's influence and other potions can make it have a .8 BC and that is not the case. So far, I have only seen one example where the 'observed' BC was about .060 higher than it should have been which should be verified or debunked next week. I dont feel however that the difference between .500 +/- .025 should raise any eyebrows or hackles.

What I am refering to here and have been refering to is the fact that anybody can come up with a value that is lower or higher when compared to a BC that has been tested by another indavidual. I dont meen come up with a BC that is physically impossible, I meen a BC that is higher than the bullet it was compared against (ie your bullet from your rifle versus my bullet in my rifle versus Bryan's bullet in his rifle.) Many here would all like to accept one or two people here as the final authority on ballistics. The final authority here really is the ballistics in and of themselves.
M

 

[RockyMtnMT]

I agree...but does that have anything to do with the BC of the bullet? If you shoot a 180 E-tip out of your 30-338 LM and compare the "flight orientation" to the 180 E-tip out of my 300 WSM, does that change the drag coefficient of the bullet?

Let's take it a step farther... suppose you shot that bullet out of your 30-338 in a 28" 10 twist Lilja and I shot it out of a30-338 LM 26" 11 twist 5C Broughton. Would it change the BC (drag coefficient) of the bullet? No... the bulet's BC is the same... according to the defintion of shape and mass.

These things definately do not change any other data. One must change the bc in order to change the poi. It does not change the physical characteristics of the bullet that is sitting still. But the in flight drag characteristics will certainly be different depending on how that bullet orients in flight. Not the bullets fault.

Yes... and if it doesn't fly perfecly, does that change it's BC? I say no. the BC must be accurately represented and the flight imperfection applied.

If this is the case, then tell me what do I input into the ballistic program other than the bc (assuming all other inputs are correct). Who is to say that the bc test barrel is giving perfect flight characteristics. Maybe yours gives better results than the testers. Do you scramble to change some other input in order to get the right results.


Nahh, you're throwing oranges into the apple bushel. When you flip flop the nose and tail you have CHANGED the SHAPE of the bullet... right? Right.

That is the point. The form of the bullet has not changed if it is flying backward or sideways. The bc is the bc. I have exaggerated this in order to make a point. We know that a little slower twist is better for long range but does not work as well for short range. This is because of what the rpms do to the orientation of the bullet in flight. Thus changing how the atmosphere encounters the bullet in flight. Thus changing how much drag is imparted onto the bullet changing how fast it slows down. Now you must change the bc input to accommodate the different drag. Inexact twist rate (button rifled) and varying muzzle velocities will have direct effect on the rpm of the bullet.

On Litz being the "one and only" BC source, vs "pilot error"... I have already said that I don't think BL is infallable.... and having said, that who would you say has more knowledge and experience in the subject.... at least in these forums? Supose I made a post here claiming that the 180 E-Tip had a BC of .612 and BL said it was .543 ... Which BC would you use as a starting point?

You said it, STARTING POINT. Not constant only point.




I think the obvious is to make sure all the inputs are as accurate as possible.... garbage in, garbage out. It becomes subjective at some point.... which inputs do you trust most? Then you can run multiple options and see which one fits best.

We have to look at all the data and make the best decision we can with the information we have. None of it is magic or hocus pocus, but the fact is we have no way of ever knowing exactly what our bullet is doing in flight.

We could just do what someone said earlier in the thread. Just keep changing barrels until we find a hummer. I don't know about you, but not likely for me.


To be honest with you that's what I've done in my limited experience . Too many variables? I don't think so. Long shots are accurately predictable. That's been proven.

We learn how to predict the variables even if we do not know exactly what they are by shooting.

Steve

 

[Buffalobob]

Pretty much everything Bryan has said I can mostly agree with and pretty much live with.

For Courtney to say I have to have a lot a fancy equipment out find out a bullet BC only tells me he never walked into a quantum mechanics final exam armed with a bamboo slide rule. I also question exactly how many courses he has taken in numerical analysis. A lot of science went on before the game boy generation invented computers. One of the great debates of my education was on the merits of the bamboo versus plastic slide rules and whether Deitzen was the best.

 

[rscott5028]

With all of the hair splitting, one thing I find lacking is adequate attention paid to statistics.

We already know match bullets are not perfect and some use meplat trimmers at the detriment of BC in order to gain consistency. Who here is good enough to evaluate the meplat under a microscope and calculate the adjusted BC for the amount of deformation? Heck, I can see differences in meplat with my tired old eyes. Am I to assume that the ogive and boat tail are perfect for every bullet? (I think MC and BL already acknowledged differences among bullets and Lot #'s.)

Hence, you can never know the "real/actual/precise" BC of an individual bullet until it is measured upon firing. Once fired, you can never repeat that test with the same bullet. So, we're really talking about using samples to estimate the BC of future bullets fired.

While some advocate that the shape of a fired bullet has not changed because they retrieved the bullet and measured the dimensions. I challenge them to reload that same bullet and fire it again with the same measured BC. (And, I don't think they intended for that to be the case anyway.)

I'm still eager to read the complete published works by BL, MC, Sierra and others. But, I sense they are simplifying things for us to talk about a % change in BC from this or that barrel. When we really should be concerned with statistical outliers. ...something they hinted at...

...extraordinary claims require extraordinary evidence to back them up.

Statistically speaking, there are averages (mean), standard deviations, and distributions associated with these experiments. Their std dev is likely to be much less than mine due to the precision of their measuring and ability to control the variables.

If I fire a few shots and measure a different BC, that's exactly what I've done and my observed data is irrefutable. Nonetheless, the source of the differences may not be accounted for as already discussed. And furthermore, the data alone does little to give a high degree of statistical credence, as in a 2 tailed T test with 95% or 99% confidence level, to my assertion that my BC is different from theirs.

In fact, I may have to shoot a 3rd of a box of bullets (random samples from the whole Lot #) before I can statistically project the BC for that Lot.

Fortunately, match bullets are pretty good quality and the std dev is likely to be very low (certainly better than my own shooting equipment and ability). As such, I'm pretty comfortable using BL's published BCs and I vow to do a better job identifying any discrepancies before I publicly flame the guy.

BTW Bryan - You misspelled "very"

If your bullet dimensions very a lot from what I tested, it's a legitimate reason why you would find a different BC for that bullet.

...should be "vary"

But, we can debate that in another thread. ;-)

-- richard

 

[BryanLitz]

BTW Bryan - You misspelled "very"

Out of aaaalllllll those words, I only mis-spelled one !?!?!?!

I'm awesome!!!

BTW, You make a good point about statistics.

 

[edge]

"There are three kinds of lies: lies, damned lies and statistics."
- Autobiography of Mark Twain

 

[groper]

You use 'observed' I use static and dynamic. I think 'observed' is a poor word you think static is a poor word. I guess that makes us even. (No dissrespect meant).

If a given bullet arrives at a target at a given TOF and velocity that is the 'observed' or 'dynamic' BC. When it is drawn out on paper and mathematically examined, that is the 'static' BC (SD/FF). I get the impression here that when Bryan does a TOF test that the BC value determined is an absolute (unobserved) value. When I test a BC and it's TOF is different, it is now an 'observed' BC which is invalid. The reality is that Bryan's or anybodies tests for that matter yeild 'observed' BC's. It is this BC that is 'observed' from my rifle that I am concerned with. I could care less about it when it is drawn out on a peice of paper or generated by a computer.

Static versus dynamic are great words. There will be a calculated BC and an observed BC, a static BC and a dynamic BC. Rarely will they ever agree down range.

Is it possible to change the sectional density of a bullet with a tight bore? Yes. Will a higher SD 'add' to a BC? Yes.

Are we splitting hairs here? Sure. The point is, to SOME extent we are both right. The truth lays somewhere in the middle.

You have to understand that for the most part, I agree with you and Bryan and Mark that BC's are typically reduced by a barrels influences. I just happen to believe that a given barrel can maximize a bullets potential as well, and in some circumstances, (for technicality sake) add a fraction. Either way, the sum of the parts working together make up the 'dynamic' (observed) BC that will cause a given bullet to arrive at a given range with a given TOF and a given velocity be it higher or lower than yours. That is the only value I care about. If you say bullet xyz should only have a .568 BC and my real TOF and end velocity show .543 or heaven forbid, .585, guess which one I am going to use?

I think maybe you guys are under the impression that I believe that if a bullet has a potential of .6 (in general) that I believe that a barrel's influence and other potions can make it have a .8 BC and that is not the case. So far, I have only seen one example where the 'observed' BC was about .060 higher than it should have been which should be verified or debunked next week. I dont feel however that the difference between .500 +/- .025 should raise any eyebrows or hackles.

What I am refering to here and have been refering to is the fact that anybody can come up with a value that is lower or higher when compared to a BC that has been tested by another indavidual. I dont meen come up with a BC that is physically impossible, I meen a BC that is higher than the bullet it was compared against (ie your bullet from your rifle versus my bullet in my rifle versus Bryan's bullet in his rifle.) Many here would all like to accept one or two people here as the final authority on ballistics. The final authority here really is the ballistics in and of themselves.
M

You might notice the increased SD by shooting a 30cal bullet thru a 243 barrel... send some to eddy, he might try actually try it... but how much tighter bore do you think it would take to make a noticeable difference michael? im sure you capable of calculating the area of 2 different circles, so you should be able work out exactly what difference a barrel thats .0005 smaller in dia will produce...

lets truce, all the info is covered, nothing more to add...

 

[Michael Eichele]

You might notice the increased SD by shooting a 30cal bullet thru a 243 barrel... send some to eddy, he might try actually try it... but how much tighter bore do you think it would take to make a noticeable difference michael? im sure you capable of calculating the area of 2 different circles, so you should be able work out exactly what difference a barrel thats .0005 smaller in dia will produce...

lets truce, all the info is covered, nothing more to add...

No, lets keep it going....I am still learning here! That said, I agree that this dead horse has been beaten pretty flat.

You know, I did admit it was splitting hairs. Some barrels known as tight bore barrels have a full .001. Sure it only equals .002-.005 gain to the BC, but it illustrates that a change can and will occur.

Truce? We were never at war. Only sharing thoughts. Please visit the link below: If we were at war in your eyes, then yes, truce.

http://www.longrangehunting.com/forums/f19/jon-groper-litz-mark-topshot-courtney-etc-post-you-68814/

 

[MontanaRifleman]

No, lets keep it going....I am still learning here! That said, I agree that this dead horse has been beaten pretty flat.

You know, I did admit it was splitting hairs. Some barrels known as tight bore barrels have a full .001. Sure it only equals .002-.005 gain to the BC, but it illustrates that a change can and will occur.

Truce? We were never at war. Only sharing thoughts. Please visit the link below: If we were at war in your eyes, then yes, truce.

http://www.longrangehunting.com/forums/f19/jon-groper-litz-mark-topshot-courtney-etc-post-you-68814/

Ya know, I'm not sure how many times I've used the word "sigificant" but it's been a bunch. I'll freely admit that there will be be some minor variation in bullets and that one bore might be .001 tighter than another bore but that these things will not make a signifacant difference in BC anywhere near what Paul originally came up with (.9 vs .74) and some others seemed to have confirmed in their own experiences. I would subjectively consider 5% deviation to be fairly significant, 10% very signicifant, and 15% HUGE.

 

[MontanaRifleman]

Pretty much everything Bryan has said I can mostly agree with and pretty much live with.

I pretty much do too

 

[MontanaRifleman]

The thing I learned and really, really liked most about this thread is that when my GS HV 177's get here I can pretty much make them any BC I want them to be... hmmmm... .8'ish sound real nice

gun)

BTW Michael, got an email the other day, they are being made and I should get them sooner than expected.

any luck with you?

 

[Buffalobob]

Montanarifleman

You asked a question and I have been repairing a 1936 Crane Dial Eze for the last three days so my attention wanders to why 40 psi needs tight nuts over good washers. It is at least as nasty of a job as finding a bullet BC.

So here is the process I used to come up with an allowable 13 % erro in BC with my stuff where I hunt in Wyoming.

Here is what I did.
If one assumes that an antelope has a kill zone of one MOA at 1000 yards then we can make some simple calculations concerning BC error. I used my antelope because it just happened to be a really high but fatal strike and I wished to prove that there is a reality to long range hunting and that if you have a very good rifle and are reasonably competent there is a lot of slop/error that can be tolerated.

Take your favorite combination of bullet and rifle and your favorite ballistics calculator and enter the conditions which usually exist when hunting antelope. Runs those for 1000 yards and record the drop and the BC that you used. Then keeping all conditions the same increase (or decrease) your BC until you have your bullet striking exactly one MOA different at 1000 yards. Then compare the starting BC with the ending BC. That is the percent error allowable in BC.

If you really want to see some big numbers assume you are shooting at an elk and use a 2 MOA kill zone and see what your BC error can be.

Obviously if you favorite rifle is a 30-30 you will have used up all of your error at 1000 yards before you even load it. This brings us full circle to the reason Kirby developed the Allen Mags. So sloppy people like me could make spectacular looking shots at long range. Lots and lots of speed combined with high BC covers up a lot of mistakes.

 

[eddybo]

You might notice the increased SD by shooting a 30cal bullet thru a 243 barrel... send some to eddy, he might try actually try it... but how much tighter bore do you think it would take to make a noticeable difference michael? im sure you capable of calculating the area of 2 different circles, so you should be able work out exactly what difference a barrel thats .0005 smaller in dia will produce...

lets truce, all the info is covered, nothing more to add...

Love the sig, and do wish you the best with the bullet. I would maybe try a 7mm through a 270 It would be according to how my meds are regulated. Today, I might.