Let's argue about BC's

Sorry Steve,
Your point is well taken.
I was more or less making rhetorical reference to Michael Courtney's statement...
We have seen significant variances in BCs between different rifles, and even within the same rifle before and after polishing the bore. Lots of factors effect bullet drag.
thanks!
Richard
 
When you say you have seen significant BC variances, can you provide us with more detail? What was the accuracy of your overall BC tests and what was a significant variation? 1%? 15%? I think everyone agrees that there is always some BC variation (1%), the disagreement is over how large the G7 BC variation can be by the same bullet fired in different rifles, different velocities, etc.

Bullet 125 NBT

Rifle/Cartridge Near V (fps) G7BC/uncertainty G1BC/uncertainty

TC Encore/30-30 2245 0.153/0.003 0.306/0.005
Rem 700/.308 2794 0.153/0.005 0.308/0.010
Rem 700/.30-06 3010 0.158/0.005 0.319/0.011
Rem 700/.300 WM 3008 0.141/0.002 0.283/0.004

The table above shows our measured BCs (two chronograph method) for the Nosler 125 grain ballistic tip from four different rifles. The measurements from the first three rifles are very close and the differences are well within the uncertainties and expectations from the muzzle velocity differences. In contrast, the BC measurement from the .300 Win Mag is 11% lower than the .30-06 in spite of being fired with very nearly the same muzzle velocity. The 11% difference is significant since the uncertainties in BC for the different rifles are 1-3%. We've measured lower BCs in this rifle for every bullet we've tested in it.

Michael
 
Bullet 125 NBT

Rifle/Cartridge Near V (fps) G7BC/uncertainty G1BC/uncertainty

TC Encore/30-30 2245 0.153/0.003 0.306/0.005
Rem 700/.308 2794 0.153/0.005 0.308/0.010
Rem 700/.30-06 3010 0.158/0.005 0.319/0.011
Rem 700/.300 WM 3008 0.141/0.002 0.283/0.004
That's very interesting stuff. It makes me wonder if perhaps the 300 WM has a poorly cut crown or other flaw that kicks the base of the bullets sideways a bit upon exit. Have you tried measuring at longer range to see if the difference stays at distance?

It actually surprises me that bullet keeps such a constant G7 at different velocities (in the other three measurements) because it isn't really a VLD shape.
 
Won't make that mistake again.

Hopefully Groper learned the same lesson and won't be lecturing us anymore about how barrels don't affect BC. Over the last five years I have moved from one end to the other end of the spectrum and back again on the barrel issue. But that is the good thing about this forum, always some new stuff to learn and digest and try out.

I have grown so weary of shooting animals at 1K that I have turned to bows and pistols. The only rifle challenge left is 1500 to 2K and if Litz's BC work out that is great with me. Although I suspect that Broz has it right and you just got to spend the $5K for an exact distance rangefinder or have good terrain to range in.

My applications are in for this Fall and we will see who is still running their mouth and who is posting up videos of dead animals. :D

At the moment the only active members who are over 1500 yards on big game are the combos of Judd/Kevin and Shawn/JR, unless I have forgotten someone.
 
Bob and Eddy,
You keep going on about your success in taking game at long range, and therefore this must prove that your methods are sound... I see it more appropriately as "close enough" to get the job done.

I have little doubt that you have made successful big game kills at +1000yds, it doesnt surprise me, nor does it impress me. - I know what it takes to deliver a cold bore shot at 1000yds - and being able to hit the relatively large vital zone of a large animal at this distance is hardly a challenge for a knowledgeable long range shooter with precision equipment, and armed with an accurate trajectory prediction, in all but the most difficult wind conditions...

See, this is how a gambler operates - they always tell you how much money they won last week, but never how much they lost the week before....So i ask you, for every big game animal youve harvested cleanly at +1000yds, how many shots have you missed and/or wounded at +1000yds? You dont need to answer this question, but if you dont include the answer and truthfully with your responses, then theres no point bragging about your successes as a basis for "your methods must be sound". Obviously, if you shoot at enough animals, eventually your going to kill some no matter how far away they are...

I dont get the opportunity to hunt at long range where i live, so i cannot give you a killing comparison, however i regularly make cold bore shots on milk bottles at varying distances in excess of 1000yds, and if you could witness my success rate, im sure you would agree i should have no problem killing an animal should i be presented the opportunity... I beleive this is not due to my extremely talented shooting skill, but rather that i have built a very accurate trajectory for my rifles, based around Bryans G7 BC coefficients which ive proven to myself, work better than any of my best efforts at deriving BC`s from drop, and then building a trajectory from it. I know this, because if i setup the shot (tell them required elevation and windage) even my buddies with no long range shooting experience whatsoever, can point, shoot and hit the same impressive cold bore shots... To me, this proves accurate information is more important than experience...
 
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This has been an interesting thread and I am intrigued by the different reasoning going on here.

I really don't want to offend anyone or get into a ****ing match. I would genuinely like to understand some of your reasoning for what you "believe" about this subject.

I'm especially interested in why some of you believe that a bullet's BC is affected by what rifle it may be shot from? What is it that makes you think this? Is it some sort of mojo, or does the rifle actually change the form and/or mass of the bullet? I'm really not being sarcastic here, I just don't get it? I would really like to know why you think this.

A bullet's BC (drag coefficient) is based on it's shape and SD... period... is it not? And there are different drag models for different shapes... do we agree?

This is not new science by any stretch of the imagination. These principles have been used from small arms to artillery for many years. Navy ships can throw really big projectiles for miles very accurately and they don't have a different drop chart for each gun.

Why is that you think the bullets BC is changed by a particular rifle just because you get different results shooting from different rifles? Why is it that you don't think that there might be some discrepancy in the equipment rather than the proven science? I honestly would like to know.

I admit that I have only done a little BC testing under very crude circumstances and the G1 BC curve didn't quite fit... not surprising since I was using G7 bullets. Never-the-less, if I had done the same testing as some of you and got your results which differed from Bryan Litz, I would be questioning my testing much more than his based on FACTS that I have already spelled out very clearly in this thread.

This really isn't a flame... it's a straight forward point of discussion. I am just very confused by the reasoning here, and looking for answers. Maybe you can convince me, but so far you haven't... you haven't explained how a bullet's BC is changed from one rifle to the next and that is exactly what you need to do. You must demonstrate how a bullet's shape and/or mass is changed from one rifle to another or else you are lost. This IS science and not mojo. The laws of physics have never been bent.... not even just a little... unless you are Jesus and can walk on water.

BTW, please don't assume that I will just shoot at criters 1500 yds away (unless they are are wolves or other vermin) without first shooting my rifle to that distance. If I come up with discrepencies and fail to learn the cause, I will adjust (fudge) to make my shots good.
 
Montanarifleman,

Did you read Bryan's link? He explained the different barrel to some degree. Yaw induced by the barrel will cause a difference in bc from one barrel to another. He did not address what I asked about as far as twist and stabilization factor induced yaw. But it only stands to reason that that would also cause a difference from rifle to rifle with the same bullet.

Steve
 
Does a clean car get better gas mileage?

Does a car with a misaligned front end get poorer gas mileage?

Do dimpled golf balls fly farther than smooth ones?

Does the Berger 338 Hybrid really deform from high velocity?

Does the barrel/rifling impart any change to the bullet's jacket?

It seems to me like the barrel might have some influence on the drag that the bullet experiences. I have no idea how much.

The shooter and ammo have a huge influence on POI. But, that's not the same as changing the BC.
 
I have never made a wounding shot on a long range game animal. I have missed, but due to innattention, as in forgetting to dial back to zero twice or maybe even three times, and once for entering inclination incorrectly. I did gutshot a yote because I had an incorrect range for the first shot. I held an additional 5 MOA based upon seeing my first bullet impact short. He died within sight but I still did not like it. I do not like to make an animal even a yote to suffer because of me. I have busted milk jugs cold bore much further than 1 K. I have not taken an elk past 1200, but if the opportunity presents itself this year I will.


I am sorry that you do not get to hunt long range, I feel sorry for you, maybe you should migrate. Maybe that is the difference between us. The only thing that you do when you flub a shot is miss a target. They do not run around for two days dragging a leg. I have seen this and it is not pretty.

I still have not heard anything about your experiance although I have asked a couple of times if I recall. I may be wrong but there is not way I am going back and rereading this thread. How many barrels have you burned up on dedicated long range rigs? How many rifles have you worked drop charts that will usually allow you to make even a 1 MOA cold bore shot at 1500 yards?

You fudge velocities to make G7 BCs work correctly for you, right? Maybe you get them "good enough" I think you must have some problems with your scope. Maybe you need to go remeasure something. Have you ever seen a G1 BC work 100% correctly? If that was all you had to work with, you may think a little differently of my methods.

I have one rifle that does not fit the norm in I cannot make "correct" BCs work for that rifle. I can however make it work, with very good sucess. I do however have a good number of rifles that do work relatively well without resorting to BC juggling. G7 is a relatively new thing to many of us, maybe I could make it "correct" and have it still work if I had a G7 BC to try, I dunno.

I have already stated that I agree the G7 form factor is best. I still think you have to shoot the rifle at the ranges you are going to be shooting. Do you disagree with that? I have stated in probably just about every post I have flung into this thread, that you have to shoot the gun. Being a non hunter maybe that is not important to you being that you do not have the opportunity to hunt.

Do you think it is okay for someone having the best equipment available rifle, optics, range finder, ballistic computer using a G7 BC to take a shot longer than the equipment they are using has ever been proven to be accurate (remember this is a hunting site although you are apparently not a long range hunter)? If you dissagree with that then I will continue posting it, otherwise ...whatever. BTW my longest shot on a game animal was on a whitetail deer the vitals are about the size of a pie plate, which is not all that big.

BTW I am in complete agreement that once the dialing is done that just about any monkey can squeeze the trigger. In fact that argument is the reason I quit posting any of my hunts on this site. I let a buddy shoot a cow elk at 1187 yards. It was a good shot in calm conditions. I got chewed out about it by a couple of guys so said to hades with it.



Bob and Eddy,
You keep going on about your success in taking game at long range, and therefore this must prove that your methods are sound... I see it more appropriately as "close enough" to get the job done.

I have little doubt that you have made successful big game kills at +1000yds, it doesnt surprise me, nor does it impress me. - I know what it takes to deliver a cold bore shot at 1000yds - and being able to hit the relatively large vital zone of a large animal at this distance is hardly a challenge for a knowledgeable long range shooter with precision equipment, and armed with an accurate trajectory prediction, in all but the most difficult wind conditions...

See, this is how a gambler operates - they always tell you how much money they won last week, but never how much they lost the week before....So i ask you, for every big game animal youve harvested cleanly at +1000yds, how many shots have you missed and/or wounded at +1000yds? You dont need to answer this question, but if you dont include the answer and truthfully with your responses, then theres no point bragging about your successes as a basis for "your methods must be sound". Obviously, if you shoot at enough animals, eventually your going to kill some no matter how far away they are...

I dont get the opportunity to hunt at long range where i live, so i cannot give you a killing comparison, however i regularly make cold bore shots on milk bottles at varying distances in excess of 1000yds, and if you could witness my success rate, im sure you would agree i should have no problem killing an animal should i be presented the opportunity... I beleive this is not due to my extremely talented shooting skill, but rather that i have built a very accurate trajectory for my rifles, based around Bryans G7 BC coefficients which ive proven to myself, work better than any of my best efforts at deriving BC`s from drop, and then building a trajectory from it. I know this, because if i setup the shot (tell them required elevation and windage) even my buddies with no long range shooting experience whatsoever, can point, shoot and hit the same impressive cold bore shots... To me, this proves accurate information is more important than experience...
 
If you throw a football in a spiral does it have a better BC than a wounded duck end over end throw? Do all barrels shooting the same bullet have equal stability factors? What if the test barrel used to determine BC had crappy stabilization compared to the rifle you are shooting? Would it make a difference? Probably not really that much, but enough to cause a low or high hit on an elk. And I do not mean that as a smart comment, I just do not use the little smiley things very much.

This has been an interesting thread and I am intrigued by the different reasoning going on here.

I really don't want to offend anyone or get into a ****ing match. I would genuinely like to understand some of your reasoning for what you "believe" about this subject.

I'm especially interested in why some of you believe that a bullet's BC is affected by what rifle it may be shot from? What is it that makes you think this? Is it some sort of mojo, or does the rifle actually change the form and/or mass of the bullet? I'm really not being sarcastic here, I just don't get it? I would really like to know why you think this.

A bullet's BC (drag coefficient) is based on it's shape and SD... period... is it not? And there are different drag models for different shapes... do we agree?

This is not new science by any stretch of the imagination. These principles have been used from small arms to artillery for many years. Navy ships can throw really big projectiles for miles very accurately and they don't have a different drop chart for each gun.

Why is that you think the bullets BC is changed by a particular rifle just because you get different results shooting from different rifles? Why is it that you don't think that there might be some discrepancy in the equipment rather than the proven science? I honestly would like to know.

I admit that I have only done a little BC testing under very crude circumstances and the G1 BC curve didn't quite fit... not surprising since I was using G7 bullets. Never-the-less, if I had done the same testing as some of you and got your results which differed from Bryan Litz, I would be questioning my testing much more than his based on FACTS that I have already spelled out very clearly in this thread.

This really isn't a flame... it's a straight forward point of discussion. I am just very confused by the reasoning here, and looking for answers. Maybe you can convince me, but so far you haven't... you haven't explained how a bullet's BC is changed from one rifle to the next and that is exactly what you need to do. You must demonstrate how a bullet's shape and/or mass is changed from one rifle to another or else you are lost. This IS science and not mojo. The laws of physics have never been bent.... not even just a little... unless you are Jesus and can walk on water.

BTW, please don't assume that I will just shoot at criters 1500 yds away (unless they are are wolves or other vermin) without first shooting my rifle to that distance. If I come up with discrepencies and fail to learn the cause, I will adjust (fudge) to make my shots good.
 
Wow. I can't believe I wasted so much of my valuable time for such a result. Won't make that mistake again.

Sorry should have stated it better. While I recall much of what has been stated in this thread, about the only thing I can attribute directly to you is scope values are important. I am sure that I remember more of what you stated, but there are a lot of new guys here that I do not know, the names kinda run together. Sorry if I hurt your feelers again.
 
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