Let's argue about BC's

[MontanaRifleman]

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

No Steve, I haven't... my bad. And that's exactly the science (reality) based explanation I am looking for. I will read it. Ironically, it comes from Bryan.

 

[MontanaRifleman]

Does a clean car get better gas mileage?

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

I might be slow, but I don't see the analogy or application

Do dimpled golf balls fly farther than smooth ones?

Yes they do, but golf balls represnt projectiles (bulets) not barrels

Does the Berger 338 Hybrid really deform from high velocity?

Reportedly it does, but that's not what we're talking about. We are taliking about bullets and rifles within their operation parameters. I ASSUME that the disenters are explianing expeiences with bullets that are not being deformed and i take for granted that BL does not publish data and results on same.

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

A legit question... that has already been asswered, which is, not to any significant difference. I have picked up a lot of fired bullets and other than damaged noses due to impact... not the rifle bore... they are identical to their original shape and mass... other than engraving marks which have no signifcant impact on their drag coefficient.

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

It basically has zero affect on the shape and mass of the bullet.

The shooter and ammo have a huge influence on POI. But, that's not the same as changing the BC.

Yes, the shooter may have an influence on POI as well as other factors. As for ammo we are discussing apples to apples and apples to oranges.

 

[MontanaRifleman]

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.

See above: Wounded ducks are not what we're talking about. We are talking perfect spiral vs perfect spiral from different QB's. Barrels don't have stability factors, they have twists. Bullet have BC's and required SF's depending on velocity, range and application. The SF is determind by the bullet's shape, mass, velocity, range and application. I suppose it always possble for a professional bullet test to use the wrong test barrel but how likely do you really think that is? Care to give me odds on it?

As for references to this be a hunting site and your experience in shooting animals at extened distance, it really doesn't have any more bearing to the subject of BC's, their reality and application, than someone smashing milk jugs at 1K. This is a discussion of BC's, not hunting. I don't mean this to be a smart comment either, any more than you... just straight up talk.

 

[groper]

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.

If you bothered to read bryans link, it addresses this very consideration, and exactly how much it amounts to... very little...

I dont need to defend myself against you Eddy, and ive already expressed my view about experience and accurate knowledge - which you agreed with - so i dont care how many barrels youve burned up in order to gain the level of understanding you have... Instead id like to offer a glimpse of what my contribution to long range shooting and hunting is going to look like in the very near future, before this summer... i have in front of me, some projectiles which i personally designed in 3D CAD and produced from sound aerodynamic science, which could very possibly have the highest ballistic coefficient in a projectile .50cal and under (inclusive) in the world today. I have not accurately tested the BC, as im still changing the designs constantly so theres little point until im finished... but rough indications from extreme range shooting, suggest that they are extremely slippery... Im not ready to release many details at this point, but heres a little taste from the early part of their development... The hunting versions are identical, except with a "barnes X style" hollow point that peels precisely into 3 equal size petals... And, yep they all stabilize from standard twist rate barrels despite their extreme length, something noone else has been able to do...

 

[eddybo]

Dude you ask lots of questions but won't answer many. Hey no problem, you are right you do not have to defend yourself to me......mostly because I am not attacking you. You asked I answered, no quid pro quo required nor did I really expect it. Why would I want to know how much experiance someone has before I listen to what they say, after all it is just targets that you shoot at. I do not really care how much experiance you have. After all who needs experiance when you got a G7 BC that is accurate to 1% just go sight in at 100 and your good to 2K. BTW I did read the article, did you see a quote about the possibility of two correct BCs? I found it interesting.

At least answer this one question for me. Have you ever gotten a rifle ready to shoot long range using a G1 BC? What would you adjust after fudging the velocity without matching your drops?

Some sure have sure gotten uptight on this site in the last couple years. The attitude does not compliment you, but I do like the bullet, hope that works for ya. Sorry if I hurt your feelers too. All I have done in this entire thread is state an opinion and answer questions about my crap and my experiance...... take a chill pill. Sorry if I do not use enough smileys for ya.

If you bothered to read bryans link, it addresses this very consideration, and exactly how much it amounts to... very little...

I dont need to defend myself against you Eddy, and ive already expressed my view about experience and accurate knowledge - which you agreed with - so i dont care how many barrels youve burned up in order to gain the level of understanding you have... Instead id like to offer a glimpse of what my contribution to long range shooting and hunting is going to look like in the very near future, before this summer... i have in front of me, some projectiles which i personally designed in 3D CAD and produced from sound aerodynamic science, which could very possibly have the highest ballistic coefficient in a projectile .50cal and under (inclusive) in the world today. I have not accurately tested the BC, as im still changing the designs constantly so theres little point until im finished... but rough indications from extreme range shooting, suggest that they are extremely slippery... Im not ready to release many details at this point, but heres a little taste from the early part of their development... The hunting versions are identical, except with a "barnes X style" hollow point that peels precisely into 3 equal size petals... And, yep they all stabilize from standard twist rate barrels despite their extreme length, something noone else has been able to do...

YouTube - long range shooting 2000 yards

 

[Buffalobob]

We are taliking about bullets and rifles within their operation parameters. I ASSUME that the disenters are explaining experiences with bullets that are not being deformed and i take for granted that BL does not publish data and results on same.

If you don't want your bullets deformed don't put them in your chamber. Its that simple. All barrels reshape the bullet to one degree or another. If you wish you can take a rifle a single raw bullet and a hammer and see if you can get a bullet to go down your barrel without using the hammer.

Some reading for you on this thread

Post #94

Goodgrouper kept records for one or more of his rifles as the barrel deteriorated and found that the BC degraded as well.

There are several other barrel factors that will affect the BC of a bullet and those of us who shoot the extreme distances particularly with the bullet under discussion are well aware of some of them.

Post #125

I can think of many scenarios that would cause a bullet to fly with more drag than it should (stability problems, rough/worn barrels, bullet deforming in the barrel, etc). However, there is no way a bullet flies with less than it's minimal drag.

Somewhere in this forum is a discussion by Kirby of the many different barrels he tried during the early stages of developing the 7AM and adapting it to the 200 grain wildcat bullet. What he found was when you had more that 25% IIRC of the bearing surface under compression you began affecting the bullet adversely.


My advice to you is to go ahead and build your 56.5-375 Ruger and shoot soft bullets in it such as the 140 Berger out to a mile and keep careful records of your drops for about 500 rounds. And every once in a while let it go 50 rounds without cleaning. Also every once in a while take a shot at an animal at a mile where it really matters if you land the first (and only) bullet correctly. You will learn many strange and interesting things.

 

[eddybo]

Extreme example, prompted by your previous statement something to the effect of you can see NO WAY that a barrel can effect BC. As to the hunting comments they were not directed to you and were in response to mostly direct questions by others. Sorry if they bother you. This place has really really gotten sensitive.

Instead of staying for the next step of the evolution of a thread spiraling downward, name calling which I am sure is to follow soon. I am going to part ways with this thread again. So long as nobody quotes me or asks any more questions I am outta here again.

See above: Wounded ducks are not what we're talking about. We are talking perfect spiral vs perfect spiral from different QB's. Barrels don't have stability factors, they have twists. Bullet have BC's and required SF's depending on velocity, range and application. The SF is determind by the bullet's shape, mass, velocity, range and application. I suppose it always possble for a professional bullet test to use the wrong test barrel but how likely do you really think that is? Care to give me odds on it?

As for references to this be a hunting site and your experience in shooting animals at extened distance, it really doesn't have any more bearing to the subject of BC's, their reality and application, than someone smashing milk jugs at 1K. This is a discussion of BC's, not hunting. I don't mean this to be a smart comment either, any more than you... just straight up talk.

 

[MontanaRifleman]

Extreme example, prompted by your previous statement something to the effect of you can see NO WAY that a barrel can effect BC. As to the hunting comments they were not directed to you and were in response to mostly direct questions by others. Sorry if they bother you. This place has really really gotten sensitive.

Instead of staying for the next step of the evolution of a thread spiraling downward, name calling which I am sure is to follow soon. I am going to part ways with this thread again. So long as nobody quotes me or asks any more questions I am outta here again.

Eddybo, first off, you haven't bothered me at all, you really haven't.... why should I have been bothered? I don't take any of this personally and I hope you don't either. Internet debates can sometimes come across negatively on a personal level and sometimes folks do get personal, but believe me, i have not taken or given anything personal in this thread. Ant that is why i use smileys... and I'm still smiling When you posted that thread on the long range elk shots with you and your buds, and got some heat for it, I was one of many who stuck up for you. Dude, this is the kitchen and sometimes it gets warm in the kitchen. If you wanna mess in the kitchen, you gotta take the heat. You and everyone else in this thread are welcome to my campfire anytime. We all love this sport so why get hung up on some of our different ideas and approaches?

On the extreme example, sure, we can bend a thin jacketed bullet all out of shape if we pus it too hard... but c'mon man... that's not why the OP started this thread. Bullets fired within their operational parameters do not significantly change shape or mass from one rifle to another. It just doesn't happen, and if you think they do, prove it to me.

Til then, happy shooting and take care

 

[rscott5028]

MontanaRifleman,

I'm not trying to tell anyone how it is. I'm just trying to understand what you and others have learned through research. And, I respect your wisdom and experience which far exceeds mine.

As you acknowledged, the barrel engraves the exterior of the bullet. Not so much the head/ogive/meplat/boat tail which I assume has a larger influence on BC as compared to the bearing surface that gets etched. But, I think it has some affect which you and others say is very little. Perhaps even a tight barrel due to manufacturing tolerances or fouling may squeeze the OD enough to have an influence on BC?

So, while that little bit may be infintessimal at shorter ranges, I'm seeing credible sources saying that it's noteworthy at extreme ranges.

What I'm gathering from this thread is that BCs are imperfect to begin with. And, they are simply a mechanism to model the trajectory of a bullet giving us some predictability of where the bullet will intersect its target. Afterall, nobody practices at every 1 yard increment from 100-2000 yds.

As such, it seems reasonable to tweak the BC slightly for your rifle. But, any major fudging is likely due to either a misrepresented published BC or a wrong assumption on the part of the shooter.

In the case of the published BC, it's public forums like this which will likely bring that to light.

Whereas tweaking the BC substantially due to invalid assumptions about scope height/tracking, MV, etc.. is only going to set you up for disapointment under some set of conditions down the road.

Thanks,
Richard

 

[MontanaRifleman]

MontanaRifleman,

I'm not trying to tell anyone how it is. I'm just trying to understand what you and others have learned through research. And, I respect your wisdom and experience which far exceeds mine.

As you acknowledged, the barrel engraves the exterior of the bullet. Not so much the head/ogive/meplat/boat tail which I assume has a larger influence on BC as compared to the bearing surface that gets etched. But, I think it has some affect which you and others say is very little. Perhaps even a tight barrel due to manufacturing tolerances or fouling may squeeze the OD enough to have an influence on BC?

So, while that little bit may be infintessimal at shorter ranges, I'm seeing credible sources saying that it's noteworthy at extreme ranges.

What I'm gathering from this thread is that BCs are imperfect to begin with. And, they are simply a mechanism to model the trajectory of a bullet giving us some predictability of where the bullet will intersect its target. Afterall, nobody practices at every 1 yard increment from 100-2000 yds.

As such, it seems reasonable to tweak the BC slightly for your rifle. But, any major fudging is likely due to either a misrepresented published BC or a wrong assumption on the part of the shooter.

In the case of the published BC, it's public forums like this which will likely bring that to light.

Whereas tweaking the BC substantially due to invalid assumptions about scope height/tracking, MV, etc.. is only going to set you up for disapointment under some set of conditions down the road.

Thanks,
Richard

Richard, First off, I doubt that my knowledge and experience far exceeds yours and I appreciate your interest and contribution. I have a little experience and I paid attention in my high school and college physics classes and learned a little about laminar flow, etc., when I got my MS aerospace science.

There are a good number of credible posters in this thread, but by far, and I do mean by far, the most credible on this subject is Bryan Litz. Some folks have mention their experience in this threads and as I have pointed out a couple of times, Bryan's experience in this subject is very likely greater than all the rest of us put together.... not to mention his education in the science of it.... not to mention his superior facilities and equipment... not to mention his meticulous procedures. Next to Bryan, we are all novices at best.

If you were going to invest your life savings, would you go to a wet behind the ears kid fresh out of college or would you go to a long standing investment firm with a proven track record and experience in investment.

For some reason, some folks don't trust proven science which I just don't understand. Proven science IS reality, it's not voodoo or mojo. When you drop an object off a building, it begins and continues to accelerate until it hits the ground and we can, through testing and observation predict how long it will take to make the fall. Thanks to Isaac Newton, we know a lot about these physical realities and have been refining our knowledge over the years.

In reality, each different shape and density bullet will have it's own perfect drag coefficient or BC. That being said, we assign different profiles according to their likeness in shape... G7 for pointy, boattail, low drag bullets, etc... Bryan can speak more knowledgably about this, but basically the G7 model is good enough to make predictably accurate shot over the distance of ranges we shoot our low drag bullets... provided we input accurate data... and our equipment is set up properly, etc... garbage in, garbage out.

Back to experience and credibility. It is possible to fudge and get close enough to make our shots, and in reality that's what a lot of us do. But that doesn't mean the error is in the tested BC. If someone tells me they have been making LR shots for "x" no of years and they use a different than accurately tested BC, I will assume they are compensating for unknown errors until proven otherwise. I will put my $$$ with the proven investment firm.

Once again, Bryan can speak more knowledgably than I, but engraving just does not make that big a difference in the bullet's drag. When a bullet passes through the atmosphere, it disturbs air molecules which resist it's motion. The less these molecules are disturbed, the less drag the bullet will incur. We say that the molecules pass over the surface of the bullet, but in reality the bullet pushes them aside and slips between them, dragging along a few as it goes. The critical parts of this action are when the molecules pushed aside.... the meplat and nose... and the where they return to their original position, the tail. The more orderly this occurs, the less the resistance to the bullets progress. Engraving has very little effect on this and neither do driving bands or transverse cut grooves that are found on many monometals. I suspect this due to a very thin low pressure area surrounding the shank of the bullet created by the outward push of air molecules from the nose- just a guess.

In short, I do not see how a typical rifle bore will change the drag properties of a bullet more than another typical rifle bore. Having said that, there may be other physical realities in play here, such as spin drift, pitch and yaw, etc... but they in reality do not affect the BC of the bullet, just it's path.

Cheers,

Mark

 

[Michael Eichele]

, there may be other physical realities in play here, such as spin drift, pitch and yaw, etc... but they in reality do not affect the BC of the bullet, just it's path.

Cheers,

Mark

Sierra dissagrees. They have proven that coning can affect a BC by as much as about 10% if my memory serves me right. Bullets can cone even when stabilized properly. They have also proven that even though a bullet can be 'stable', when they are on the lower limit of the stability factor they can be 30% lower compared to those that are higher. Granted, when they are in the mid and upper end of the GS factor, there is little difference in BC between different GS factors like say 1.3-2.0.

Sierra also did not use the bullet's paths to determine these figures. They uses near velocity, far velocity AND time of flight.

Is Sierra Bullets 'credible'?

 

[MontanaRifleman]

If you don't want your bullets deformed don't put them in your chamber. Its that simple. All barrels reshape the bullet to one degree or another. If you wish you can take a rifle a single raw bullet and a hammer and see if you can get a bullet to go down your barrel without using the hammer.

Who said I don't want my bullets deformed?

BB, bullets just dont get deformed to any SIGNIFICANT difference by a rifle bore. I just measured the body of an E-Tip I revored @ 500 yards that pentrated a plywood target and plowed into frosted dirt, sand and gritty rock fragments behind it. It measured .307, identical to a new one fresh out of the box. It's tail is exactly the same, but it's nose is a little different eh. I think we know why that is and if anypart of the bullet would affected by the bore it would be the shank. So I think it's safe to assume that the nose left the bore in the same condition it entered it. Yeah, it's a monometal, but it is not tough enough to flex the bore outward to maintain it diameter any more than a jacket bullet. Maybe you think that the nose/ogive area of the jacketd bullet is slumping under pressure? If it is, I will suggest that you will get terrible accuracy with such a conditon.

As for the other experiences that members have posted, as I said previously, I will assume they have unknown erros in their results until proven otherwise. and I think I have sound reason to do so.
Some reading for you on this threadr

Somewhere in this forum is a discussion by Kirby of the many different barrels he tried during the early stages of developing the 7AM and adapting it to the 200 grain wildcat bullet. What he found was when you had more that 25% IIRC of the bearing surface under compression you began affecting the bullet adversely.

I don't doub it. But when you start adversley affecting the bullet, it's time to try something else. I do not believe we are discussing that. That's throwing oranges into a bushel of apples.

My advice to you is to go ahead and build your 56.5-375 Ruger and shoot soft bullets in it such as the 140 Berger out to a mile and keep careful records of your drops for about 500 rounds. And every once in a while let it go 50 rounds without cleaning. Also every once in a while take a shot at an animal at a mile where it really matters if you land the first (and only) bullet correctly. You will learn many strange and interesting things.

I may take you up on that advice, but I have a feeling that the B 140's will not hold up in that rifle.

I also have some advice for you, the next 257 or 7AM barrel you get, try nitriding them and feel free to shoot them without worry of quick errosion gun)

 

[MontanaRifleman]

Sierra dissagrees. They have proven that coning can affect a BC by as much as about 10% if my memory serves me right. Bullets can cone even when stabilized properly. They have also proven that even though a bullet can be 'stable', when they are on the lower limit of the stability factor they can be 30% lower compared to those that are higher. Granted, when they are in the mid and upper end of the GS factor, there is little difference in BC between different GS factors like say 1.3-2.0.

Sierra also did not use the bullet's paths to determine these figures. They uses near velocity, far velocity AND time of flight.

Is Sierra Bullets 'credible'?

Hey Michael, I thought you were in waiting for your rig to get back from the smith I guess it's my turn to be put through the washing machine

Intersting stuff... I don't know much about "coning" but would like to learn. If you any article refferences, I would like to read them before drawing any conclusions. and yeah, i think Sierra is credible... but I would like to actually see their data and conclusions.

Next time you're in Momtana, give me a buzz and we'll test BC theories on some PD's

 

[rscott5028]

Having said that, there may be other physical realities in play here, such as spin drift, pitch and yaw, etc... but they in reality do not affect the BC of the bullet, just it's path.

Mark,

We're into semantics now and my feabile attempt to apply common sense is perhaps dangerous.

While they may not affect the real BC of the bullet, the actual flight path dictates an effective BC in my way of thinking.

My perspective is that if anything affects the path in a consistent and repeatable manner, then I should change something in the calculation to account for that in order to predictably estimate the POI at a given distance.

Fudging MV, scope height, atmospheric conditions seems unreasonable assuming I can even measure those accurately. So, a slightly different BC might be in order.

As such, I'm not in disagreement with Bryan about his research. Rather, his results are simply a statistical estimate of the BC of each future bullet produced and fired based on a set of variables, controls, and experiments for which he has an excellent reputation of making accurate representations.

I'm going to respectfully bow out here and start reading Bryan's work. I'll no doubt learn more there than from speculating.

Thanks!
Richard