|
|
Joined: Mar 2007
Posts: 20,203
Campfire Ranger
|
Campfire Ranger
Joined: Mar 2007
Posts: 20,203 |
longer is more stable and more wind resistant, all other things being equal I get that speed is the biggie in determining wind drift, for the most part. That makes perfect sense, but in theory wouldn't a longer bullet (assuming the same b/c and diameter) have more surface area for wind to act upon and thus drift more? The other variable to consider is that the longer the bullet, the more twist it takes to stabilize it. More twist keeps it more steady on it's axis and helps counter act effects of wind. As an example, think of a football that is spun and thrown in a spiral vs a non spiral lame ass throw. The one thrown in a spiral deflects less off target in the wind. Sure, but (I suspect) it is due to a spinning and stabilized football keeping its speed longer and then in turn bucking wind better: this is not necessarily because of the spinning itself, right? Maybe I am misreading your post but the rifle's twist itself shouldn't have a bearing on a bullet's B/C. Right? Hell if I know.
|
|
|
|
|
Joined: Mar 2007
Posts: 20,203
Campfire Ranger
|
|
Campfire Ranger
Joined: Mar 2007
Posts: 20,203 |
So, a baseball and a same sized nerf ball have the same B/C? It sure seems like a baseball thrown at the same velocity has a much higher B/C, as it keeps its speed much longer and generally goes further. Drag coefficient I can see based solely on bullet profile, but not the actual ballistic coefficient. Apparently velocity also plays a factor and B/C can change with velocity, which gets me doubly confused.
I am totally lost here...
In the most simple of terms think a rocket design in a wind tunnel. You’re not trying to establish how much fuel it will take to get the rocket to where it’s going, or how fast it has to be at launch, you’re strictly trying to establish which one is less affected by wind/resistance. The other problems are addressed elsewhere. BC just establishes how slippery the projectile is. That makes sense, for the drag coefficient at least. I still am not seeing how mass doesn't have an affect on the actual B/C, as mass gives momentum. That is of course assuming the posters saying that mass or weight has no bearing on B/C are correct (which is a big assumption). Most every link I see on Google Fu says mass is a function of B/C. If you wanna be a scientist, go be a scientist. For the purposes of an end user BC means how slippery the bullet is and nothing else. It should also be noted that bullet makers lie for the sake of selling schit and proof is always in the pudding. I don't want to be a scientist. I just want to drink cheap beer and shoot things. As far as inflated B/Cs, the long range accubonds are the posterchild, and just one of many reasons I rarely play with noslers anymore.
|
|
|
|
|
Joined: May 2004
Posts: 56,097
Campfire Kahuna
|
|
Campfire Kahuna
Joined: May 2004
Posts: 56,097 |
But it does have an effect, sorry.
Low stability = wobbles and increased drag
High stability may cause the bullet to hold a slight nose up attitude and what is called 'yaw of repose' as it drops, plus a drift one way or the other depending on twist. Can this be managed? Yep. Being aware is the first step to success.
One effect of excessive stability at long range is that it is likely to cause the bullet to tumble when it transitions the speed of sound.
I am..........disturbed.
Concerning the difference between man and the jackass: some observers hold that there isn't any. But this wrongs the jackass. -Twain
|
|
|
|
|
Joined: Mar 2007
Posts: 20,203
Campfire Ranger
|
|
Campfire Ranger
Joined: Mar 2007
Posts: 20,203 |
That makes sense, for the drag coefficient at least. I still am not seeing how mass doesn't have an affect on the actual B/C, as mass gives momentum. That is of course assuming the posters saying that mass or weight has no bearing on B/C are correct (which is a big assumption). Most every link I see on Google Fu says mass is a function of B/C. Mass, velocity,, point of aim, and BC are all major actors in determining trajectory. But BC is separate from mass and velocity. You can think about it this way: Momentum is the "fuel" that makes a projectile go. As drag acts on the projectile, the projectile sheds momentum. The hollow aluminum shell and the solid tungsten bullet with the same shape will have the same drag. But the aluminum shell does not have much momentum, so it "gives up" in a hurry. Wind deflection does not mostly come from the wind blowing against the side of the bullet. It happens because the bullet will very slightly "nose into" a crosswind, because that is the orientation of least resistance. So you have the drag vector pointing out of the base of the bullet, and it mostly points toward the muzzle, but slightly points toward the side. It's that component pointing toward the side that moves the bullet sideways. So bullets with higher BC are less deflected by the wind. This makes good sense. Thanks for that. I still think folks are confusing drag coefficient with ballistic coefficient though, as every source google finds for me to determine B/C has a mass component. Maybe I will eMail Mr. Litz and ask. We're bros.
|
|
|
|
|
Joined: Jun 2004
Posts: 44,820
Campfire 'Bwana
|
|
Campfire 'Bwana
Joined: Jun 2004
Posts: 44,820 |
BC does have a mass component. But once it's figured then it's figured. So a 95 gr. 6mm having the same BC as a heavier 30 cal will share flight characteristics.
|
|
|
|
|
Joined: Sep 2004
Posts: 8,151
Campfire Outfitter
|
|
Campfire Outfitter
Joined: Sep 2004
Posts: 8,151 |
[It should also be noted that bullet makers lie for the sake of selling schit and proof is always in the pudding.
Going full-on Cosby on us now? . . . Brian Litz administers the truth serum . . .
|
|
|
|
|
Joined: Mar 2007
Posts: 20,203
Campfire Ranger
|
|
Campfire Ranger
Joined: Mar 2007
Posts: 20,203 |
But it does have an effect, sorry.
Low stability = wobbles and increased drag
High stability may cause the bullet to hold a slight nose up attitude and what is called 'yaw of repose' as it drops, plus a drift one way or the other depending on twist. Can this be managed? Yep. Being aware is the first step to success.
One effect of excessive stability at long range is that it is likely to cause the bullet to tumble when it transitions the speed of sound. Ok, this is the kind of info I am looking for. Thanks for that. Obviously a wobbling and tumbling bullet will signifigantly increase drag and slow down. I wasn't referring to a bullet that wasn't stabilized at all, just one that isn't spinning really fast as opposed to one spinning fast enough to stabilize. Good thread! I am picking a few things up.
|
|
|
|
|
Joined: Mar 2007
Posts: 20,203
Campfire Ranger
|
|
Campfire Ranger
Joined: Mar 2007
Posts: 20,203 |
BC does have a mass component. But once it's figured then it's figured. So a 95 gr. 6mm having the same BC as a heavier 30 cal will share flight characteristics. That makes perfect sense. Thanks.
|
|
|
|
|
Joined: May 2004
Posts: 56,097
Campfire Kahuna
|
|
Campfire Kahuna
Joined: May 2004
Posts: 56,097 |
Teach your kids. When they get into an egg fight there’s a difference in BC between chicken and sparrow eggs.
I am..........disturbed.
Concerning the difference between man and the jackass: some observers hold that there isn't any. But this wrongs the jackass. -Twain
|
|
|
|
|
Joined: Jan 2016
Posts: 11,979
Campfire Outfitter
|
|
Campfire Outfitter
Joined: Jan 2016
Posts: 11,979 |
|
|
|
|
|
Joined: Jan 2007
Posts: 416
Campfire Member
|
|
Campfire Member
Joined: Jan 2007
Posts: 416 |
One effect of excessive stability at long range is that it is likely to cause the bullet to tumble when it transitions the speed of sound.
Interested to hear more as that has not been my experience in testing twists as fast as 1:4 in .308. My experience has been just the opposite. I have measured improvements in both BC avg and BC SD in faster twist barrels for some (not all) bullets. Lots of good info in this thread and some bad. Looks like the good is winning out. Bryan Litz has a great chapter on BC in one of his books. It is a really good read. He is a really good guy. I can't recommend his work more strongly. Actually measuring BC used to require expensive equipment. No more. The Oehler '89 costs less than a lot of scopes that enthusiasts use.
|
|
|
|
|
Joined: Dec 2004
Posts: 14,488
Campfire Outfitter
|
|
Campfire Outfitter
Joined: Dec 2004
Posts: 14,488 |
Interested to hear more as that has not been my experience in testing twists as fast as 1:4 in .308.
BufordBoone, what bullets did you play with, and what was the longest range you played with in that beast? Were you able to discern any effects of reduction or loss of tractability?
Don't be the darkness.
America will perish while those who should be standing guard are satisfying their lusts.
|
|
|
|
|
Joined: Apr 2006
Posts: 9,518
Campfire Outfitter
|
|
Campfire Outfitter
Joined: Apr 2006
Posts: 9,518 |
Teach your kids. When they get into an egg fight there’s a difference in BC between chicken and sparrow eggs. Where do Emu mortars factor into the egg-fight?
I can walk on water.......................but I do stagger a bit on alcohol.
|
|
|
|
|
Joined: May 2004
Posts: 56,097
Campfire Kahuna
|
|
Campfire Kahuna
Joined: May 2004
Posts: 56,097 |
OK, Now I'm Serious.  I do mean stuff when I'm serious. You'll need two cups of java to muck your way thru this. http://www.nennstiel-ruprecht.de/bullfly/
I am..........disturbed.
Concerning the difference between man and the jackass: some observers hold that there isn't any. But this wrongs the jackass. -Twain
|
|
|
|
|
Joined: Jan 2007
Posts: 416
Campfire Member
|
|
Campfire Member
Joined: Jan 2007
Posts: 416 |
Interested to hear more as that has not been my experience in testing twists as fast as 1:4 in .308.
BufordBoone, what bullets did you play with, and what was the longest range you played with in that beast? Were you able to discern any effects of reduction or loss of tractability? Various bullets. One that showed most improvement was the 168 Matchking. I don't recall the distance to which radar measurements tracked the bullets. Probably on the order of 1.5K. I don't own a radar system capable of tracking bullets beyond about 100 yards. However, in some "Thru the Sonic" testing I did with an Oehler '88, I downloaded and shot the bullets in a 1:7 and then a 1:4 and compared. I started them at about 1700 and measured BC at about 250 and 800 (the '88 has the capability to measure at up to three downrange locations). What do you mean by "reduction or loss of tractability"?
|
|
|
|
|
Joined: Dec 2004
Posts: 14,488
Campfire Outfitter
|
|
Campfire Outfitter
Joined: Dec 2004
Posts: 14,488 |
What do you mean by "reduction or loss of tractability"?
That would be when the axis of the bullet's spin does not remain tangent to the trajectory. In other words, the bullet would more or less belly-flop into the target (if it was hit at all). ![[Linked Image from i.imgur.com]](https://i.imgur.com/VaZt1Tc.gif) I would imagine it would require a shot of around 2500 to 3000 yards to see evidence of it happening, but that's just a guess. I am not aware of anyone ever having demonstrated the phenomenon with a rifle. My understanding is that it was observed in the early days of firing artillery at higher angles of elevation.
Don't be the darkness.
America will perish while those who should be standing guard are satisfying their lusts.
|
|
|
|
|
Joined: Jan 2007
Posts: 416
Campfire Member
|
|
Campfire Member
Joined: Jan 2007
Posts: 416 |
What do you mean by "reduction or loss of tractability"?
That would be when the axis of the bullet's spin does not remain tangent to the trajectory. In other words, the bullet would more or less belly-flop into the target (if it was hit at all). Interesting. Had not heard that term used that way before. I've not tested for it but would be a fun/interesting thing to do. Thanks for the information.
|
|
|
|
|
Joined: Dec 2019
Posts: 17,067
Campfire Ranger
|
|
Campfire Ranger
Joined: Dec 2019
Posts: 17,067 |
so is cross sectional area the same as frontal area? meaning A is constant for a given caliber.
-OMotS
"If memory serves fails me..."
Quote: ( unnamed) "been prtty deep in the cooler todaay "
Television and radio are most effective when people question little and think even less.
|
|
|
|
|
Joined: May 2004
Posts: 56,097
Campfire Kahuna
|
|
Campfire Kahuna
Joined: May 2004
Posts: 56,097 |
Good question. I’m inclined to say no, but it would depend on the definition of frontal area. It is a metric I’ve not seen referenced in calculation.
Cross section area would be R^2 x Pi. My spin on ‘frontal area’ would be the surface area of the bullet nose, tip to caliber diameter of the bullet.
A would be a caliber constant.
I am..........disturbed.
Concerning the difference between man and the jackass: some observers hold that there isn't any. But this wrongs the jackass. -Twain
|
|
|
|
|
Joined: Jun 2004
Posts: 11,115
Campfire Outfitter
|
|
Campfire Outfitter
Joined: Jun 2004
Posts: 11,115 |
All this had me questioning some of the things I thought I knew. So, back to the books....
Harold Vaughn was a serious shooter, and his day job was working out ICBM trajectories in air, so they would hit their target. He wrote the book Rifle Accuracy Facts, which is not too well known, but a real treasure.
I was sure that BC was only a function of shape. I was incorrect.
Somehow I missed DigitalDan's post, but found the same information in Harold's book, put in different units of measure:
BC = .0000714 * W/(D^2 * Cd) * σ
Where
W is weight in grains
D is caliber in inches
Cd is the drag coefficient
σ is an air density factor
So calculating BC DOES involve weight or mass.
I can see that I never accorded DigitalDan as much respect as he deserves.
Be not weary in well doing.
|
|
|
|
|
266 members (450yukon, 1_deuce, 338reddog, 10gaugemag, 2500HD, 300_savage, 41 invisible),
2,430
guests, and
1,198
robots. |
|
Key:
Admin,
Global Mod,
Mod
|
|
|
Forums81
Topics1,191,386
Posts18,469,694
Members73,931
| |
Most Online11,491
Jul 7th, 2023
|
|
|
|
