[Goose]

Originally Posted by CD

The bullet then flies in an arc shaped trajectory and if the settings are correct, you will hit the bulls eye at each distance. Bullet weight, amount of the charge, air density and wind conditions are the main variables.

Bullet weight has nothing to do with velocity loss/drop at range. What matters is the ballistic coefficient of the bullet and the initial (muzzle) velocity. These are the only two variables in an exterior ballistics equation.

[CD]

Huh?

For a given charge, in the same wind and weather conditions, wouldn't a 200 grain 30.06 round drop faster than a 150 grain round? Time in flight would be the same correct? But, because the initial velocity is higher, the mass is lower, drag and gravity takes longer to affect the 150 gr round right?

In other words, if you secure a 30.06 rifle so that the barrel is 32" from the ground with 0º elevation and you fire a 150 grain and 200 grain bullet with the same charge, which one goes further down range before impacting the earth? While flight time remains the same, why would the 150 grain bullet fly further than the 200 grain round given that they are the same profile?

Or, are you saying that the initial velocity of the 150 gr round is higher than the 200 gr round, flight distance is further for the 150 gr bullet?

I was thinking more along the lines of best glide distance at best glide speed for an aircraft like a Cessna 172 at max and min gross weights. But, then the AOA required to maintain 65 KIAS is different so...might have answered my own conundrum....

[Goose]

CD, true only to the extent that a given design bullet in a given caliber will usually have a higher BC than a lighter one. However, consider the 220 grain round nose .308 diameter bullet vs the 150 grain boat tail which has a higher BC because it's more aerodynamic. In the equations, and I've written exterior ballistics programs and have the equations stashed somewhere around here, all you enter as variables is BC and muzzle velocity. That's all that matters. The weight of the bullet is irrelevant to the equations. After all, in a vacuum, a feather falls just as fast as a bowling ball. Now, we don't live in a vacuum, so aerodynamics comes to play, but for the drop of a bullet at a given velocity for a given BC with two different bullet weights, say a 200 grain .308 flat base that has the same BC as a 140 grain boat tail, equal velocity at the muzzle remember, time in flight will be the same and drop from muzzle centerline with be the same because both are slowing down at the same rate. Speed up the lighter bullet and you have a flatter shooting gun.

A good ballistics program is available on the net, just google PCB1.8. Also, you can get a good chronograph for well under $100. I gave about $60 for mine about 25 years ago when the Shooting Chrony first came out and the base model hasn't gone up much, very useful tool for working up handloads. I really want an Ohler with the strain gauge for measuring chamber pressure, but can't justify the cost as little load development as I do anymore. I'd thought about gettin' into the bullet swagging business for a while, but gave up the idea. It'd be fun, but I doubt it'd be very profitable.

Thought I'd add, Newton's gravitational acceleration law is D+1/2g (t^2) where D is distance fallen, g is the gravitational acceleration constant 32 ft/second squared, and t is time. There is no variable for mass in Newton's equation. A feather released from the top of a 100 story building will indeed be falling as fast as a Volvo released there when they hit (velocity is the first derivative of the equation). Release that feather and that Volvo at the same time from the same building and they both hit the ground at the same time.....if there is no air. This only would work on the moon.

[Tomflhrci98]

Hey Goose,

Newton went further and discovered that the Volvo made a bigger dent in the ground then the feather and this is where the mass comes into play (even on the moon).

A heavier bullet will punch thru the air better then a lighter bullet of same size and shape.

I don’t mean to argue with you, but, it seams to me that your “BC” number is not just air friction, but a combination of air friction (due to size and shape) and mass. No?

I think Newton would have driven a Volvo, he seams like a yuppy.

[2fastnaz]

Man that's a trip. Hope your friend is doing well. I'd sure like to know what caliber that is. Maybe .220 swift or .221 fireball, looks to big to be a .17 to me.

[Goose]

Mathematically, the ballistic coefficient is the ratio of a bullet's sectional density to its coefficient of form. Sectional density is a function of the bullet's weight. To calculate a bullet's sectional density divide the bullet's weight (in pounds) by its diameter (in inches), squared. The higher the SD number the better the SD, and the heavier a bullet is in proportion to its diameter.

So, yes, BC is related to weight as it is related to sectional density. However, a list of BCs for common bullets will readily show you that aerodynamic drag, a function of the coefficient of form, is more important than the weight of the bullet in exterior ballistics. And, in reality, weight is only important in the SD calculation as it describes the length of the bullet as to its diameter. That affects aerodynamic drag. Here are some common BCs for different bullets. Notice the .25 caliber bullets (max 117 grains) with higher BCs than .375 caliber bullets of 270 grains weight.

224" (.22) 55 grain, BC .255
.243" (6mm) 90 grain, BC .385
.243" (6mm) 100 grain BT, BC .430
.257" (.25) 100 grain BT, BC .393
.257" (.25) 120 grain BT, BC .435
.264" (6.5mm) 120 grain, BC .433
.264" (6.5mm) 140 grain, BC .496
.277" (.270) 130 grain BT, BC .449
.284" (7mm) 145 grain, BC .457
.308" (.30) 150 grain BT, BC .423
.308" (.30) 165 grain BT, BC .477
.311" (.303) 150 grain, BC .411
.323" (8mm) 150 grain, BC .369
.338" (.338) 200 grain, BC .448
.375" (.375) 270 grain BT, BC .429

Bullets with high sectional density are long for their diameter (the weight has to come from length if the diameter is fixed). Therefore, these bullets will tend to have higher BCs for a given ogive and bullet type. Bullets of 6.5mm and 7mm tend to be some of the highest BCs in sporting rifle calibers, in fact, because of their weight compared to their diameter, IOW, they also have a high sectional density. Short, fat, heavy bullets are not what you want for a high BC. Bullets like the 400 grain .45-70 flat nose can be pushed to near 2100 fps out of a stout rifle like the Ruger number one. However, my lowly .30-30 Contender pistol with 12" barrel shoots a 150 grain Nosler ballistic tip to 2100 fps and is much flatter shooting than the rainbow trajectory .45-70. The reason is the Nosler's BC is .435, the .45-70 400 grain pill is .272, significantly lower than the .30-30 150 grain pill and the big .45 looses velocity faster because its wind resistance is higher. Weight has no effect.

The only variables involved in calculating bullet drop from center line of bore (trajectory) are BC and initial velocity. Now, in that BC is a function of sectional density and sectional density is a factor of weight and diameter, weight is a factor in calculating the BC. However, it's not a big factor and it's only a factor in describing the length of the bullet to its diameter and has no effect on the actually bullet trajectory on its own.

That Volvo and that feather fall at the same rate in a vacuum. They arrive at the ground at the same time. I didn't make reference to energy or momentum which of course favor the Volvo because they are a function of mass and velocity. Velocity loss of the bullet at distance, therefore time of flight of the bullet, therefore drop from centerline of the bullet are determined by other factors, not energy or momentum. Energy and momentum are important as to what happens in TERMINAL ballistics, what happens when bullet hits bone, but not in exterior ballistics, what happens between the muzzle and the skin of the target.

[Goose]

Originally Posted by 2fastnaz

Man that's a trip. Hope your friend is doing well. I'd sure like to know what caliber that is. Maybe .220 swift or .221 fireball, looks to big to be a .17 to me.

It is a FMJ .223" bullet no doubt from a .223 (aka 5.56mm Nato). John has it. I don't know if he's going to make a necklace out of it, but I would.

[Tomflhrci98]

NEVER QUESTION GOOSE ABOUT BALLISTICS

Thanks Goose. That is a great answer. I had to read it a couple of times to get the full affect. So it makes sense then that the lower coefficient of form counteracts the sectional density which makes it more important than the weight factor.

Excellent info. I didn’t mean to make you work hard. I was just trying to carry a thought process through. You know you’re stuff. Do you own a gun store?

I can’t get over all the unrelated stuff I learn on this motorcycle forum

[Goose]

Well, I've been into handloading and guns and such for a while and read a lot about it over the years and live down the street from a Holiday Inn. Guns and motorcycles and the things you do with them (tour, race, hunt, competition) have been my thing for about most of my life. Funny, but reading various motorcycle and gun boards, I'm not alone. They do seem to go together as past times for some reason.

To correct a bit, the weight of the bullet in the BC calculation is only relevant as to the fact that it is a measure of the bullets length to it's diameter (sectional density). IOW it helps determine how aerodynamic the bullet is as well as it's form (ogive/shape). But, anyway, you got the point pretty well. It's a fairly complicated subject and unless you're a complete nut about your hobby like I've been, it probably don't make a hill of beans to ya. ROFLMAO! But, when I take on a hobby, I go a little stupid crazy about the details sometimes.

[voodoo1]

All I know is that had to cause a bit of panic... how long did it take to figure out what it was? could he tell right away?
Wish him a speedy recovery.

[Goose]

It never broke any bones, so they just pulled it out and put bandaids on it. He said he didn't actually feel it at first, heard the crack of the bullet. Everyone says "WTF was that?" and Jon Whitfill looks at his foot and says, "Dude, you've been shot!". Funny now, but wasn't at the time.

[bikerjim1]

Jeez, what er' the chances! Good thing is, it coulda been his head er' something!