.308 Bullet Drop Rules of Thumb

S

Steve McCullagh

New member
I was staring at some ballistics charts the other day, in order to commit the basics to memory. One particular set of
numbers for bullet drop struck me with a pattern:

150 gr ball .308, zeroed at 100yds can be reckoned by powers of 2

150 yds ~= 1" = 2^0
200 yds ~= 4" = 2^2
250 yds ~= 8" = 2^3
300 yds ~= 16"= 2^4

150 gr ball .308, zeroed at 200 yds can be reckoned thus:

250 yds ~= 4" = 2^2
300 yds ~= 8" = 2^3
400 yds ~= 32"= 2^5
500 yds ~= 64"= 2^6

Naturally, behavior will vary with the numerous variables, so this isn't good for a precision shot. (All of these
"guesstimates" are within 1/4 MOA for the true path of the
load given.) It is good, however, if everything goes to
hell in a handbasket and you have to guess, or you're
trying to give a novice some rough 'n ready numbers...
Anyone have some dope on .308 zeroed at 300 or 400 yds?
Has anyone come up with other similar handy patterns
for other calibers?

-Steve
 
Hey I like this Post I just had a post up a few days ago about 150gr bullet drop at 500yds. Can you explain to this Amatuer what those numbers you posted mean and what those squiggly lines are? I'm all ready to print that out if a few people give me a thumbs up?
 
The squiggly lines mean "approximately equal to".
Laxman gave a good explanation of what the exponentials were. My memory is suffering from overcrowding, and
frequently makes random evictions, so the easier something
is to remember, the more likely I'll have it around when
I need it. :)
 
Dropsy/Thumbsy

Generalizin' in my usual happy fashion: For a whole bunch of cartridges calibers above the hot center-fire .22s and not including magnums, the trajectories are roughly the same. Well, "same enough" for general hunting purposes, out to around 300 yards.

Say, the .243 with 100-grain bullets; the .257 Roberts class; .270 and .308 and '06, etc.

If you sight in for two inches high at 100 yards, you're gonna be zeroed at 200, and roughly six inches low at 300. That means that if you don't need binoculars to tell that it's a coyote and not your neighbor's dog, point it and pull. If the deer looks just real good to your nekkid eyeball, don't hold over; just point it and pull.

And if you're really concerned about longer distances, they're all gonna be right at two feet low at 400 yards and four feet low at 500 yards.

And your eyeball can't tell the difference between 400 and 500 yards, anyway.

:), Art
 
You are halfway thru High School Physics.

As soon as you know what the Gravitational Constant (G) is, report back to us with the complete formula. :D
 
Art is right!!!

For the "normal" big game calibers like the above mentioned, guesstimation is only OK up to 300 yards max. (and knowing where is your limit is the name of the game). If you plan to shoot beyond those 250-300 yards, then you'll need a lot of experience with wind deflection estimation, some means to estimate range very accurately, and a scope with some dots, lines, etc. in the reticle or target knobs to "click-up", in addition to knowing exactly your bullet path.
 
Actually, I'm all the way through university physics. :p The point of having rules of thumb is to avoid arduous calculations, or lots to remember.

(The gravitational constant (6.67E-11 m^2/kg^2) is only of value in recalculating the rate of acceleration due to Earth's gravitational pull. This is more handily remembered
as 9.8 m/s^2 - a useful number for ballistic calculations. It does presume upon being at the mean distance from the Earth's center, but it is sufficiently accurate for our purposes.)

Art & Ruben are certainly right in stating that it's not terribly reliable to "eyeball" ranges greater than 300 yds or so. With some practice, you can become pretty adept at estimating range with just a Duplex reticle. Gauging wind deflection is definitely an art form, as variable wind conditions along the bullet's path can make calculations a real chore! There is a good article on this in the August (?) _Tactical Shooter_...
 
SuperDave, It's funny you mentioned that. Missles take the movement of the earth into account during their navigation! Obviously, bullets aren't traveling as far!
 
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