Scope and bullet drop math

[RedneckFur]

I've been trying to work this out in my head, but I havent had much luck. Most of my shooting has been confined to shooting at 100 yards with scopes with 1/4" clicks.

For about a year now, I've had a remington 700SPS in .308 winchester Mounted on the rifle I have a Bushnell Elite 4200 8-32x40, with 1/8" clicks for adjustments.

I have the rifle zeroed for 100 yards, and it easily cloverleafs with 168gr. sierra 168gr matchkings. powder I use is 41.5 gr. of reloader 15.

My rifle range has target frames out to 300 yards. I want to shoot my rifle out at this range, but I'm unsure of how to get there. at 100 yards, my rifle scope only has 20 inches of possible travel.

Roughly speaking, how much bullet drop would I see at 300 yards? Would I have enough adjustment to even get the crosshairs on target at this range?

I'm aware that as distances increase, so does the amount of ajustment in each scope click. if one click is 1/8" at 100 yards, would I be safe to assume 1/4" at 200 yards? Would I have 1/2" at 300 yards?

I have a windage adjustable scope base and rings, but I feel that i'm limited in the amount of vertical adjustment I have. Can I shoot this combination to 300 yards and possibly beyond? Should I sell the scope and look for something with more adjustment?

Thanks for you help!

 

[Coltdriver]

The thing that you can not tell is the fps of your round. If you can borrow a chronometer then there is another way.

This will get you real close to knowing your actual fps.

If you are spot on at 100 yards then adjust poi up so that you are 2 inches high when you aim at the bullseye.

Then shoot a 200 yard target and see where you hit.

Then look up a ballistics calculator on the web and plug in your numbers until you get the arc it describes to match what you are shooting. You will have to try several fps entries to get the calculator to describe your arc. When you do you can calculate how low it will hit at 300 yards. That arc will also have the fps you are at or very close to it.

20 inches of adjustment is plenty as long as you are not shooting the round at such a low velocity that it has a lot of arc out to 300 yards.

 

[zoomie]

For about a year now, I've had a remington 700SPS in .308 winchester Mounted on the rifle I have a Bushnell Elite 4200 8-32x40, with 1/8" clicks for adjustments.

I have the rifle zeroed for 100 yards, and it easily cloverleafs with 168gr. sierra 168gr matchkings. powder I use is 41.5 gr. of reloader 15.

My rifle range has target frames out to 300 yards. I want to shoot my rifle out at this range, but I'm unsure of how to get there. at 100 yards, my rifle scope only has 20 inches of possible travel.

Roughly speaking, how much bullet drop would I see at 300 yards?

First thing is to quit thinking in "inches." Instead, think in Minutes of Angle (MOA). Play around with this: http://www.jbmballistics.com/calculations/calculations.html.

Using a MV of 2500 and your 168 SMK, you'll only need about 5 MOA of elevation correction. So your scope is plenty capable (mechanically) of reaching your 300 yard zero.

Would I have enough adjustment to even get the crosshairs on target at this range?

Yep.

I'm aware that as distances increase, so does the amount of ajustment in each scope click. if one click is 1/8" at 100 yards, would I be safe to assume 1/4" at 200 yards? Would I have 1/2" at 300 yards?

3/8" @ 300 yards. But again, don't think in inches. Think in MOA. "I need 5 MOA of adjustment for 300 yards."

I have a windage adjustable scope base and rings, but I feel that i'm limited in the amount of vertical adjustment I have. Can I shoot this combination to 300 yards and possibly beyond? Should I sell the scope and look for something with more adjustment?

You've got plenty of adjustment, especially for moderate distances. I show you'd run out of elevation (assuming you have 20 MOA adjustment left from your 100 yard zero) at between 600 and 700 yards. After that you'd need a bigger scope or slanted scope base.

Go read here, too.

http://demigodllc.com/articles/practical-long-range-rifle-shooting-equipment/
http://demigodllc.com/articles/practical-long-range-rifle-shooting-optics/
http://demigodllc.com/articles/practical-long-range-rifle-shooting-shooting/

 

[wyobohunter]

This is for a scope with 1/4 MOA adjustments

100 4 100 0.25
150 3 150 0.375
200 2 200 0.5
250 1.625 250 0.625
300 1.25 300 0.75
350 1.125 350 0.875
400 1 400 1
450 0.875 450 1.125
500 0.75 500 1.25

The first two colums are yards and clicks per inch while the second two are yards and inches per click.

For a scope with 1/8 MOA adjustments just double the Clicks per inch and 1/2 the inches per clicks. Somebody should double check this to confirm as I just made a spreadsheet at home to bring to the range with me & I'd like to know that it's correct.

 

[jmr40]

Your makin this way harder than it has to be. If your 308 is zeroed at 100 yards it should be on the paper at 300. Put up a target at 300 and start shooting. Make adjustments as necessary.

 

[wyobohunter]

Your makin this way harder than it has to be. If your 308 is zeroed at 100 yards it should be on the paper at 300. Put up a target at 300 and start shooting. Make adjustments as necessary.

This is true, but it would help to sight in about 2" high at 100 yards first.

My 30-06 is sighted 2" high at 100 yards and hits 8" low at 300 yards. This is at 2700 fps using a 180 gr. Swift Scir. II poly tipped boat tail (B.C. is .52).

 

[Brian Pfleuger]

I'm aware that as distances increase, so does the amount of ajustment in each scope click. if one click is 1/8" at 100 yards, would I be safe to assume 1/4" at 200 yards? Would I have 1/2" at 300 yards?

Almost, but not quite. The adjustment changes by the amount of the "click" for every multiple of distance. 200 yards is times 2, so 1/4, 300 yards is times 3, 3/8. 400 would be times 4, 1/2..... and so on.

 

[sneaky pete]

"The rule of COMEUPPINS"

old Sneaky Pete here: I'm an old "Brown Shoe" Marine and carried an M1 Garand with a 1 MOA rear sight elevation adjustment and The Rule of COMEUPPINS( that means how many clicks{1-MOA}you come up) with a zero at 100 yds is
from 100>200--2 clicks, fm 200>300--2 clicks, fm300>400--3 clicks, fm 400>500--3 clicks, fm 500>600--4 clicks, fm 600>700--4 clicks, fm 700>800--5 clicks, fm 800>900--5 clicks, fm 900>1000--6 clicks. Now this is wth a 150gr m-2 ball FMJ( my m-2 ball chronos @2750 FPS+/-) --but you get the general idea--and with your 1/8 MOA scope adjustment obvously multiply X8 so then you should come up 32 clicks with your scope---at least that should get you in the 10 ring. THANX--SNEAKY

 

[Flatbush Harry]

Long-Range Trajectory (.308Win)
Cartridge Type Bullet 100 150 200 250 300 400 500
Remington® Express® 168 BTHP Match 2.1 1.8 zero -3.4 -8.6 -24.7 -49.9


This is from Remington's ballistics page for their 168gr MatchKing Match ammo.

Note the rifle is zeroed at 200 yds and, accordingly, will place the 168gr Sierra MatchKing bullet 8.6" low at 300 yds. If you have a ballistic plex scope, this may well give you a 300 yd hold per the documentation. Failing that, sight in at 100 yds at 2" high, and you should hit 8-9" low at 300 yds. I personally would rather use my ballistic plex features with a rangefinder than screw around with the elevation knob with a 300 yd shot but that's my preference; ymmv.

FH

EDIT: I have my .308 and .30-06 zeroed at 200 yds, as I do with my Garands and M1As

 

[RedneckFur]

Thanks for the advice, everyone. I think I'm getting an understanding of what I need to do now. Next time I can get to the range, i'll raise my zero 2 inches and then try shooting at 300 yards to see how much more elevation I need.

Presently, I think I have about 10 to 15 inches of upward travel left in my scope, at 100 yards, that is.

 

[sneaky pete]

Let us Know !!

Sneaky Pete back: Just out of curiousity--Let us know how many 1/8 MOA "Clicks" you finally came up to zreo @ 300. THANX--SNEAKY

 

[edward hogan]

Every click value on any scope that registers movement at 100 yards or meters increases by the factor of the distance you are shooting.

IE with 1/8" clicks, at 800 yds each click moves bullet impact/reticle 1".

If you want more "range of adjustment" from your scope, IE to use the full 40moa range of reticle movement, you need a 20moa canted scope base, or a set of Burris Signature ZEE rings with their special insert liners that allow you to cant your scope.

If you have a Duplex or other "ranging" reticle with mil-dots or hash marks, you can sight-in to use the top of the thin wire area as your 100yd zero, the middle as probably a 350yd zero and the bottom as 500yd zero. Or do 50/250/400, however it works out with your handloads.

Study up some on what a "Battle sight zero" is. You will see that by sighting in to use your handloads trajectory curve within the BSZ, you don't have to worry much about dialing or holdovers if you are hunting or making a snapshot.

 

[GeauxTide]

+1 jmr40

Don't complicate the obvious. You'll probably be around 8-10 inches low at 300 with a 100 yd zero. For grins, shoot at 200 too.

 

[BobbyT]

Get yourself a .22 Eargesplitten Loudenboomer. It's a .378 Weatherby Magnum necked down to a .22.

At 5000fps, no bullet drop calculation required