Ballistics Apps and Scope Zero

[D.B. Cooper]

So I just finished zeroeing my scope on a new one-piece base and rings. (DNZ Game Reaper) I set zero dead on at 100 yrds (because that's all my local range has) using factory loaded, old-school, cup and core Winchester Super-X 100 grn ammo. (.243 Win).

I'm using the Winchester ballistics app on my iPod. I set sight height at 0.9" (actual is 0.92, but the app only does 0.1" increments) with a 100 yrd zero, it shows a bullet drop of 3.9" at 200 yrds.

SOOO. Correct me if I'm wrong...but I should be able to simply adjust my scope by raising it up about 16 clicks (4") and be pretty close to dead on. Correct?

If so, then that means, using my scope's bullet drop compensator, I should be close to dead on all along the scale. (200 yrd zero on the crosshairs, next mark down is 300, and the next is 400)

I would prefer to actually fire ammo at targets at those ranges but that probably won't be an option.

I hate leaving something like this to math, so...someone check my math.

 

[stoky]

IMHO, somethings not right.
I think the sight height is suppose to be from the center of the bore to the center of the scope. 0,9 sounds low.
Zeroed at 100yds, the drop at two hundred should only be 3.3".
Are you using actual measured velocity in your calculations?
The point blank range for an 6" target for this cartridge is 283 yards. If you can only sight in at 100yds, I'd figure out how high it would be at 100 and sight it in that high there.
Arbitrary BDC can be problematic. I don't trust them with out verifying with live fire.

 

[Art Eatman]

The 100-grain .243 is about the same as a 150-grain '06. (And many other "deer cartridges.")

Two inches high at 100 is about dead-on at 200. About six inches low at 300. Roughly two feet low at 400 and four feet low at 500.

So, from a 100-yard zero, come up two inches. Since most deer are killed inside of 200 yards, you're certainly good to 250 without having to think. "Point it and pull, Hell ain't half-full."

 

[D.B. Cooper]

I derived a 0.9" sight height from data from the scope base manufacturer, and that is from the top of the receiver, so if the app wants height from center of bore, I'm pretty much screwed there-I don't know how I could accurately measure that.

I plan to hunt caribou out on the open tundra, so a 300 yard shot is well with the realm of possibilities.

I agree with Art, there must be some similarities in calibers (243/30-06) because the scope manufacturer (Redfield) uses the same 3 aiming points on the reticle for the same 3 yardages (300, 400, 500) for a broad list of calibers-essentially "non magnum" and then another list of yardages (400, 500, 600) for "magnum" cartridges.

 

[Bart B.]

so if the app wants height from center of bore, I'm pretty much screwed there-I don't know how I could accurately measure that.

Use a caliper or ruler on the side of the rifle to measure from the center of the bolt up to the center of the scope. It'll be about 1.5", +/- 1/10th inch is close enough.

 

[jmr40]

Will be close, but I'd not shoot at game much farther than I'd actually shot at the range. Most likely close enough for 200 yard shots, but things could be a lot different at longer ranges. .9" isn't right. Most scopes are going to be about 1.5" above the bore.

Run the numbers on a ballistics calculator. I use this, but there are others. This shows drops in inches, MOA, and Mils. You can use either method to compensate.

http://www.hornady.com/ballistics-resource/ballistics-calculator

If you know the exact muzzle velocity you are actually getting with your rifle the numbers will be more accurate. Having the exact BC of the bullet helps. Winchester shows that load at 2950 fps at the muzzle with a 24" barrel. In my experience stated numbers vary a lot, some are very close, others are as much as 200 fps slower. Real world speeds from a 22" barrel will be 2850-2900 fps. I can't find the exact BC on that bullet, but a similar Hornady bullet is .405.

When I plugged in that BC with 2900 fps I came up with 3.4" low at 200, so 13 or 14 clicks should be pretty close. But if the BC or actual velocity is way off as you start getting out to 300+ yards the numbers change significantly.

There is nothing wrong with a bullet compensating scope, I much prefer something like that over the archaic point blank range method. I don't like having my rifles 2-3" high at 100 yards. It is too easy to shoot over something at close range where 95% of shots are taken and it offers very little help on longer shots. On a hunting rifle I prefer the simplicity of a scope with multiple aiming points over twisting dials. Both work, but you still need to actually shoot at the longer ranges. It is normal to find that a 200 yard setting on the scope is actually a 190-225 yard zero. You'll find the same at 300, 400, and beyond.

As long as you know where you're hitting in relation to the aiming point being 2-4" above or below the actual aiming point isn't terrible hard to compensate for at extended ranges. It is a lot better than a scope with a single aiming point and no adjustment dials and having to aim 20-30" above the aiming point at long range. Certainly no harder than having to remember to aim 2-3" low at 100 yards with the older methods.

 

[ford8nr]

16 clicks on a 1/4" per click scope is 4" at 100 ( 8" at 200 )
Come up 8 clicks for +4" at 200

 

[Varminterror]

if the app wants height from center of bore, I'm pretty much screwed there-I don't know how I could accurately measure that.

Lots of pretty simple options for measuring optic height - and you don't need to be precise down to the thousandths. You're probably over-thinking this.

1) Without the optic or rings installed, lay the rifle on its back, flat across the mounts. Stack a bunch of printer paper or playing card shims under the barrel until you find the gap from the benchtop to the barrel, and measure the height of the stack. Measure the OD of the barrel, and divide by two, then add that to the height of the paper shims. Add the height from your ring manufacturer from top of base to the center of the scope (or the height of the ring from top of base to bottom of tube, then add half of your tube diameter).

2) Pull the action from the stock, measure the distance from the bottom of the barrel to the top of the scope objective bell. Measure the OD of the scope objective bell. Measure the diameter of the barrel at the same point you measured in the first. Divide the OD of the scope in half. Divide the OD of the barrel in half. Subtract both halves from the total O-O measurement.

3) Pull the action from the stock, slide playing card or printer paper shims between the scope objective bell and the barrel until they fit tightly. Measure the stack. Measure the barrel at the same point of the shim contact. Measure the OD of the scope. Divide both OD's in half. Add both halves to the thickness of the shim stack.

4) Hold the rifle vertical, trued with a spirit level. Hang a plumb line, or use a laser scathing down the side of the barrel to indicate on the stock the centerline of the bore. Mark with a tape-line the centerline on the stock. Lay the rifle 90* flat on its side, mark the centerline of the optic. Measure an "eyeballed" distance from center of optic to center of barrel.

5) Before the optic is zeroed - optically center the scope in the mirror, mount in the rings. Run a laser boresighter down the barrel, and use a collimating grid or tape measure on the wall to determine the offset from the reticle to the laser dot.

And the list of options goes on and on...

 

[ford8nr]

None of that matters if his come up is 4" off.

 

[Bart B.]

Varminterror, ain't that a bit complex compared to my post #5?

 

[Orcon]

You're somewhat limited on range but you could shoot 3 points and build your curve from there.

Lots of pretty simple options for measuring optic height - and you don't need to be precise down to the thousandths. You're probably over-thinking this.

1) Without the optic or rings installed, lay the rifle on its back, flat across the mounts. Stack a bunch of printer paper or playing card shims under the barrel until you find the gap from the benchtop to the barrel, and measure the height of the stack. Measure the OD of the barrel, and divide by two, then add that to the height of the paper shims. Add the height from your ring manufacturer from top of base to the center of the scope (or the height of the ring from top of base to bottom of tube, then add half of your tube diameter).

2) Pull the action from the stock, measure the distance from the bottom of the barrel to the top of the scope objective bell. Measure the OD of the scope objective bell. Measure the diameter of the barrel at the same point you measured in the first. Divide the OD of the scope in half. Divide the OD of the barrel in half. Subtract both halves from the total O-O measurement.

3) Pull the action from the stock, slide playing card or printer paper shims between the scope objective bell and the barrel until they fit tightly. Measure the stack. Measure the barrel at the same point of the shim contact. Measure the OD of the scope. Divide both OD's in half. Add both halves to the thickness of the shim stack.

4) Hold the rifle vertical, trued with a spirit level. Hang a plumb line, or use a laser scathing down the side of the barrel to indicate on the stock the centerline of the bore. Mark with a tape-line the centerline on the stock. Lay the rifle 90* flat on its side, mark the centerline of the optic. Measure an "eyeballed" distance from center of optic to center of barrel.

5) Before the optic is zeroed - optically center the scope in the mirror, mount in the rings. Run a laser boresighter down the barrel, and use a collimating grid or tape measure on the wall to determine the offset from the reticle to the laser dot.

And the list of options goes on and on...

You could also hire a team of engineers and a slew of statisticians, soothsayers and witchers. Probably wouldn't give you a straight answer but at least you could say you did your best.

 

[Varminterror]

Varminterror, ain't that a bit complex compared to my post #5?

You could also hire a team of engineers and a slew of statisticians, soothsayers and witchers. Probably wouldn't give you a straight answer but at least you could say you did your best.

It seems as though neither of you actually read the post.

There are 5 different options, not 5 independent steps - multiple of which are almost identical to what you described in your post, although slightly more precise, @Bart B.

The guy asked for a way to accurately measure it, not a way to eyeball it. I gave 5 options for anything between eyeballing and effectively micrometer precision.

 

[D.B. Cooper]

16 clicks on a 1/4" per click scope is 4" at 100 ( 8" at 200 )
Come up 8 clicks for +4" at 200

And THAT'S why I say "check my math."

 

[D.B. Cooper]

Actually shooting at over 300 yards isn't going to be possible. There isn't a range in the state that has a lane longer than 300, and only one in the state with a 300 yrd lane.

What do all these southeast hunters do who take these expensive trips out west? They know they'll be shooting hundreds of yards, but only have 100 yrd ranges in the populated cities. There must e some way to do this in a dependable manner without long range shooting facilities.

 

[HB]

I would sight it in 2" high at 100 and shoot the animal. If it's really far and your guide says so, pass on the shot. If its under 300 squeeze the trigger and it won't matter.

Your ability to shoot from field positions while breathing heavily will be a much greater source of error.

I was shooting my tech-sight equipped SKS today at the range and I was the only person to fire a rifle from something other than a bench. From standing I had about a 12" group at 100 and others were impressed... I was distraught that my marksmenship had sank to such lows.

HB

 

[Orcon]

Actually shooting at over 300 yards isn't going to be possible. There isn't a range in the state that has a lane longer than 300, and only one in the state with a 300 yrd lane.

What do all these southeast hunters do who take these expensive trips out west? They know they'll be shooting hundreds of yards, but only have 100 yrd ranges in the populated cities. There must e some way to do this in a dependable manner without long range shooting facilities.

So just zero 2.5"-3" high and call it a day. You're going to want to confirm zero/MPBR when you get to where you're going anyhow. If you're in elk country, you'll be able to find a place to shoot paper to at least 300 yards.

 

[Bart B.]

It seems as though neither of you actually read the post.

I read 'em all, but still thought a bit complex and they were numbered sequential like steps in order.

Your comment is respected anyway.

 

[ford8nr]

There must e some way to do this in a dependable manner without long range shootingfacilities.

You can do it dependably on paper or with a ballistic calculator but NOTHING replaces field verification. Some guides out west will have you check zero before leaving the lodge. Remember out west you have to deal with altitude too.
You can plan a long shot, making it is a whole nother matter.
I shoot a rimfire event out to 240yds, you can calculate that shot all you want. The only people who make them consistantly are the ones who practice them at full distance.

 

[Bart B.]

D. B. Cooper,

Scope height refers to the line of sight (scope center) height above line of fire (barrel center).

 

[macgrumpy]

First of all there isn't that many guys that are shooting game past 300 yards.
Secondly, if you haven't practiced shooting at game sized targets past 300 yards then you really aren't qualified to take that kind of shot, it just isn't ethical.
And finally, as others have said, simply sight in 2.5" - 3" high at 100 yards and it will do for about 98% of the game shooting that you will do out west.

All that being said, I chuckled at how long it took before somebody realized that your elevation adjustment was off, all the experts were busy rattling off so much junk that they didn't notice your error.

Remember, MOA is an angle and that means that as the target gets farther away one MOA gets larger. At 100 yds one MOA is 1", at 200 yds one MOA is 2", and so on as the distance gets longer. So if the bullet drops 4" between 100 and 200 yards then you have to adjust the elevation by 2 MOA or 8 clicks in order to hit at 200 yards.

Oh, and to measure how high the centerline of the optic is above the centerline of the rifle bore:

1. Measure the distance between the scope tube's bottom surface to the top surface of the closed bolt - D.
   
2. Add that distance to 1/2 the diameter of the scope's tube - T.
   
3. Add that combined distance to 1/2 the diameter of the bolt's body - B.

D+T+B= height of scope's centerline above the centerline of the bore.

 

[Bart B.]

Oh, and to measure how high the centerline of the optic is above the centerline of the rifle bore:

Or like post #5 shows.

 

[macgrumpy]

Or like I described.

 

[stoky]

I would sight it in 2" high at 100 and shoot the animal. If it's really far and your guide says so, pass on the shot.
HB

Remember to tip xtra if they track wounded game 4U.

 

[pintler]

On measuring, I gotta go with Bart. You can easily eyeball to 0.1 inches holding a ruler up from barrel to scope center.

If you want to be more accurate than that, put the rifle on a surface plate and use a height gage

 

[Bart B.]

Remember to tip xtra if they track wounded game 4U.

Is "4U" the four hoof prints game animals leave on the ground that are easy to follow?