Simple bullet drop trajectory question

[tpcollins]

I'm trying to understand hold over and trajectory on my ballistic trajectory chart. At 100 yards my poi is 1.5" high with a 131 yard zero distance. And the bullet drop is -8.3" with a -3.9 MOA (-4.15") at 200 yards. I assume if I:

- held 4.15" high at 100 yards, it would hit the bull at 200 yards,

or

- I could hold 8.3" high on the 200 yard bull and hit it (which would be 5.65"
high at 100 yards).

Thanks.

 

[PawPaw]

I'm not sure I understand the question.

At 100 yards my poi is 1.5" high with a 131 yard zero distance.

That makes sense. If you're rifle is sighted so that the impact is 1.5" high at 100 yards and you have a 131 yard zero, then the bullet will have dropped into the point of aim at 131 yards.

And the bullet drop is -8.3" with a -3.9 MOA (-4.15") at 200 yards

I don't understand where the MOA comes in, so lets disregard it. Consider that your bullet is down 8.3 inches at 200 yards, so you'll have to hold over 8.3 inches to have the bullet strike at the point of aim.

If I understand the question correctly.

 

[tpcollins]

I can't paste the entire chart but at the 200 yard line is the following data:

Range …. Drop ... Drop
yd ………... in …... MOA

200 …... -8.3" ….. 3.9


It's my understanding that the "Drop MOA" would be the same as "Clicks Up" on the vertical turret to hit the bull at 200 yards. And on it's way to the 200 yard target it would be roughly 5.65" high as it passed thru the 100 yard plane.

 

[Brian Pfleuger]

Technically, you'd be holding 4.15" high at 100 to hit the 200 yard target dead on... but why would you do that? If you want to hit the 200 yard target, you should be aiming at the 200 yard target and holding 8.3" high.

You're confusing the path of the bullet with the path of the beam of light you're using to aim. The light is going straight, only the bullet is following a curved path. Hold over is linear. 1" at 100 is 2" at 200 is 3" at 300 is 4" at 400... is 10" at 1000.

All you care about is how low the bullet is at the distance you want to hit. If it's 8" low, you aim 8" high.

 

[tpcollins]

Technically, you'd be holding 4.15" high at 100 to hit the 200 yard target dead on... but why would you do that? If you want to hit the 200 yard target, you should be aiming at the 200 yard target and holding 8.3" high./QUOTE]

Thanks Brian, that's what I'm looking for. The reason I asked the question that way is I have a 3-9x36 Swarovski with the 4A reticle. The sub-tenstion from the crosshair center to the top of the post is 8.3" at 100 yards - half of that is 4.15".

So I think if I center the target between the crosshair and the top of the post at 9x, it should smack the 200 yard target dead nuts. If I frame the target the same way but at 100 yards, it should hit that target 5.65" high but go beyond and hit the 200 yard target dead on - or at least that's my thinking . . .

 

[SSA]

This must be a slug gun or a muzzleloader. What bc and mv are you using for your calculations?
Do you want to sight it in for deer hunting?

 

[Brian Pfleuger]

it should hit that target 5.65" high but go beyond and hit the 200 yard target dead on - or at least that's my thinking . . .

Yes, if you aimed 4.15" high at 100 and you were sighted 1.5" high at 100, you'd hit 5.65" high at 100...

If you're literally referring to the SAME BULLET hitting a 100 yard target and then carrying through to a 200 yard target, it's unlikely even with paper.

 

[tpcollins]

Thanks Brian.

This must be a slug gun or a muzzleloader. What bc and mv are you using for your calculations?
Do you want to sight it in for deer hunting?/QUOTE]

Yes, I was hoping this forum could answer this for me.

.451" dia Barnes .50 cal 250 gr TMZ, BC - .210, 2000 fps, 1.4" scope height, impact is 1.5" high at 100 yards, with a 132 yard zero yardage.

- at 200 yards, drop is 8.3" with 3.9 MOA drop (16 clicks up)

- at 255 yards, drop is 21.1" with a 7.9 MOA drop (32 clicks up)



I converted the inches to MOA so it would match the JBM chart. I'd like to be able to turn the scope up to 9x and shoot a maximum of 200 yards. To me, the data indicates if I "frame" a deer's back and belly at 200 yards with the crosshair and post, I should hit it in the middle - yeah or nay?

 

[SSA]

Yeah.

Sight in dead on at 100, or maybe .5" high. That will put you within 2" out to 130 yards or so.
Using the top of the post as an aiming point, you'd be 8 or 8.5" high at 100, you'd be about 5" high at 60 yards, 9" high at 125, and 5" high at 200.
A hold with the top of the post at the bottom of the deer's chest would put the bullet between 5" and 9" up from the bottom the the deer's chest at any range from 60 to 200 yards.

 

[tpcollins]

Thanks SSA, but if I had wanted it sighted in at 100 or +.5" high at 100, I would have done that in the beginning. Thanks anyway.

 

[Brian Pfleuger]

At least for hunting purposes, I don't know anybody who zeros at 100. Typically, 0.75-1.5" high is normal, depending on cartridge and vital zone size.

 

[tpcollins]

Let me ask it this way. If I'm zeroed 1.5" high at 100 yards, and I aim 3.9 MOA high at 100 yards, that's roughly 4.15". I'm under the impression that this same 3.9 MOA at 100 yards would become 8.3" at 200 yards, correct? I think it should hit the bullseye at 200 yards then.

 

[Brian Pfleuger]

Well, it gets a lot less complicated if you pick a term and stick with it. They're the same at 100 (basically), an inch is an MOA. 1 MOA at 100 is 1.047". Most people just drop the .047 and call them the same. That's fine at 100 but that 0.047 adds up as you get farther out. It's best to just pick a term and use it. Either inches or MOA, don't mix them.

Remember, the light beam is going straight. It doubles in height when distance doubles.

MOA also doubles with doubled distance. If you're aiming 3.9 MOA high at 100, you're also aiming 3.9 MOA high at 200 but the actual amount in inches doubles.

Don't mix them up. Think in MOA or think in inches. Don't try to do both.

 

[tpcollins]

MOA also doubles with doubled distance. If you're aiming 3.9 MOA high at 100, you're also aiming 3.9 MOA high at 200 but the actual amount in inches doubles.[/QUOTE


Thanks Brian, that's exactly how I was understanding it. The only reason I was using inches and MOA is the scope's sub-tensions are in inches, the JBM chart is in MOA. So as long as I use 1.047" for one MOA, I figure I can multi-task rather easily . . . thanks again.

 

[PawPaw]

At least for hunting purposes, I don't know anybody who zeros at 100

This year, that would be me. For some reason that I can't explain, my go-to deer rifle is sighted dead-on at 100 yards. I normally sight in an inch high at 100 yards, but this year I went brain-dead during my last range session.

 

[Brian Pfleuger]

Thanks Brian, that's exactly how I was understanding it. The only reason I was using inches and MOA is the scope's sub-tensions are in inches, the JBM chart is in MOA. So as long as I use 1.047" for one MOA, I figure I can multi-task rather easily . . . thanks again.

My sentence is a little wrong up there. I said MOA doubles with doubled distance, which isn't so, it remains constant but the actual measurement doubles. I had it right in the second sentence, wrong in the first one.

I use JBM all the time, they list inches and MOA.

This year, that would be me.

I should have said "on purpose".

 

[AZAK]

At least for hunting purposes, I don't know anybody who zeros at 100.

Why not? Wouldn't it make those BDC reticles make more sense? And Mil-Dot?

The math involved in bullet flight is complex enough, especially when considering all of the different variables involved, I like having at least one standard.

All of my hunting and target centerfire rifles are zeroed at 100; with the load currently shot the most often. (I only change them if I have a specific/really good reason to do so.) I hand load, and check my loads with chronograph, BC info, charts, and then test them out in the field to bear out if they are doing "what they are supposed to do"; amazing what different temperatures can do to a load.

So, I do change my scope, but mainly for temperature differences or changing to a different "mostly used" load to bring it back to 100 yard; think temp difference between summer and Winter in Alaska, it is noticeable.

When I start "reaching out" I sometimes use those knobby things on the sides of the tube-thingy. But, mostly I know the bullet drop from 100 yards and compensate for it, either with the reticle or with turret adjustments.

The bullet is going to follow the same path, gravity being fairly constant, regardless of how one wants to view it, what matters is if the shooter understands the relationship of how he/she is viewing it to the actual flight path.

YMMV

 

[Mobuck]

I used to sight in 3" high @100 yards with everything but have shifted to around 2" with most rounds. A 2" high @100 yards will give you slightly longer point blank(hold on brown) range w/o causing you to shoot excessively high at shorter ranges. If you need a 5" high @ 100 yard sight in, you really need a longer range capable cartridge.

 

[Brian Pfleuger]

Some places you can only hunt with shotgun or muzzleloader. There aren't choices for "longer range capable cartridge".

 

[Bart B.]

So as long as I use 1.047" for one MOA, I figure I can multi-task rather easily...

I think it's easier using the original MOA subtention that started over a century ago. Mentally managing zero decimal places is a lot easier than managing three of them.

In the USA, long ago, rifle targets were established that had scoring rings even inches apart. And were shot at 100 yard increments or simple fractions thereof. So both scope and metallic sights had their adjustments such that one full unit moved impact exactly 1 inch for every hundred yards of range. And virtually all targets have scoring rings and adjustment grids on even inch spacings.

Telescopic sights with external adjustments moved .0005" per click on their 40 tpi knobs. With the 7.2" standard spacing of the two rings on bases, four clicks moved impact 1/3600th of the range. That's exactly 1 inch per hundred yards.

Iron sights had a 30" standard sight radius and their adjustment screws were also 40 tpi. One third turn of a knob moved the sight .008333" and that's exactly 1/3600th of 30 inches. They had 3 MOA per turn; exactly 1 MOA per third.

But someone learned in the late 1960's that their brand new scientific hand held calculator had trigonometry functions and they thought the rifle shooters were too out of date. But these folks didn't have any problems with the different number of yards in the different distances called "one mile" whether it was statute, nautical, radar, Scandinavian or metric miles.

I perfer the shooter's MOA over the trig one; much simpler and mentally manageable.