Need help with Reverse image zero

[Unknown]

I understand the concept of knowing your maximum ordinate so you know how far out you can hold at a certain part on a target and expect a hit. What I still have trouble grasping is why it is called reverse image zero, and it's relationship to simply knowing your trajectory, and where you can hold to expect a hit.

In the book "The complete 50 Caliber Sniper Course, on page 304, paragraph 4, the theory is explained. For years, I have used the concept of knowing the maximum ordinate, or where I can hold dead center and expect the bullet to strike either plus or minus a certain amount.

What I'm having trouble with is the whole imagine a mirror, the reverse image in the mirror and how this concept applies to maximum ordinate.

Any help with this will be greatly appreciated. Maybe I just need to get past the weird name for the theory, and accept that I know how to apply the concept.

 

[CoryT]

Re: Need help with Reverse image zero

The original thought was to zero such that you held BELOW the target by the height of the target, the standard being a standing man. Hold below his feet, as if you had an inverted image. When using something that has a trajectory like a rainbow it does extend the range at which a single hold point will hit somewhere in the height of the target, at least in theory. It never worked very well because of the problem of projecting the aim point. It's practical value with modern cartridges is almost non-existent, so it is obsolete. It's simpler and more intuitive to create a Maximum Point Blank zero that's based on the size of the target. The actual max range will be quite a bit shorter though.

The Parallel Bore Zero is also obsolete, with current computer programs doing the compensation for conditions and current zero point.

 

[Lindy]

Re: Need help with Reverse image zero

Actually, a parallel bore zero does have one use I can think of - taking a shot straight down (or up). Then all you have to do is to hold off by the height of the scope above the bore, irrespective of the distance to the target.

It's not a capability many are going to need.

 

[Unknown]

Re: Need help with Reverse image zero

Is parallel bore zero the same as reverse image zero? If so, I'm still confused.

I understand the line of sight over line of bore (trajectory), and have used it to great advantage in matches where other people don't realize that they have to compensate for that difference when shooting tiny targets from 25-90 yards.

Because I don't understand why I should consider what a reverse image of the target would look like in order to figure trajectory, the whole reverse image zero issue has me confused.

But the method of knowing how high your bullet will rise from the muzzle to point of impact (lets say 42 inches) over X distance makes perfect sense to me. The old Marine sniper manual used to teach a 500 yard zero, and had different points of hold (knees, crotch, belt, center chest, head, stomach) in order to get a hit at various distances. But the reverse image concept is different...(I think).

So, I'm hoping someone smarter than me can explain what I'm not understanding.

Thanks for thinking about the issue folks!

 

[The Mechanic]

Re: Need help with Reverse image zero

The whole point of parallel bore zero in that book was because it was written before zero stops. To answer your question no it is not the same as reverse image. Parallel bore was just a way to get to a set point on the scope that you could use as a short range zero and then use all your MET data to get a first round hit.
I'll go back and re-read that section on reverse image, as it has been several years since I read it.

 

[Unknown]

Re: Need help with Reverse image zero

The parallel bore zero part was fine...I understood that. I had trouble with the concept of how seeing a reverse image of your target at twice it's range would help.

I appreciate your help. It appears that not many people know what I'm talking about here. That sort of surprises me as I expected lots of people to have studied and understood this tactic. Is it really that advanced?

 

[CoryT]

Re: Need help with Reverse image zero

It's actually very old, first proposed around WWI for the Enfield rifle. In concept, it's much like grazing fire with an MG. The idea is to take maximum advantage of the arc to place a target SOMEPLACE in that arc.

Lindy, I still PBZ my Vickers and BREN (at least windage), since the sights are offset well left of the bore. I hadn't considered straight up/down.

 

[kraigWY]

Re: Need help with Reverse image zero

I use to teach it in machine guns schools. Gen Hatcher (then Major) wrote quite a bit about it in his book "Machine Gun's 1916. It's really handy when you are teaching indirect fire with a machine gun, but not too useful in rifle shooting, unless you can't see the target your shooting at. Then it works. We played with it when I was teaching sniper schools using M1C/Ds.

Its fun to play with, but more interesting then useful.

If anyoen is interested let me know and I'll dig up my notes with the formulas.

 

[Unknown]

Re: Need help with Reverse image zero

I understand the whole concept of using the arc of your trajectory to get a hit somewhere on the target. What I don't get is why they call it reverse image zero, and what the hell that has to do with the technique?

It would make more sense if they called it trajectory arc zero shooting or something like that.

 

[The Mechanic]

Re: Need help with Reverse image zero

The reverse image zero was made for fast unknown distance targets. It is actually kind of interesting and unique in its method.

Basically you zero the rifle for a head shot on a reverse image of the target at your farthest ballistic range. At the time it was developed that was the .303 so it was 700 yards. What is meant by reverse image is, picture a man in hovering in mid air now picture a clone of him standing on the bottom of his feet so you now have his "reverse image" upside down. You will aim at the head of the upside down man. This is shooting WAY under the target but the idea is using a type of point blank range in that the farther you go the smaller the image so you would automatically raise the muzzle and be compensating for the extra distance without having to do any figuring.

It was not designed as a precision tool it was designed as a fast target, get the shot off fast type of automatic ranging that seemed to work well on your way to your firing position. Let me know if you understand my explanation as I can get a little more "into it" by using some quotes out of the book.

 

[Unknown]

Re: Need help with Reverse image zero

Mechanic,

Your explanation is the best one so far. I am beginning to picture it. I thought that the book wanted me to picture two people with one standing on top of the other, and I aim at the base of the lower fellow's boots. Your explanation has me aiming well below the boots though.

When the book got to the 300 Win Mag, and had me aiming at the crotch, it made lots more sense, because as the book says, even the 308's drop is about half that of the 303, and the 300 Win mag is even less than that.

Maybe it is the "reverse image" part that is confusing me. I am very comfortable with the part of using the arc of the trajectory, and by knowing the arc, you know that anything within an arc of maybe 6 feet for the 308 out to either 500 or 700 yards (I can't remember which one they used) will yield a hit.

When using the 300 mag, holding on the crotch out to 500 yards will yield a hit.

So, please continue working with me on this. If you prefer to send me a PM or email, that is fine. Everything else in the book seems really easy for me to understand and utilize. This is the first thing in the book that has baffled, or stalled me. Maybe I'm just getting a brain cramp....

 

[fargo007]

Re: Need help with Reverse image zero

You're creating a sewer pipe the size of the target that the bullet will fly in and never touch the pipe. The bigger the target, the bigger pipe you get.

You are setting your scope to the bottom of the sewer pipe, at the far end.

So holding at the feet of a target at the far end, the bullet would hit that target anywhere it was inside the pipe. Maybe could be useful for a defensive engagement where there is no time to estimate range.

The PBZ is similar, except you are using a smaller pipe (and accordingly shorter distance).

Some ballistic calculators will take a radius in and provide you with the distance and correct zero point for a PBZ.

Here's a rough illustration: For a .308, set your dope to 450Y or so and shoot at IPSC size plates from 100 to 500 with a CM hold. You will hit them all.

--Fargo007

 

[magnum_99]

Re: Need help with Reverse image zero

I always imagined that the R.I.Z. would potentially be useful in an overwatch scenario where the element was predicting being advanced upon and may have to shoot and scoot, and would have to engage targets up to a predicted "danger area" of X range, with no time to actually calculate precise range and dial scopes.

You could set your max range, say 700 yards (weapon dependent) and engage any target out to that range by holding low, without needing to know the exact range.

The practical use is probably pretty limited and weapon dependent (flatter rounds would be more useful) but it may be a good way of placing strafing type fire on an advancing enemy from great distance while you also quickly fall back.

 

[The Mechanic]

Re: Need help with Reverse image zero

This particular iron sight setting is basically designed for walking to a hide and you come up on an enemy up to 700 yards and you must do a very fast engagement without ranging of any kind. As the target gets farther out your hold change will double the correction.

As you see by my Michaelangelo skills as the target gets smaller due to the range getting larger the reverse image will also get smaller so when you aim at the head of the reverse image the muzzle up correction will double because both the person and the reverse get smaller. This is supposed to give better hit probability without site adjustment of any kind.

The .300 WM was actually a different method of PBZ and was not the same method as the RIZ. Pretty much to different versions of trying to accomplish the same goal of a non adjusted sight, that is not range estimated and fast.

 

[Unknown]

Re: Need help with Reverse image zero

I liked the sewer pipe analogy, and thought I had it, as that was the way I was thinking about it. If I have a 6 foot trajectory arc, and the target is standing in a sewer pipe that is 6 feet high, I aim at his feet, and regardless of where he is, I will get a hit as long as he is within the distance (X) that has the 6 foot arc of trajectory. (somewhere between 500-700 yards or so for a 7.62x51 round)

Then seeing the next image confused me again. With the sewer pipe analogy, if my arc is 6 feet, I would aim at the feet of the actual target and get a hit somewhere on the target.

But if I use a reverse image, aren't I actually aiming 6 feet below the feet of the actual target...so I would hit some where between the feet of the actual target, and up to 6 feet below (actually in front of) the actual target? This is the part that confuses me.

The sewer pipe part was how I understood everything, but perhaps I'm making a mountain out of a mole hill as long as I understand the sewer pipe analogy.

I hate it when something that I think is this basic causes me so much mental indigestion!

 

[Lindy]

Re: Need help with Reverse image zero

Rather than the reverse image zero, I shoot everything with a precision rifle out to 600 yards from a 100 yard zero, and just hold over using the reticle, eyeball-estimating the range.

On targets of a size where a RIZ would work, so does that, and it's a lot easier to conceptualize, especially since I've already memorized the holdovers.

 

[fargo007]

Re: Need help with Reverse image zero

You ARE overthinking it.

Traditionally at distance we hold high on (or over) the target to score a hit on it.

This is the REVERSE of that traditional image.

Yes - aim at the feet and hit the feet only at the end of the sewer pipe. As that imaginary target moved inside the pipe closer to you, the impacts would rise up as it approaches, until your max ordinate, and then begin to lower as it approached from there. You would not be aiming below the target with RIZ.

Try the PBZ drill I proposed above. Doing it with a rifle at real distance will definitely switch the light on for ya.

HTH,

--Fargo007

 

[The Mechanic]

Re: Need help with Reverse image zero

The reverse image zero is a very weird way of aiming. Yes you aim WAY below the feet by exactly the height of the target. It is not the PBZ method. It was a completely different method of the PBZ except it gets you a little more range and was designed for the .303 Was not based on accurate fire just as a VERY fast way of ranged fire without purposeful ranging.

The discussion in the book had many methods or versions of PBZ type of shooting or compensating at distance without purposeful ranging.

 

[Unknown]

Re: Need help with Reverse image zero

Fargo,

Thanks so much! I thought maybe I was over thinking it, or that it was the name that was bugging me. With the way you explained it, it makes perfect sense to me. It was the name that didn't make sense, and the theory and application is really easy for me to understand.

Because I'm more of a concrete thinker than an abstract thinker, I usually think that there is some abstract concept I am having trouble with when things don't make sense easily. But the way you explain it makes perfect sense. I now know it was just the name of the concept that bugged me.

The sewer pipe part really helped. It is sort of like the point blank part of my exbal program when trying to shoot a 10 inch plate. It will tell me that at a given distance, (lets say 437 yards) with a 437 yard zero, I will strike the plate between 415 and 442 yards (for example) with a center hold.

Thanks for the input everyone. It helps to get input and know I'm not an idiot, I was just overthinking this issue.

I'm grateful for all the input.

 

[Sterling Shooter]

Re: Need help with Reverse image zero

Just an observation, shooters just starting out do not think about external ballistics/trajectory. These shooters visualize the bullet as a laser. After all, the bullet in flight is too small and fast for them to actually see it to understand the flight is a definitive and uniform arc. There have been many novel means of getting these shooters to come to come to terms with the usefulness for a battle sight zero as well as bullet drop compensation, such as comparing the bullet's flight to a football, or spinning top. As was said earlier here, this sort of stuff can be more confusing than helpful, if it's delivered by an instructor who himself is not comfortable with the material. I usually rely on graphics, just showing things like line of sight, line of bore/departure, and bullet path. These simple graphics will get most folks who have an I.Q. over 77 a clear understanding for the need to adjust aim.

 

[Unknown]

Re: Need help with Reverse image zero

I understand all the elevation concepts and usefulness of them. The mechanics of the difference between line of sight, and flight path of the bullet, MET/ENV factors seem pretty straightforward and I am able to figure all that stuff out. Once the data has been collected though, it is just a matter of basic math to figure out what will happen to the flight path of the bullet.

I think like Fargo said, I was over-thinking the issue. The concept seems pretty straightforward, I think it is the name of the concept that threw me off.

I have a scope that has ten hash marks at mil, and half mil distances on the vertical crosshair. Depending on where I have the rifle zeroed, it is really helpful to know the exact point of impact for each hash mark, and to know how much plus or minus the exact point of impact I can shoot to get a hit on a plate.

For example, if my hash mark's point of impact is 487 yards, I can reasonably expect a hit on plates from 480 to 491 yards. That concept saves alot of time dialing up or down on the elevation turret when times are tight. Sure, dialing correctly is far better, but when time is a factor, often it is better to just hold off and shoot.

 

[MGC]

Re: Need help with Reverse image zero

Great feedback. This is what we need to do on nov 13

 

[Rookie]

Re: Need help with Reverse image zero

Unknown,

Thanks for asking the question. This thread has cleared some things up for me. I remember in a sniper match when I was first getting started in LR rifle, there was a stage called, "Deep strike" that required hitting a target set at the back of a concrete culvert. I blew it but others said later something about dialing for a longer distance and holding low which would use the bullet's flatter intermediate trajectory. It now seems to make sense to me, and I think anyway, is related to your topic. Gonna spend some more time rereading this thread and doing more research.

 

[hrt4me]

Re: Need help with Reverse image zero

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: fargo007</div><div class="ubbcode-body">You're creating a sewer pipe the size of the target that the bullet will fly in and never touch the pipe. The bigger the target, the bigger pipe you get.

You are setting your scope to the bottom of the sewer pipe, at the far end.

So holding at the feet of a target at the far end, the bullet would hit that target anywhere it was inside the pipe. Maybe could be useful for a defensive engagement where there is no time to estimate range.

The PBZ is similar, except you are using a smaller pipe (and accordingly shorter distance).

Some ballistic calculators will take a radius in and provide you with the distance and correct zero point for a PBZ.

Here's a rough illustration: For a .308, set your dope to 450Y or so and shoot at IPSC size plates from 100 to 500 with a CM hold. You will hit them all.

--Fargo007</div></div>

good analogy