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Discussion Starter · #1 ·
Hey all,

We had a discussion going in another thread that started leaning to the questions in the title of this thread. So to stay on topic I ask those questions.

First a red dot sight I contend is like using a shotgun bead and should be mounted as far down the end of the barrel as possible (in the case of a rifle) scout style so to speak. Another poster suggest that mounting more like a conventional scope will not effect accuracy, and lets be serious it is easier to mount that way.

I believe that since a red dot is just a light being projected onto a single piece of glass, it is not the same as a scope and as a result the shorter the distance from your eye the more possible error in alignment on the target. Keep in mind we are talking about non-magmifing red dot scope, not a rifle scope with an ilumanted reticle.

Tell us your thoughts and ideas!

Dave Z.
 

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I have not used a Red Dot sight on either a rifle or shotgun, but I do have one mounted on my Buckmark. The bullets go where that red dot is, whether I use a one hand, two hand, left hand, or any other type of grip and whether to dot is in the middle of the tube or off toward the side... I have no spot weld since there isn't a stock and the scope is out at arms length. I love the way it works but went with a larger tube which helps with target acquisition...or maybe I should say it helps me find the red dot inside the tube. I'd like one without the tube but they are more than I'm willing to spend. Anyway, if you compare the use on a pistol it puts the sight nearly where it would be mounted scout style on a rifle and a smaller tube should be of little concern since you would have the stock to press your cheek against and provide for very easy alignment of your eye to locate that dot. I held my pistol up close a few times just for chuckles and didn't like it at all. If I put one on a rifle it would definitely be scout style.

I can see no particular reason it would not work either way, but it easier to see that dot clearly if it's some distance from your eye. Also, the size of the dot is rather large if right in front of your eye, which to me does not make it easy to aim as precisely.
 

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In the other thread, someone said:

>>>>The red dot will shoot poa wherever the dot is within the tube, it doesn't have to be centered. This lack of parallax is one of the selling points of the red dot......<<<<

Well....... not ALL red dots......

This may be true of some of the more expensive ones, I can't say one way or the other, since I've never owned (or shot with) an Aimpoint or other "high-end" one......

However, I have a $90 Tasco PDP 5 with 4 dot sizes...... 3, 5, 10, 15 MOA...... and it definitely DOES have parallax error..... I've proven that to myself shooting off the bench.

On an accurate bolt action rifle, off sandbags, set on the smallest dot, I've shot some pretty good groups at 50, and some at 25 that amazed me! (considering).... then for kicks-and-giggles, I shot some with the dot off-center, and the POI moved..... parallax!

Then, I've mounted it as far forward as I could get it on a 10/22 with Power Custom over-the-barrel Weaver-style base, and also as far back as I could on the same base. I like it best at the back.

Because this particular sight does have parallax error, I feel it is much better to have it mounted closer to the eye..... it's easier and more natural to center the dot in the sight that way..... and, as ccw1911 said, there's much faster target acquisition that way, too (for me, anyway).

And, it's still fairly easy to hit a pistol-silhouette-sized RAM at 100 with it off-hand, if ya hold your mouth just right! (and hold over about 4-5 inches) ;)

JMHO....... gb
 

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I should've said relatively parallax free. I was using that example to make the point that there is more to a red dot sight than a bead on a shotgun. I have seen more or less parallax in cheap and expensive sights but the expensive ones are better overall.

Th point made about the dot being bigger when the scope is closer to your eye is valid for sure. A sight with a 10 min dot is huge when you get it close to your eye. Hmm, I wonder what distance from the eye the manufactors use to determine the advertised dot size.
 

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Discussion Starter · #6 ·
My point about a red dot being like a shotgun bead relates to the relationship between your line of sight and the line of the bore. We know with open/iron sights that the longer the sight radius, the easier it is to keep the two aligned, less error is invovled. Now of course there isn't a rear sight, but that does not change the fact that there is still a line of sight between the eye and the dot projected on the focal plane. With a dot mounted scout style, losing the dot is also reduced and parralax is less of a factor. As far as dot size, yes the closer to your eye the larger the dot appears and the more it covers on the target. I would also contend that tracking a target is much easier when mounted scout style, keep in mind you keep both eyes open when shooting the dot.

I've been using red dots/optical sights/dotscopes how ever you choose to discribe them since about 1988 when I put a Aimpoint 1000 on a Browning Buckmark for bullseye use. 3 different IPSC pistols with them and I've mounted them on 3 different rifles and 1 shotgun. I did mount one on a 10/22 back in 1995 as a conventional scope. True for rabbits at 25 yards it might be OK, but any distance further than that, accuracy will drop off to a point that the rabbit is gonna live another day. I used some bulk weaver rail that I got from brownells that was around 18"s, used the factory mounting holes with it hanging about 10 or 12 inches out over the barrel, then used a spacer between the barrel and the mount (made from a block of aluminum that clamped around the barrel and screwed to the rail). Mounting the Tasco PDP3 at the very end of that rail increased acceptable accuracy out to 50 yards rather than 25. It was an ugly setup, but it was quite effective.

Dave Z.
 

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Well I have to say, this thread has really piqued my interest in red dots and their various characteristics. :)

And as a qualifier/disclaimer, though, this PDP5 is the only one I've ever owned or used. Also, I always use it with both eyes open, I'm strongly right-eye dominate, so that works well for me.

It is currently riding on my 6 7/8 MkII gvt., so I got it out to "play with". I set it on the 5 MOA dot size, held it out at arms length, put the dot on a light switch across the room, and slowly moved it backwards 'til it was literally touching my brow, repeated several times. Then did it again on 10 MOA. This got me even more curious, so I printed a 3" circle in the middle of a blank page, put it up at 50 yds, put the pistol in a rabbit-ear sand bag and positioned the dot centered in the circle, and moved back and forth from the sight.....

and the dot:

1) Covered exactly the same amount of the switchcover (and the inside of the circle) at arms length as it did all the way back to my eye, so MOA coverage remained constant, no matter the distance of the sight from the eye.

2) Did not look bigger as I drew it backwards, it actually seemed to get apparently smaller (and sharper) . I imagine this was an "optical illusion" of sorts, since it was only smaller "relative" to the growing size of the tube I was looking thru, as the tube came closer to my eye. And the "getting sharper" is probably just a matter of my eyesight (nearsighted, but corrected with glasses).

I'm still trying to "wrap my mind around" the concept of farther away having less parallax, and being more accurate, but in that case I will defer to the gentlemen with much more actual experience than I.

I keep closing my eyes and imagining a shotgun with first a 2, then 4, then 6 foot barrel with a single bead at the muzzle, and I think I "get it"?!?!? :confused:
 

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Discussion Starter · #8 ·
georgiaboy said:
1) Covered exactly the same amount of the switchcover (and the inside of the circle) at arms length as it did all the way back to my eye, so MOA coverage remained constant, no matter the distance of the sight from the eye.

2) Did not look bigger as I drew it backwards, it actually seemed to get apparently smaller (and sharper) . I imagine this was an "optical illusion" of sorts, since it was only smaller "relative" to the growing size of the tube I was looking thru, as the tube came closer to my eye. And the "getting sharper" is probably just a matter of my eyesight (nearsighted, but corrected with glasses).
I must admit it was speculation on the size of the dot, but I would also suggest that the difference may not be enough to be noticed. It would be more of a deal as far as the distance from the target, but that of course is obvious.

I'm still trying to "wrap my mind around" the concept of farther away having less parallax, and being more accurate, but in that case I will defer to the gentlemen with much more actual experience than I.

I keep closing my eyes and imagining a shotgun with first a 2, then 4, then 6 foot barrel with a single bead at the muzzle, and I think I "get it"?!?!? :confused:
If I said that the parallax would change, that was not what I meant. To be a little clearer its less of a factor when the red dot is further away.

What is my contention is that the alignment of your line of sight (the line between your eye and the dot) and the centerline of the barrel will have less error the further the dot is mounted from your eye. And yes, your example with the shotgun barrel works .... Yes you got it.

Dave Z.
 

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I think it doesn't matter where you mount the dot sight. My aimpoint isn't like a shotgun bead, which is appears to be (and is) 26 inches from my eyes. The effective focus plane on the Aimpoint (and by extension, the other dot sights) is about 25 feet out, IIRC. (Can't cite the source on that factoid, sorry. I obtained it when buying the Aimpoint a couple of years ago; it may have been a US Army study. Or not.)

FWIW, I've noticed no parallax at all in mine, however, and I would have if it were there. It's mounted on a Bushmaster AR-15 A3 flattop, with Rock River handle/base. The reason that's important is that the RR base comes with (nearly) standard receiver sights. You use either the Aimpoint dot, or, if it's turned off or the battery is dead, you look through the glass and line up the iron sights, shooting as if the Aimpoint wasn't present. They appear in the lower edge of the Aimpoint's field of view, in what would be real parallax territory, were it present. It isn't; the dot superimposes over the iron sights when it is turned on. Thus, I conclude, no parallax on the Aimpoint.

Jaywalker
 

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Interesting site.
Before continuing, let me assure you that slight off-center viewing with either model resulted in imperceptible errors. If a shooter keeps a consistent rock-solid hold for every shot, parallax will not be as much of a concern. But nonetheless, knowledge of the great POTENTIAL for error is useful and reinforces the values of good technique.
The author has some experimental data to back this up, so the lack of parallax in my Aimpoint probably relates to the range at which I'm shooting, and that other ranges it would be present and greater. Good info.

Finally, also, a citation for the apparent focal plane:
With the aid of a SLR camera with a rangefinder focusing screen, by viewing the dot with 24 inches of eye relief, it becomes obvious that the dots on all four models are "focused" at around 30 feet, regardless of the distance of the target.
Jaywalker
 

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Lots of good info coming out here lets keep it going. A longer sight radius will contribute to more accurate shooting because of the geometry involved, the more distance between the sights and the more precise the alignment will be. It doesn't matter how far from the eye the sights are within reason.

I still can't get my head wrapped around the concept that sitting a red dot out further will do the same as a longer sight radius. If you accept that you would have to accept that setting your sights out farther from your eye would improve your shooting. (while keeping the same sight radius) I'm hard headed but I'm trying.

I too have been using red dot sights since they first came out. I used the first model aimpoint at the Steel Challenge in 1986. In fact my partner and I won the team match partly because I had that red dot and put it to good use on the long targets. I did some testing comparing a aimpoint to a 2 power pistol scope. Had a very accurate pistol and shot groups with the red dot and the 2 power scope. Same gun, same ammo ,same shooter, same distance 50 yds, no difference in group sizes. I did have the targets optimized for each sight though. A black bullseye for the red dot that the dot just fit inside and a bullseye with white center for the scope. It proved the accuracy of a red dot for me. whoops I'm thread drifting here, the sights where all mounted to the rear of the pistol.
 

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ccw1911, I see two issues in this thread regarding the dot sight - that of the presence/absence or parallax and that of the mount location for the dot sight.

There apparently is parallax, though less in those units that attempt to compensate for it by curving their lenses. In a use firearm, this may be more a theoretical issue than real, since my aiming errors, bullet variance, etc., are likely to be part of the set of errors that make up the group size, with the greatest errors opening the group, and the smaller errors likely compensating for each other a bit. Again, I haven't noticed any with the Aimpoint wnen shooting at either 50 or 100 yards, possibly because the 4MOA dot is already greater than any parallax effect.

On the other hand, I haven't seen anything here yet that indicates that the mount point makes any difference to either accuracy or to parallax. In fact, if the focal plane for the dot is at an apparent distance of 30 feet (or 24 feet, whatever), the experimenter would have to use the same process to see if it changed when he moves the mount point. The experimenter didn't do that, so we can't argue the case either way. My feeling is the dot on any given dotsight will appear slightly smaller if it's a foot farther from your eye, so this may give an impression of greater precision, but it would be more theoretical than real. Your mileage may vary.

Some of what we're referrng to as parallax may not necessarily be so, however. Using my iron sights through the Aimpoint did require me to re-zero the irons from previously when the Aimpoint was not present. The light through the Aimpoint does follow a different path now, so I can't just remove the Aimpoint and expect the irons to shoot to the same point of aim. This changed point of impact isn't parallax, of course, but it's real.

Jaywalker
 

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I think if the dot is focused to seem optically at 30 feet that would explain why having it close to your eye or in a scout mount would give the same size apparent dot. It wouldn't be quite the same
but it is like have this little dot 30 feet 4 inches away with a close mounting or 31 ft 6 inches away with a scout mounting. The angular difference between these two is neglible.

The difference in parallex with close and scout mount would likely be with smaller parallex in the scout mount. Because being on the edge of the view from 18 inches away is a smaller angle than being at the edge of view from 4 inches away. Though again the
difference might be close to neglible.
 

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SCOUT MOUNT

I shortened a M1 Garand 5 3/4" and "scout mounted" a PDP5 just ahead of the chamber area on the barrel. I use this setup in a tactical / defensive shooting scenario and am very pleased with it.
I have shot it on the bench to establish a sighting trajectory, and wasn't able to determine any paralax effect. BTW, shooting this setup both eyes open, allows very fast target aquisition and excellant accuracy on man targets. Willy
 
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