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MichaelDiggs

Red Dot moving the bullet? :)

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I have my Aimpoint red dot zeroed in perfectly at 25 yards. I finally got the chance to shoot my second rifle outside at 50 yards. Red dot easily seen, but EVERY hole was a few inches above where the red dot was at. I know there must be a technical explanation on this and if I set my red dot below where I want the bullet to go it will go into the bulls eye. Is there a good site I can read on the technical aspects on how all that works? I didn't think a difference of 25 yards would be so great, and I certainly do not nor expect everyone zeroes their red dot all the time if they change distances. Just looking to learn and understand better.

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Red dot moving the bullet?

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:p 

 

Ok. Look at this chart that describes the flight of your bullet at different zeroing distances:

Yxj8O0T.jpg

Note: The dotted horizontal blue line marked 0.0 represents your line of sight. The colored arcs represent the path the bullet takes.

 

The red dot doesn’t move the bullet.

The dot represent where your line of sight and the path of your bullet intersect in space at a given distance from the muzzle.

See, the instant you press the trigger, gravity starts working to make your bullet fall to the ground. 

Hold a bullet in your hand and extend your arm parallel to the ground. Now drop the bullet. The amount of time it takes the bullet to hit the ground is the same as if you fired it from a rifle (if the muzzle was perfectly parallel to the ground).

To counter this, so we can shoot further, we adjust the sights to angle the barrel so it isn’t parallel to the ground. This angle gives the bullet a ballistic trajectory.

Your eyes to not see on a ballistic trajectory, they see in a straight line.

Therefore your line of sight (which is a straight line) and the path of your bullet (which is an arc) are not the same.

The bullet, will intersect the line of sight 2 times - once while rising (because the sights are above the muzzle) and once while falling.

With a 25 yard zero, the bullet is still rising the first time it crosses your line of sight and will continue to rise until about 225 yards - where it will be almost 8.5” above your line of sight (that means if you want to hit something 225 yards away, you have to aim 8.5” low). After reaching its maximum ordinate at 225 yards, the bullet will start to fall and cross your line of sight again at about 375 yards.

All this should tell you is that a 25 yard zero sucks for anything other than shooting 25 yards.

I have found that the 50yard zero is the most useful for a shooting an AR.

Zero at 50 yards and your bullet will intersect with your line of sight at 50 yards (while rising), maximum ordinate will be reached at about 130 yards and only be about 2” high, then start to fall crossing your line of sight again at 200 yards. Much more useful. You put the dot on the target and you will hit within +/- 2” from 25 to 225 yards. 

Mechanical offset will still rear its ugly head inside 25 yards and you will have to adjust accordingly - but that is regardless of zero.

 

*This is all considering you are using  a red dot optic on an AR type platform.

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IF I were a red dot shooter, I would choose the 100yd zero. Seems to be the best overall for real world shooting. 

My eyes work best with a low power magnified optic, such as a 3x or 4x ACOG, and it happens to match my rifle needs best. 

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HE's explanation is good. bullets are not laser beams. 

silverado's graphic is conceptually near, except the 25 yard zero dot is gray, and doesn't appear to actually move on the target over distance, which is wrong. Plugging it in now, the 300 yard dot is wrong too as at 25 yards, you are still fighting sight offset and it would only be about an inch high. It's more or less right for 50 and 100 yard zeros though. 

IMO MV over 3200? Maybe 100 yard zero. MV under 3200, use a 50 yard zero. 

50

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Before we get that technical remember this basic about rifle sites:   The red dot sit a couple of inches HIGHER than the barrel.   Pistols are not like that.   Just imagine if your dot or sites was perfectly horizontal, and If the bullet came out horizontal and defied gravity then every hole would be a couple inches below the bullseye.   So: to account for this you want the bullet to “rise” a little bit (or you want your sites to angle down a little bit) but really is the former because of gravity but bear with me because I’m just trying to get you to understand height differences between sites and barrels.

so that is a good explanation of why of course at 50 yards you are not hitting the same spot as 25.  Because your barrel angle is never coming out straight from the beginning. 

If you are a bullseye pistol shooter and then start getting into rifles it is a real mind fuck trying to process how you have your rifle sites on the bullseye but the bullet doesn’t go there at different ranges.  Those sites being HIGHER than the barrel is a real predicament if your goal is to hit the little red target only.  

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10 hours ago, Barms said:

Before we get that technical remember this basic about rifle sites:   The red dot sit a couple of inches HIGHER than the barrel.   Pistols are not like that.   Just imagine if your dot or sites was perfectly horizontal, and If the bullet came out horizontal and defied gravity then every hole would be a couple inches below the bullseye.   So: to account for this you want the bullet to “rise” a little bit (or you want your sites to angle down a little bit) but really is the former because of gravity but bear with me because I’m just trying to get you to understand height differences between sites and barrels.

so that is a good explanation of why of course at 50 yards you are not hitting the same spot as 25.  Because your barrel angle is never coming out straight from the beginning. 

If you are a bullseye pistol shooter and then start getting into rifles it is a real mind fuck trying to process how you have your rifle sites on the bullseye but the bullet doesn’t go there at different ranges.  Those sites being HIGHER than the barrel is a real predicament if your goal is to hit the little red target only.  

All firearms have a bore line/sight line discrepancy - often referred to as “mechanical offset” - and if you are using them for self defense, you should understand that.

My stock Glocks with standard height sights it is just a bit over .5”, on the Glocks with suppressor height sights and mini RDS mounted, it’s a bit higher still.

•••Again, the below commentary is for red dot shooting with “combat” accuracy standards - not precision bullseye or “sniping”•••

Barms, It ain’t a mindfuck unless you think about it the way you are thinking about it. The bullet doesn’t rise. Due to the angle of the barrel in relation to the sights, it has a trajectory - a flight path that will intersect your line of sight two times: once on the way up, and once on the way down. That’s the simplest way to think about it.

Except for those two times, the bullet will never, ever, ever, hit your exact point of aim. It will always be a little high or a little low. 

You need to know the distance for both of your intersection points, your maximum deviation over the line of sight and at what distance you will encounter it, and how fast it drops after the second intersection. This last part lets you figure holdovers for longer ranges - for example, I know with my 50 yard zero that to hit the chest at 300 yards, I need to aim for the neck, at 400 yards, above the eyes.

With an appropriate and useful zero distance, your maximum deviations should be minimal at the ranges you are most likely to encounter. This allows you to not have to think about changing your point of aim for as long as possible.

This is why I like the 50 yard zero. If I do my part, I will never be more than 1.75” high to 1” low from 25-225 yards*. For all intents and purposes - that is point of aim for social engagements.

From 0-25 yards you need to account for mechanical offset regardless of your zero - if you are taking a high percentage shot. 

The offset will alway be equal to the distance between the center of your bore and your aiming point at 0 yards and decrease logarithmically from there until you reach your first intersection point or zero distance.

If I need to take a precision shot inside 25 yards, with my preferred 50 yard zero, I know I have to place my dot about 2.5” above my intended point of impact if I am 7 yards and in. I place the dot about 2” high from 15 yards to 7, and about 1.5” from 15 yards to 25 yards and about an inch at 25 yards.

Keeping these numbers in mind, I can estimate anywhere in between if I can gauge my distance to target appropriately. For example - If I am closer to 25 yards, my holdover is closer to 1”, if I am closer to 15 yards away, I hold closer to 1.5” high at 20 yards, I’ll split the difference and try to put my dot 1.25” above my intended point of impact.

I also know that I find a 1” group at 25 acceptable so that’s why I only care about offset inside 25 yards. At around 130 yards I will have the maximum height over line of sight at around 1.5”ish. I am fine with a 4” group there, so I don’t change my aiming point.

So, say my target is an 8” circle. If I aim dead center of it, I will never be more than:

• 2.5”low of center at 0 yards,

• Dead in at 50yards

• 1.5” high of center at 130 yards

• Dead on at 200ish yards 

• 2” low of center at 250 yards.

These are all well inside my acceptable hit area of an 8” circle considering a 4” radius.

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30 minutes ago, vladtepes said:

50 yard zero for an AR all day long.. as stated.. 50 and 200 intersect.. and my typical AR shooting is inside 200 yards... so the amount of adjustment is relatively minimal.. 

Good advice from vladtepes, as usual.  T Bill, thanks for posting that video and saving me the trouble of digging it up.  That's the best explanation I have seen of the pros and cons of different zeroes.  I refer to it every once it awhile, but mostly I'm zeroed at 50 and 200, so my POI is just a little higher at 100. 

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First, just want to mention the topic was sarcastic. I know the red dot doesn't move the bullet. And on that note I really appreciate the information all of you have explained here. It does seem that shooting in the limited 25 yard indoor ranges is what made me zero at 25 to begin with. I'll take a recommendation and try to zero at 50 yards and try that out for a while. Now I kind of know why some shooters like reticles etched glass with static information on it to help you hit a target. Hitting a bullseye at 100 yards with just a single 1x red dot would be very difficult to me. I only have a simple 3x magnifier. Thinking of looking at some Vortex scopes or dots. Have an Aimpoint now, Vortex though are all made in China I think but have a very good warranty like Primary Arms.

Thanks guys!

 

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19 minutes ago, MichaelDiggs said:

First, just want to mention the topic was sarcastic. I know the red dot doesn't move the bullet. And on that note I really appreciate the information all of you have explained here. It does seem that shooting in the limited 25 yard indoor ranges is what made me zero at 25 to begin with. I'll take a recommendation and try to zero at 50 yards and try that out for a while. Now I kind of know why some shooters like reticles etched glass with static information on it to help you hit a target. Hitting a bullseye at 100 yards with just a single 1x red dot would be very difficult to me. I only have a simple 3x magnifier. Thinking of looking at some Vortex scopes or dots. Have an Aimpoint now, Vortex though are all made in China I think but have a very good warranty like Primary Arms.

Thanks guys!

 

It rilly kinda depends on what you’re trying to do with what you have. Would you expect 1” groups at 200 with a handgun? 

I dunno, I feel like firearms fit into a color spectrum. ROYGBIF and you mix and match to a point.

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