[Andrewsky]

First. Say you have a 1x Eotech and a 3x magnifier. You put the magnifier behind the Eotech and it will make the dot appear to be 3moa relative to the target.

But what if you could get a longer eye relief magnifier and put it IN FRONT of the Eotech? Would the Eotech's dot then appear to be .33moa, 1moa, or 3moa?

I'm guessing 3 moa.

Second. Say I'm in a Humvee going 50mph and I fire a 62gr bullet from my M4 Carbine directly at a Jihadist's head 300m away. By how much will my bullet miss his head? The Jihadist is at a 90 degree angle to the Humvee's direction.

[Vityaz]

Do you fire when you're at an exact 90 degree angle to him?

[Andrewsky]

The bullet's path is at a 90 degree angle to the path of the Humvee.

Guys don't overly concern yourself with air resistance.

[Snake Eyes]

First, "Haji" is a racial slur to which I object. Definitely NOT High Road.

Second, to do the math on the bullet, we would have to know how fast the bullet is traveling.

[Vityaz]

If it's standard M855, I'm guessing it would be roughly 3100fps.

[Vityaz]

I think I have the answer. I'll just wait to see if anyone else gets it so I don't feel like an idiot if it's wrong. :D

Oh, and for the first question, I'm saying it would appear to be .33moa in relation to the target.

[Vermont]

I used this page for velocity info. I don't know how accurate it is.
http://www.ak-47.net/ammo/ss109.txt


muzzle velocity of round: 3100fps
velocity at 300m: 2115 fps

I'm just gonna average those two to get the average speed. It's not exactly accurate, but I dare anyone to do better.

(3100fps+2115fps)/2 = 2607.5 fps

300m = about 375 feet

375f/2607.5fps = .1438 seconds = time to travel 300m

how far will the bullet travel laterally in .1438 seconds?
50 mph = 73.333 fps
73.333fps*.1438seconds = 10.54 feet from the target

Approximately. The the deceleration of the bullet would probably not be linear. I also did not take into account the deceleration of the bullet in the direction the vehicle was traveling. It wouldn't be a continuous 50 mph.

This is my best guess. I haven't had to do much math lately.


I don't know enough about how red dot sights work to answer the first question. In fact, I have no idea how they work.

[Vityaz]

Yeah, I messed up somewhere. I think...

[Omnivore]

Putting the magnifier behind the EOTech magnifies both the target and the reticle by the same amount. The 1 MOA dot is a 1 MOA dot in either case-- it just looks bigger because of the magnification, same as a 1 inch target looks bigger through the magnifier, and yet it is still a one-inch target. Simple enough?

Place a magnifier in front of the EOTech and it magnifies the target, but not the dot, so now the dot is 1/3 MOA if you're using a 3x magnifier (the Aimpoint 2x reflex sights do just that, as the doubler is attached to the front of the sight, the target is magnified but the dot isn't. A 4 MOA dot then becomes a 2 MOA dot). You may also be changing your zero, in your EOTech/magnifier-in-front scenario, because if the magnifier is pointed off line-of-sight, the target will change position relative to the dot. Much better to have the magnifier behind the sight.

The bullet is traveling at the same speed as you-- 50 MPH relative to the target, at launch. The bullet's BC will slow it down, but only very slightly at that low velocity, 90 degree component, such that you could largely ignore it (wrong-- see my post below). The bullet will travel at 50 MPH right along with you, for the duration of its flight, so you'd have to aim that much "behind" the target. If the flight time is, say, 0.4 sec then it will travel about 29 feet in your direction of travel before it reaches the jihadist. 'Course one would have to practice this drive-by technique-- if someone can hit a target that small at 300 meters, from a moving vehicle, I'll be ultra impressed, that is unless you're using a long burst from a minigun.

[Vityaz]

Hmm. My answer came to 21.9 feet, but that was assuming a constant speed of 3100fps.

I got lazy...

[Eightball]

Putting the magnifier behind the EOTech magnifies both the target and the reticle by the same amount. The 1 MOA dot is a 1 MOA dot in either case-- it just looks bigger because of the magnification, same as a 1 inch target looks bigger through the magnifier, and yet it is still a one-inch target. Simple enough?I was going to say this, but he nailed it already. Took me some thinking to figure out how they did that.

[Omnivore]

I made an error: Your 50 MPH scenario would be much like you sitting still and shooting at a moving target in a 50 MPH crosswind. I said you could ignore the wind, but was totally wrong. You just have to know which way to "lead". You're bullet is moving with you at launch.

[akodo]

regarding the shot from the humvee.

The fact that you are moving is irrelevant for the 90 degree shot, assuming we are not taking into account human delay.

The target is also assumed to be stationary. Once the bullet leaves the barrel, it will fly straight and true for it's entire path, regardless of how fast or slow the shooter is traveling, or even his direction. You could take your shot then hit the ON button for your lightspeed transporter, and as long as the bullet left your barrel before the transporter moved you, it's all the same.

vermont has some great math, but it is only applicable to the insurgent needing to lead the humvee by 10 feet so the bullet and humvee arrive at the same point at the same time.

[Andrewsky]

Akodo once the bullet leaves the barrel it will move left or right at 50mph. And forward at about 3000 fps.

[Vityaz]

akodo, if you're moving in a humvee at 50mph, the bullet will already be traveling at 50mph in that direction, when you fire, it will still be going that way.

[Vityaz]

Andrewsky beat me to it...

[akodo]

an yes, you are right.

[Vityaz]

I need better internet...

[boilingleadbath]

Running "remington shoot ballistics calculator", I find that with a 50 mph crosswind the bullet deflects 69" at 300 yards; time to target is about .36 seconds.

This means that the bullet is pushed 69 inches "backwards" while it is "sliding" .36*50*(5280/3600)=318 inches "forwards". Net effect is that you have to aim 248" ahead of the target. (about 21')

(note: this calculation used remington commercial ammunition with an initial velocity of 3200 fps)

[Apachedriver]

Something to keep in mind when doing your figuring is which direction are you shooting from the vehicle. Are you firing 90 degrees out the right or out the left?

Anytime you fire out to the right or left of your direction of travel, the rounds will be affected by the effects of exterior ballistics(projectile drift and wind drift) as well as aerial ballistics(trajectory shift, port-starboard effect, and vertical plane gyroscopic effect). These various effects will cause the round to shift up, down and left or right of the target depending which side you're firing out of the vehicle.

Basically, if you're firing out the left side, port-starboard effect requires you to aim to the left of the target(to compensate for combined effects of projectile drift and trajectory drift). If firing out the right side, aim to the right of the target (projectile drift cancels out trajectory shift). Vertical plane gyroscopic effect requires you to aim higher when firing out the right side and lower when firing out the left.

Compensation for the effects increases as vehicle speed climbs, as well as the angular deflection of the firing weapon increasing from the direction of travel.

I wish I could tell you how to actually compute the effects of those but it's all computerized for my uses.

[rero360]

actually Haji is a term of reverance, it refers to someone that has made the pilgramige to Meca I believe, so while ignorant people might use the term in a derogatory way its not really.

[B.D. Turner]

I thought Haji was Johnny Quests friend.

[Conqueror]

I made an error: Your 50 MPH scenario would be much like you sitting still and shooting at a moving target in a 50 MPH crosswind. I said you could ignore the wind, but was totally wrong. You just have to know which way to "lead". You're bullet is moving with you at launch.

Not true. When shooting into a crosswind, the bullet starts out with 0 lateral velocity and is accelerated in the direction of the wind. In this case it starts out with 50mph lateral velocity INTO the wind and will be decelerated by the wind velocity, but likely not completely, so that it will still be moving into the wind by then end of its flight. Very different scenarios.

[ColinthePilot]

I've been told it means "Highly Aggressive Jihad Insurgent" but I think that was just so the Army could get away with using the term.

[Conqueror]

Indeed. Just like DIs can still call recruits "dicks" as long as they mention that it stands for "designated infantry combat killer" or something.

Just in case someone doesn't know the origin of the term, The Hajj is one of the 5 pillars of Islam and is the name of the pilgrimmage each muslim is supposed to make to Mecca during his lifetime. Pilgrims on the journey are called Hajjis.

[cdb45357]

Vermont,

I follow your logic, but 300M is not 375 ft. It's more like 990 feet. Plug that into your formula and I think you'll be very close.

[Wes Janson]

Running "remington shoot ballistics calculator", I find that with a 50 mph crosswind the bullet deflects 69" at 300 yards; time to target is about .36 seconds.

This means that the bullet is pushed 69 inches "backwards" while it is "sliding" .36*50*(5280/3600)=318 inches "forwards". Net effect is that you have to aim 248" ahead of the target. (about 21')

The problem with the crosswind calculations is that they're assuming a continuous lateral acceleration, whereas from the humvee it's an initial velocity only.

[Apachedriver]

Just in case someone doesn't know the origin of the term, The Hajj is one of the 5 pillars of Islam and is the name of the pilgrimmage each muslim is supposed to make to Mecca during his lifetime. Pilgrims on the journey are called Hajjis.

Conqueror is right on the money with his explanation of the original definition above.


I've been told it means "Highly Aggressive Jihad Insurgent" but I think that was just so the Army could get away with using the term.

Not true. That's an after-the-fact made up acronym.

The Army officially does not allow the use of the term "Haji" and several others. Since 2003, it considers the word to be a racial slur due to the context in which it is generally employed. There are policy letters and memos out addressing the issue.

Anyway, back to your regularly scheduled posting topic.

[TexasRifleman]

I thought Haji was Johnny Quests friend.

Johnny Quests friend was named Hadji, different spelling.

Original concept drawing from Hanna Barbera, 1964:

http://www.classicjq.com/art/production/images/HadjiHeadModel3.jpg

[Andrewsky]

Well, I think it's flat-out ridiculous that I can't say Haji.

You guys probably won't let me say "Cong" either if I ask about M60s in Vietnam.:scrutiny:

Edit: I don't mean any disrespect to the website and I know that I'm here because you allow me to be here and my membership can be revoked at any time.

[TexasRifleman]

Cong would be a legitimate reference since the Viet Nam Cong San (Vietnamese Communists) is the proper name of that group.

While Wikipedia shows "Viet Cong" to be a derogative term it is the only reference that seems to do that. Wiki also claims that the term was invented by the US Information Agency, but again is the only reference to do that.


This is quite the thread drift :)

[Zak Smith]

You can use existing ballistic calculators to solve the "moving shooter" problem by transforming the problem to this:

1. crosswind of 50 mph, with a
2. target translation of the flight time x 50 mph.

For 300 yards, the answer is 25 mils of reverse lead, which is about 22 feet.
-z

ETA:

Also, here is an OLD thread about the same topic
http://www.thehighroad.org/showthread.php?t=58101&highlight=translation

[Vityaz]

Looks like my guess was closer than I thought. :)

[W.E.G.]

I thought "Cong" was some mysterious thing that "gone bad" in the Chili Peppers' "Soul to Squeeze" tune.

Doo doo doo doo dingle zing a dong bone,
Ba-di ba-da ba-zumba crunga cong gone bad

I guess that makes some sense if it pertains to something that happened to an M60.

[Vermont]

Vermont,

I follow your logic, but 300M is not 375 ft. It's more like 990 feet. Plug that into your formula and I think you'll be very close.


Darn! I knew I would do something like that. I meant 975 feet (I approximated a meter to 39 inches). The dumb mistakes always get me. I never feel stupider than when I try to do math. Thanks for catching that.

[slogfilet]

Can we assume the rifle is zeroed at 300m? If so, then we need only find the horizontal vecor (how "wide" the shot is) and we can ignore the vertical vector (the drop.)

The distance we miss by will be the magnitude of the addition of the horizontal and vertical vectors:

A(x) + B(y) = M(x,y)

(A^2 + B^2) ^(1/2) = M, where M is the distance we miss by.

Or something.

[Wes Janson]

Zak, are we sure that crosswind gives the precise same offset as does a starting sideways velocity component? I'm unsure here, because the crosswind scenario is a constant acceleration, while the moving platform is only an initial. I'm thinking that the crosswind might give an exaggerated answer when applied to moving platform.

[Zak Smith]

Read the old thread and see if you aren't convinced...