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Posted: 2/14/2006 11:02:39 AM EDT
Scenario: M193 ammo out of a 16" 1:9 barrel. You have a laterally moving target at some range, let's say 200M. Assume no wind effects. Your weapon is zero'd at 200M. You are traversing your weapon laterally to track the target so that the point of aim stays centered on the target (no leading). You break the shot perfectly.

Assuming you've done your job as described above, the bullet will do its thing in both the elevation and azimuth planes. M193 behavior in the elevation plane is well described and easy to find (e.g. Arfcom's own Ammo Oracle page). What I'm interested in is getting a better understanding of the bullet's behavior in the azimuth plane.

If there were no lift/drag/whatever effects and you were traversing perfectly the bullet ought to hit the target with no lead. Of course there must be some fluid dynamics involved whereby the lateral component of the bullet's velocity is affected, thereby requiring some lead on the target. The further the range the greater the lead.

Anyone know where I can get some perfomance numbers regarding this for M193?

Thanks!

aa
Link Posted: 2/14/2006 11:09:13 AM EDT
The BRM manual has the info for leads including the correct sight picture.
Link Posted: 2/14/2006 11:21:02 AM EDT

Originally Posted By aa777888-2:
Scenario: M193 ammo out of a 16" 1:9 barrel. You have a laterally moving target at some range, let's say 200M. Assume no wind effects. Your weapon is zero'd at 200M. You are traversing your weapon laterally to track the target so that the point of aim stays centered on the target (no leading). You break the shot perfectly.

Assuming you've done your job as described above, the bullet will do its thing in both the elevation and azimuth planes. M193 behavior in the elevation plane is well described and easy to find (e.g. Arfcom's own Ammo Oracle page). What I'm interested in is getting a better understanding of the bullet's behavior in the azimuth plane.

If there were no lift/drag/whatever effects and you were traversing perfectly the bullet ought to hit the target with no lead. Of course there must be some fluid dynamics involved whereby the lateral component of the bullet's velocity is affected, thereby requiring some lead on the target. The further the range the greater the lead.

Anyone know where I can get some perfomance numbers regarding this for M193?

Thanks!

aa



All of that just to ask how far do I lead a moving target? Fluid dynamics?

Btw even with all of that jumble of words you left out how fast the target was moving. Try a sniper forum. They will likely have charts available.

My guess would be roughly 1 body width of lead for a walking target at 200M.
Link Posted: 2/14/2006 11:32:12 AM EDT
This is an easy problem.

If the target is moving and the shooter is stationary, the POA must lead the intended POI. The lead distance is the (target speed) * (bullet flight time).

For example, with M855 at 3000fps from a 16" barrel, the time of flight to 200 yards is about 0.22 seconds.

A 10mph target moves 14.6 ft/second.

14.6 * 0.22 = 3.27 ft LEAD on a 10mph target @ 200 yards.

Convert to mils would be 5.46 mils @ 200 yards.

For a shooter on a moving platform shooting at a stationary target, shooting at a right angle to his direction of movement, there is reverse lead AND a "wind" component.

If the shooter is moving 10mph and shooting at a target 200 yards away, he will need 2.93 FEET reverse lead, or 4.9 mils reverse lead.
Link Posted: 2/14/2006 11:39:15 AM EDT
[Last Edit: 2/14/2006 6:17:43 PM EDT by Molon]

If there were no lift/drag/whatever effects and you were traversing perfectly the bullet ought to hit the target with no lead.


Incorrect. The instant the bullet leaves the muzzle of your rifle its trajectory is set. So while your sights were dead center on the target the instant you pulled the trigger your target continues to move laterally while the bullet is traveling down range. At 200 yards it takes an M193 round .221 seconds to reach the target (assuming a muzzle velocity of 3100 fps from a 16" barrel). In that .221 seconds a man running at say 5 mph has traveled 19.5 inches. Therefore you would need to lead your target by 19.5 inches (or about one body width as mentioned above)
Link Posted: 2/14/2006 12:22:07 PM EDT
Now, about this whole inverse lead thing where I'm moving, he's moving the opposite way, and we have a .934 angle adjustment with a 10MPH full value right wind. He's moving left, I'm moving right at 12 MPH. Range to target is 245 meters. Rifle is a 20" SPR shooting 77grain Mk262. Temperature is 86F, humidity is 34% with a 65F / 90% / sea level zero./ Current engagement is at 6200 feetASL (firing position).
Link Posted: 2/14/2006 12:26:23 PM EDT
I know you were being facetious, but here's how you'd do it:

1. use the cosine of the wind angle from "straight sideways" as the cross wind value

2. when shooting off from straight sideways, use the diagonal distance to compute the time of flight

3. To compensate for a moving target also, when also shooting from a moving platform, you would add or subtract the normal "lead" data from/to the reverse-lead data.
Link Posted: 2/14/2006 12:30:42 PM EDT

Originally Posted By Molon:

If there were no lift/drag/whatever effects and you were traversing perfectly the bullet ought to hit the target with no lead.


Incorrect. The instant the bullet leaves the muzzle of your rifle its trajectory is set.



Aaargh. You're right, Molon, I don't know what I was thinking. My traverse amounts to a lateral velocity of a fart in a windstorm (inches per second at best). I don't know what I was thinking!

(I'll beat myself with a chair later)

Sorry to waste all your time and bandwidth!

Or, in the words of a famous Saturday night personality, "Nevermind!"

aa
Link Posted: 2/14/2006 12:51:58 PM EDT
[Last Edit: 2/14/2006 12:53:52 PM EDT by 200-10x]
Well, it was fun to read, anyway..... lol

On a more practical note... for all the talk here about this gear and that gear and this cartridge and that cartridge, and chrome-lined vs non.....THIS is the kind of stuff you really need to work out, even if it's just roughly. Zak and molon have it down.

Assuming, of course, that you've worked out all your zeros.

If you don't know how much to lead a moving target, the 1/1000th of a MOA that you've saved by spending money on a rifle that shoots better than you can is wasted time.

You SHOULD know your zeros for ranges other than what you've mechanically zero'd for (what's your "hold-over" for 100, 200, etc), AND you should have some grasp of lead distances for at least walking and running (unless they're running away, they can't run fast enough to have to lead them, lol).
Link Posted: 2/14/2006 5:36:54 PM EDT
I'm from Louisiana, which competes with Arkansas for illiteracy, lack of math skills, and short attention span (AADD). We just open up on full auto and "walk" the entire 30-rd magazine into the target. Some will hit 'em. Oops, did he mention something like one shot, one kill? Better call up that ole squirrel shooter from West Virginia.
Link Posted: 2/15/2006 6:16:51 AM EDT
I was being facetious. I shoot a good bit, but not as much LR as I would like. I'll probably be going through our DDM course soon. If you guys are interested in this type of stuff, you may want to invest in a program called "Shooter ready." It's probably one of the best basic sniper math and windcall tutors I've seen.
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