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Shockershot87
06-05-2015, 16:10
Currently downrange, trying to figure out a question posed to me by a Allied soldier when discussing Mortar techniques.

Why do we sight in mortars with a deflection of 3200 mils instead of just using 0000/6400? Is there a actual reason? Or was 3200 just picked and that's how the sight just is?

Thank you

SFOC0173
06-05-2015, 16:26
http://www.globalsecurity.org/military/library/policy/army/fm/6-50/Ch4.htm

SF_BHT
06-05-2015, 19:44
http://www.globalsecurity.org/military/library/policy/army/fm/6-50/Ch4.htm

Why not explain it instead of giving a link to a whole manual.

Well go to this spot 4-15. PRINCIPLES OF LAYING.

Basically you can lay out the guns (artillery or mortar's) with your stakes forward or to the rear. By using 3200 you stop a sight blockage. Depending on your firing position you set out your stakes forward or rear. The aiming circle is used to set everything in alignment and verify to make sure your guns are all firing in the same direction. You can lay our your guns in many patterns and the circle is there to keep them all in sync with each other. As you traverse your guns you want to not have a sight blockage so 3200 is the best azimuth to get the most out of your traverse and not have to re-lay the guns.

I could draw a lot of diagrams but the linked manual has a few. Let me know if you need more info. shoot I guess IMPOC paid off....

CSB
06-05-2015, 19:46
It minimizes errors when making shifts in traverse (left and right).

The gunner / FDC doesn't have to "make the jump" at zero.

3300 mils minus 150 miles equals 3150 mils.

3125 mils plus 250 mils equals 3375 mils.

But if you used zero mils as your index line, then:

100 mils minus 150 mils equals 6350 mils.

and

6275 mils plus 325 mils equals 200 mils.

Shockershot87
06-06-2015, 04:24
It minimizes errors when making shifts in traverse (left and right).

The gunner / FDC doesn't have to "make the jump" at zero.

3300 mils minus 150 miles equals 3150 mils.

3125 mils plus 250 mils equals 3375 mils.

But if you used zero mils as your index line, then:

100 mils minus 150 mils equals 6350 mils.

and

6275 mils plus 325 mils equals 200 mils.

Thank you. That makes the most sense.
SF_BHT, I understand what you're saying and it wasn't totally my question. I know that's also why we lay the guns in and place stakes with 2800 referred so that you have a greater degree of deflection changes before hitting sight block.

Thank you all, for taking the time to answer this for me.

geardo211
06-09-2015, 12:30
When using the plotting board, LHMBC, or MFCS you typically also lay out 0700 poles to cover the sight block deflections. The gunner informs the FDC that he has a sight block and shifts to them while the fdc recalculates the mission for said deflection. In the newest software updates or on the M16/M19 theoretically any deflection could be your refer deflection, but we usually subscribe to KISS. The mortar pit at FOB Sweeney would be a good example where non-standard refer deflections were necessary, if anyone has been around Zabul province.

Shockershot87
06-10-2015, 06:06
Geardo,

Thanks for the reply. I'm spun up on sight block issues and why we typically will actually lay the gun in on 2800 so that it gives you 400 extra mills to play with before sight block. It was why the sight, when placed on the mortar, is indexed on 3200 instead of 6400. I'm working with some allied forces and they set the gun up on 6400 (never minding alt aiming stakes and sight block). They are also using our M67 sight.

CSB
06-10-2015, 11:20
If you are going to "dial in" a deflection for all tubes and drop rounds, using the 0-6400 index probably wouldn't make much difference.

Most of the time, the tubes are firing in parallel, hopefully each tube is spaced one bursting radius apart, and the rounds generate an area impact zone of interlocking splinters.

But if you want to be able to quickly converge your sheaf and drop all rounds onto a point target, the ability for each outlying mortar to make a quick "left-right" adjustment from the deflection used by the adjusting (base) tube -- by adding or subtracting an odd number of mils -- favors the 3200 reference line to avoid the "jump over zero" problem.