I typed this one or 2 year's ago on PLRH; I'm too idle to type it again [img]/ubbthreads/images/graemlins/smile.gif[/img] looks like noone read it anyway!

<font color="blue"> The 'base line' [or 'corrected horizontal range' or 'magic physical-law defying range'] method, although used by many is actually the least accurate way of using your cos measurement...because it has absolutely nothing to do with the ballistics of what's going on in inclined fire!

Far more accurate is to multiply the comeup you would have applied for your laser distance by the cos of the angle.

This does reflect what is going on ballistically ...the bullet has the same TOF to a given target regardless of angle of fire...it therefore drops the same amount regardless of angle of fire (it doesn't magically drop less!)

...what changes is your perspective to that drop (and therefore the apparent shape of the trajectory).

Hold a pencil vertically in your hand at arms length (with your arm horizontal); lets say the pencil length represents your bullet drop at 1 arms length.

Now drop your arm to 45deg, but keep the pencil vertical.

The pencil appears shorter, even though it has remained the same length

....ie the drop has remained the same, but less drop is apparent because of your perspective.

How long does it appear to be? multiply it's actual length by the cos of 45deg...just the same as multiplying your laser range comeup by the cos of the angle!

You'll see that Ward at ACI has recently amended his instructions for the ACI to reflect this.

Here's a link to a link on the ACI site where all this is explained by one of the Sierra Infinity software designers:

http://www.snipertools.com/article4.htm
Only read this bit if you're a ballistics nerd: The software engineer concludes that a set of rather complicated calculations based on actual bullet drop (rather than simply comeups) are somehow yet more accurate again (this is the method he uses in the Sierra program)...he tests his theory by comparing the results of this type of calculation against his Sierra outputs...they are close to each other so he concludes greater accuracy...what he fails to point out / realise is that both the calculation method and his software method are the same...of course they'll be close!! ...nothing proved!

...unless a ballistic prog goes into a full vector analysis of how gravitational acceleration is affecting bullet velocity throughout its time of flight (and therefore calculating the minute changes to TOF at varying angles of projection)(ie 'straight up' it will directly slow the bullet, 'straight down will speed it)the only greater accuracy from a basic ballistic prog comes from the fact that 'comeups' represent data that has been rounded-of to the nearest click value, if you use that and then round-off the result..the answer will be slightly less accurate than precise raw data that has only been rounded off once.

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...and as a common-sense check:

Artillerymen receive target locations as grid references.

Grid references alone provide no angle of sight data (ie should the target happen to be on top of a hill or in a valley); and so Gunners are presented immediately with what some riflemen are calling 'true horizontal range'.

But Gunners, if working manually, will use this distance, (plus some trig based on the calculated angle of sight between their location and the target's) to work out the 'slant range' to the target (and then do some other mumbo jumbo too)

....the point being; true long range Jedi [img]/ubbthreads/images/graemlins/smile.gif[/img] do (and have done since WW1!) the exact opposite of what the 'corrected horizontal range' riflemen suggest.