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Fallacy in Ballistic Reticles??

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/19/2008 at 04:39
sscoyote View Drop Down
Optics Journeyman
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This is the only place i can think of for posting this question since there are some guys here that understand angular geometry very well.
 
I think there may be a  fallacy in the application of ballistic reticles for long-range shooting, but i'm not sure.
 
OK, suppose u have a ballistic plex reticle and u know that the 3rd stadia is 400 yds. and the 4th stadia is 500 yds. Now a 450 yd. shot would be referenced right around the 1/2 way point, but i don't think the 425 and 475 yd. shots would be at the 1/4th and 3/4ths reference points. If angular geometry is right then shouldn't these ydgs. and others be skewed somewhat from the linear reference?
 
I'm asking this because i know that when used for rangefinding purposes the system is not linear. For example when using a rangefinding reticle that has stadia points at 2 inch per hundred yd.  intervals and you're ranging a 10" tgt., if it fits perfectly between 2 2 IPHY stadia points then it's 10 x 100/ 2 / 1.0 = 500 yds. away. If it fits 1/2 the subtension it's 10x100/2/.5=1000 yds. away, but if it's 3/4ths the subtension it's 1000/2/.75=667 yds. away so it's not linear.
 
...so isn't the reference for downrange zeroing not linear also??
 
This is a hard concept to explain but i hope somebody can read my garble well enuf to understand what i'm trying to say.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/19/2008 at 08:23
Dale Clifford View Drop Down
Optics Jedi Knight
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two types of ballistic reticles, one is evenly spaced (usually called loosly a milling system) in moa or mils, and a progressive type. can't think of any ffp progressive reticles although swaro may have some in the ph series. am assuming you are talking about the progressive sfp types which are really popular right now.

mentally seperate what the reticle is doing in angular geometry and what the load is doing because of gravity. milling or evenly severated reticles do this, progressive types integrate the mental , and combine the angular with the log drop on the ballistic curve pecular to that load. that is why the ranging properties of sfp are usually done on the highest power, although done any other power it is just a multiple of the highest. --- as long as the same stadia distance is used. moa sfp reticles such as nf, are (for me) easily done on sight and mil must be translated unless the turret is in mils.

the actual point impact is impossible sense no gun is capable of this type of accuracy, but usually a cone of fire. say 8 inchs is established-- at any given distance there will be a 4 inch window on top and 4 on bottom. from the theortical exact poi. if view along the horizontal axis it looks like an ellipsoid in front of the poi and behind it-- the as the bullet drops thru these areas.
 
now addressing your pts. no the 450 will not be exactly in the center, and the 425 and 475 will not be in direct proportion either-- but it doesn't its not a fallacy in the system. The best way to see this is to go to the zeiss web site and play with their z plex calculator. the swaro site has one similar and they are both uses of exbal that will show you the "hit" range before and after the actual value they calculate for that stadia. the zeiss site will ask you if you want optimization which is the value that usually gives whole numbers for the stadia wires, ( but usually has some dumb value like 8.54) and the swaro will show yardarges before and after.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/19/2008 at 08:31
Dale Clifford View Drop Down
Optics Jedi Knight
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the swaro uses a "group" value which is similar to leos BAS system in that it groups a bunch of ballistic curves together based on their trajectory similarites, and disregards caliber, velocity etc.

one can use the different progressive stadia distances for ranging, and even get whole yardage values by recalculating what power  the variable needs to be set on. this is really getting into it and takes some practice, as one is using the scope to "curve fit".
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: May/19/2008 at 16:12
sscoyote View Drop Down
Optics Journeyman
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Thks. Dale, i appreciate it!
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