# Ballistic/Ranging reticle rangefinding

Discussion in 'Long Range Scopes and Other Optics' started by sscoyote, Jan 25, 2005.

1. ### sscoyoteWell-Known Member

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Thought i'd copy this over from the Long-Range thread on Specialty Pistols:

Been looking a lot at the TDS Tri-Factor System lately in the Swarovski/Kahles scopes. The system he uses for ranging can be modified to work for any ballistic reticle, such as the LR handgun Ball. Plex. Here's how it would work:

Ball. Plex reticle subtensions for 3-12=

1.4", 4.1, 6.8, 10.1

Now using the entire 10.1" gap for a 24" back to brisket cow elk, then the modified mil-ranging formula is:

24" x 100/10.1/# stadia units in tenths of a unit that the 24" target brackets, or:

.9 SU = 265
.8 SU = 300
.7 SU = 340
.6 SU = 400
.5 SU = 475
.4 SU = 600

Now each stadia line in the reticle can be used as a reference to have a more accurate system, helping a lot with interpolation, and to calculate what part of the gap each stadia is, just divide the full gap subtension into each stadia subtension as follows:

1.4/10.1= .1 of the total 10.1" gap, and

4.1/10.1= .4

6.8/10.1= .7

Now u have 2 more ranging references with the 2nd and 3rd stadia to help with interpolation (the 1st stadia-- .1 calculates to 2376 yds.-- a little too far for my guns, i think). This system has been proven by the originator of the TDS reticle to work quite well for ranging purposes for larger game (deer and bigger).

2. ### Ian MWell-Known Member

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SS
If you ever wanted to discuss this data with TD there is an 800 number that will get you to him. He is an amazing person - discussing ballistics with TD is an experience - in fact he has done so much in his life that any discussion with him is a memorable moment. I doubt that Hollywood could create the special effects for some of his adventures - and he did them. He came up with the math for the TDS while recuperating in a military hospital after surviving a crash - not sure which crash tho. His squadron in Viet Nam specialized in attacking SAM sites. Amazing individual, I am fortunate to know him.

3. ### sscoyoteWell-Known Member

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Ian-- just talked to him today for the 1st time-- interesting guy, for sure. I read the writeup that Jacob Gottfredson did on the guy in Tactical Shooter mag.-- MAN what a fascinating guy, and life, he's had-- 1 in a million for sure-- heck maybe more.

U know it's interesting-- this reticle ranging stuff. Of all the guys i've talked to about it he and Gerald Perrry probably know as much about it as any i know.

4. ### Ian MWell-Known Member

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I spent most of a week with TD and another Viet Nam pilot vet, just sat and listened to the stories and grinned - those fellows had balls. Too bad that they do not get the recognition that they deserve - they were incredible warriors but just doing their jobs at the time. Hope you meet up with TD sometime, he is usually at the SHOT show, Swarovski booth area. There is only one TD Smith.