How many of you understand a scopes "subtend"

DallanC · Site Admin Joined: Jan 18, 2005 Posts: 3572 Location: Utah

How many of you understand a scopes "subtend"? I know there are alot of guys here who do (huntingnut has more knowledgable people) but it seems there are an awfully lot of people who dont have a clue what it is and how it can be used to not only estimate ranges, but wind, leads, holdover etc etc.

I'm thinking about writing a comprehensive guide one of these days on it.

-DallanC

Dimitri · Super Member Joined: Nov 25, 2005 Posts: 5946

DO IT!

I've got no idea how to do it execpt that if you bracket a known size at a known distance at a certian maginfication you can "guesstamate" Razz

Help!

Dimitri

roklok

My Leupold Vari-X 3 3.5-10 on my .243 has two sets of digits marked on power ring,one of course is power the other is the estimated distance to the target by bracketing a 16 inch target between the crosshairs and the thicker point of the duplex reticle. On my .35 Whelen with 2-7 leupold I use the lower point of the duplex reticle as my 350 yard aiming point at 7 power.0-250 yards I aim using crosshairs,300 I aim midway between crosshairs and point,350 use the point,and 400 put point on the top of back.I have never had the opportunity to fire at an animal at this distance(big game) but have practiced this a good deal and have turned in some pretty respectable groups at 400 yards with my whelen and 7 power scope. I just called Leupold last week to see if their custom shop could install their long range duplex reticle or their new ballistically matched reticle in my scope but was dismayed to learn that they can only do that to their new VX series. So I guess I will continue using this system.

roklok

Its too bad that scope manufactures dont give the MOA of the reticle from center to thick portion at highest power. I know its easy to figure this out if using a 1 inch grid target at 100 yards but I dont normally keep such targets on hand,preferring to shoot at a simple 1 inch square black sticker on a sheet of white paper.

Coyote_Hunter_

I've been using Duplex reticles as rangefinders for quite a few years. These days I use a laser for accuracy but often use the reticle for fun.

Gil Martin

It depends. I think this would be a good topic to cover. Around here, really long shots are rare, except for groundhogs and perhaps deer. We tend to sight in a bit high at 100 yards and work with a point-blank hold. All the best...
Gil

sniper

DallanC wrote:

How many of you understand a scopes "subtend"?
-DallanC

If my understanding is correct, it is simply a big word to describe how much the scope reticle will cover at distances.

If the crosshair intersection will cover a 1 in. object at 100 yds, it is a 1" subtension. (Did I spell that correctly?)

Or could it also be used also for the thick/thin portions of the duplex reticle, too? Where the reticle goes from wide to skinny on either side of the intersection could be said to subtend 12" at 100 yds, I think, but that varies by manufacturer. It could be used as an approximate rangefinder.

If your crosshairs completely cover an object, it's generally too far/small to shoot at with reasonable expectation of success. Just my $.02

Spacedone · Member Joined: Nov 04, 2005 Posts: 266 Location: missouri

ok lets see if i understand this properly.

i look at the target and see the crosshairs and guesstimate the size of the target then guess my small recticle part is 18 inches at 100 yards and im at 300 yards so i carry the 2 and divide by 27 then add 9 and find the square root of 105 then subtract 33 and miss my target by the angle of a large lighthouse.

roklok

Leupolds standard duplex in their 3.5-10 has about a 2.66 MOA thin portion from intersection to thick point at 10 power.But of course as stated this varies by brand and also by magnification.

sniper

Spacedone wrote:

ok lets see if i understand this properly.

i look at the target and see the crosshairs and guesstimate the size of the target then guess my small recticle part is 18 inches at 100 yards and im at 300 yards so i carry the 2 and divide by 27 then add 9 and find the square root of 105 then subtract 33 and miss my target by the angle of a large lighthouse.

By George, I think you've got it! Very Happy

If you can see it without the crosshairs covering it, SHOOT! Then compensate, then shoot again.....Then... Shooting

Most manufacturers list the reticle statistics, including what we are talking about on the info sheet that comes with the scopes. You know, the one with the instructions we either throw away or put in the scope box and never see again? Now... where DID I put that scope box? Wink

Dawgdad

I have known that and used it on some scopes, but have found that I never reallly had time to check the magnification on my variable scopes when the shot presented. I usually range the terrain before the game shows up and set my maximum PBZ by a tree or a bush and do not shoot beyond that. (Of course that is all about to change if you read my thread in relaoding section)

My illuminated mildots are pretty slick for low light range guestimating with a Mildot master in my cargo pocket.

Flint54

I think that it would be a "Great" article. I have been doing some work with several of my scopes to find just the thing that you are talking about. It seems that no two are the same unless they are identical mfg & size. If you would like some input for the article krop me a PM. All the best. Cool