Reticle Subtensions

Malazan

Malazan

New member
ugh...me no good with math
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Ok, let me try to ask this so folks will understand


Lets say, I have a 5-20x50 scope with an MOA reticle, graduated in 1 MOA increments for elevation.

Now, this is a 4x erector correct? So at 20x the MOA is 1, at 10x it is 2 MOA per mark, 6.5x it is 3 MOA, and at 5x it is 4 MOA per mark, correct?

How do you figure the other powers, i.e. 16x?

Do you take 20 and divide by 16... 20/16= 1.25, so at 16x, each mark is 1.25 MOA?

Help
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I am not sure I understand your question for sure.

But maybe this will help you.

Scopes with the reticle in the 1st focal plane (usually European mfg.) the size or thickness of the reticle stays in proportion to the target as you change magnification (appears to grow with magnification). Therefore the subtension does not really change.

Scopes with reticle in the 2nd focal plane (USA mfg., not all though.) are installed behind the magnification lense, thus the reticle will appear the same size throughout the magnification range. This translates into the reticle subtension being accurate at only one magnification setting (usually the highest).

Perhaps someone more knowledgeable and knowing which brand of scope you have can help you better.
 
No I understand the hole FFP/SFP with regards to the reticle size, and I understand that the subtension measurements in the FFP stay the same through all the magnification ranges.

I want to know how to figure the reticle subtension values at different magnification settings.
 
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I'm definitley into this kinda' stuff-but i'm far from any kinda' calculus. All reticles and turrets require is simple algebra (division and multiplication). Wouldn't know a calculus if it hit me in the head.

M-- the question you're asking about is what the Nikon Spot-On ballistics program uses when they change magnification (and consequently subtension). Leupold uses it in their ballisitic reticles and Exbal uses it too.

The system is inversely proportional (assuming the power ring is cald. properly--some are close, some not so close)--as magnification DECREASES reticle subtension INCREASES.

So yes your subtensions are correct except for the 12x mag. which would be 20/12= 1.67 MOA

Ineteresting story about mag and subtension changes. I was hunting wih a buddies kid one day when i asked to take a look at the Marlin 22 he was carrying. It had a Simmons 3-9x rifle scope ontop with plex reticle. The plex post tips appeared to subtend ~6 MOA at 9x from center X. I told this kid that if he cranked it down to 3x it oughtta' be very close to 18 MOA, and might get him out to about 300 or so, so we decided to test it on a couple prairie dogs. I lasered a couple at 290-something. So this kid sets up on a PD mound and fires a shot. The bullet impacted several inches below the dog, so the kid compensates and shoots again this time nailing the dog and it rolled off the back of the mound. It runs back up and hesitates just a bit on top the mound when the kid shoots and nails him again killing it. His buddy comes out of the hole barking at his dead brother, and a couple shots later this kid nails it too. I couldn't believe it when i walked up to the mound, but sure enuf there they both were. Amazing what can be accomplisehd sometimes using a little math in the field.
 
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