New Posts New Posts RSS Feed - Estimating Distance W/MIL DOT Fixed vs Variable
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

Check GunBroker.com for SWFA's No Reserve and No Minimum bid firearm auctions.

Estimating Distance W/MIL DOT Fixed vs Variable

 Post Reply Post Reply   Topic Search Topic Search  Topic Options Topic Options
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/03/2011 at 12:32
Ranger007 View Drop Down
Optics GrassHopper
Optics GrassHopper
Avatar

Joined: January/23/2011
Location: MA
Status: Offline
Points: 4
I am a novice shooter and tried to find the answer and so far no one can give a logical answer that makes any sense. So this you could say is a last resort and depending how this goes could be a first resort from here on out.
 
First let me explain some issues that have lead me to ask this question.
 
I am running a REM 700 SPS short action chamber in .308 WIN. with a SS 16x42 Fixed MIL DOT. Yes I know that the optic is a little much for the rifle but so far it does exactly what I want it to do.
 
My question is and please forgive me if a fudge the correct terms etc. If I am using the optic referenced above to estimate distance to the target how does a variable power scope affect range estimation? Meaning if I estimate my range to the target to be 150 yards in a X3 magnification and I then zoom in to the target on say 10 power the MIL DOT recticle does not change? Is that correct? If it is correct and the rectilce does not change how does one know what power to be at in order to estimate range estimation?
 
I am asking this question becuse the people at MIL DOT Master can not answer this. 
 
Any info/assistance would be greatly appreciated. 
 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/03/2011 at 12:49
SVT_Tactical View Drop Down
Optics Retard
Optics Retard
Avatar
Chief Sackscratch

Joined: December/17/2009
Location: NorthCackalacky
Status: Offline
Points: 28753
Variables with SFP will have a certain power in which the mildots are true, normally posted in an owners manual or somewhere.  However FFP scopes are true on all powers.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/03/2011 at 13:21
Urimaginaryfrnd View Drop Down
MODERATOR
MODERATOR
Avatar
Resident Redneck

Joined: June/20/2005
Location: Iowa
Status: Offline
Points: 13877
Most scopes use the highest power as the correct power to mil dot rangefind which makes sense  because that allows you to more accurately estimate tenths of a mil.  Some manufacturers use a specific power as the correct one to mil at like 12x which Bushnell seems to like.  Recently we have been seeing some first focal plane scopes which will mil rangefind at any power and as you zoom from low power to high power the reticle grows larger in appearance but the dots are always one mil apart.  The traditional style second focal plane scopes the reticle always appears to stay the same size.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/03/2011 at 13:44
Ranger007 View Drop Down
Optics GrassHopper
Optics GrassHopper
Avatar

Joined: January/23/2011
Location: MA
Status: Offline
Points: 4
Thank you very much Urimaginaryfrnd and  SVT_Tactical!!!!!!!!
I am tracking. Yippee
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/03/2011 at 15:37
jonoMT View Drop Down
Optics Master Extraordinaire
Optics Master Extraordinaire
Avatar

Joined: November/13/2008
Location: Montana
Status: Offline
Points: 4613
To expand on that, let's look at three examples: 1) Your 16x fixed-power scope, 2) a variable FFP scope and 3) a variable SFP scope. In all three cases, we'll range a target 12" in size @ ~150 yards.

  1. The fixed power scope is essentially like an FFP scope, just with one power. So the ranging equation is straightforward and always the same. 12" = ~.333 yards. Multiply that times 1000 and you'll get the distance it would be if the target spanned 1 mil. Now, say the target actually spanned 2.2 mils (Let's be realistic. It's hard to get a precise number looking through a reticle). Divide 333 by 2.2 and you get 151.36 yards.

  2. With the FFP scope, the equation is going to be exactly the same as with the fixed scope. The only difference is that when you change magnification, both the reticle and the target change size - together. With an FFP scope, the target will still span 2.2 mils whether @ 3X or 15X. So there is no additional math or having to ensure that you're on the scope's ranging power. You just have to be on a high-enough power to accurately measure.

  3. An SFP scope will also require no additional math either - but only at its ranging power. Consider a scope, such as a 2.5-10X with a ranging power @ 10X. Measure 2.2 mils across that 12" target @ 10X and the math is the same. However, what if you want to range @ 5X? You would look through the reticle and see that the target only spans 1.1 mils. If you divide 333 by 1.1 you will get 302.73 yards. So either you need to first multiply the mils by the ranging power divided by the current power, e.g. 1.1 x (10/5) before dividing. Or divide the results by the ranging power divided by the current power, e.g. 302.73/(10/5) = 151.36

    Take the scope down to 2.5X and your same target now subtends only .55 mils. You would either need to multiply that times 4  (using 10/2.5) or divide the resulting distance by 4 (606.45 /4) = 151.36.
So you can see that ranging with an SFP scope is most easily and best done on its ranging power. Or at worst, on half that power so you can just multiply or divide by 2, depending where you prefer to factor that in. For a scope that only goes up to 10X, SFP is not much of a limitation. Personally, I never range anything under 300 yards and for more than that, you really want 10X. For a scope with a ranging power of 22X, IMO SFP is a serious limitation. My preference for a scope that goes beyond 10X is definitely to go FFP. Aside from not worrying about being on a specific ranging power, you can also use the reticle to correct your point of aim at any power.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/04/2011 at 21:15
Ranger007 View Drop Down
Optics GrassHopper
Optics GrassHopper
Avatar

Joined: January/23/2011
Location: MA
Status: Offline
Points: 4
Excellent. I am tracking and I actualky understand it too. Thank you all very much greatly appreciated! Ho-Ah!!
 Post Reply Post Reply
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Similar Threads: "Estimating Distance W/MIL DOT Fixed vs Variable"
Subject Author Forum Replies Last Post
Mil-quad vs. Mil-dot onfinal Rifle Scopes 4
Variable Mil-Dots on a budget.... taylorsf Tactical Scopes 12 3/15/2006 6:16:57 PM
Variable Mil-Dot Scope Help??? Ironman Tactical Scopes 7 7/19/2007 1:13:43 PM
scope suggest 6X OR 8X fixed scope(mil dot) Rong1 Rifle Scopes 2
12x fixed power mil dot? Neato Rifle Scopes 2
Original S S Fixed -Mil Mil MilQuad Urimaginaryfrnd Tactical Scopes 14
Review of new SS10x42MQ (mil/mil fixed 10 power) dk-1 Member's Tests and Reviews 7
Mil Quad or Mil Dot ? bcraig Rifle Scopes 3
SWFA- MIL/MIL Higher X Variable USN_Sam1385 Rifle Scopes 16
variable versus fixed power jackofalltrades Rifle Scopes 9


This page was generated in 0.219 seconds.