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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/25/2010 at 14:09
EPDP99 View Drop Down
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After doing research and trying to rack my brain to understand them...for the ranging and holdover. I see that most scopes are set to 10x when using the mil dots for ranging. does this ring true for hold over as well since the distance will get larger when more power is used. It seems like it would make sense to me. but for using long shhots and the additional power can a mil dot scope be used for holdover and if so how. I see at 100yrds 1 mil=3.6 inches and so on. at 200 the first dot=7.2 inches and so on. Basically can they be used on any power but the setting for the scope(ie:10x). or only that power like the BDC reticle needs to be on max power?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/25/2010 at 14:21
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This why first focal plane scopes have been developed! If the scope is a second focal plane then the reticle is only good at the magnification set by the manufacturer. Whether for ranging, or hold-over. If it is a first focal plane scope, the reticle is correct at any magnification. 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/25/2010 at 20:48
Dale Clifford View Drop Down
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partially--- with sfp scopes the point of aim lowers with a decrease in power, which when corrected by recentering the cross hair raises the poi. sfp do not need to be at the highest power to use (a common misconception) but the shooter needs to know the correction factor which is not linear, whereas the ranging factor or fraction will always be linear or proportional. Zeiss , swaro and nightforce provide online computer services that will give the correct power setting for the load you are using, if its something you need, and its rarely at the highest setting. Another example is my 8x32 nightforce with the np1rr, which not only ranges at 22 but the drops are set at 22 rather than the highest power of 32. Even at that the correction factor is used to set the hash marks at some even interval such as 100, 200 etc yds. If you can think of the correction in terms of moa drop at the target, it does away with the mental conversion, (mental gymnastics) most people go through correcting back to a meaningful yardarge, which the moa drop approach has already built in by definition, because the yardage interval would be something odd like 132 yds, instead of say 100 yds.  
While ffp apparently does away with this, seeming voodoo, it introduces other problems,
they also need to be used at the highest power to range, as this gives the most accurate values, so they gain little in comparison on sfp.
the increases size of the reticle makes bi-secting the target or shooting a some precise point of the target almost impossible which is made worse the higher the erector ratio becomes.
most ffp with any mag. range have severe tunneling problems on the lower ends.


Edited by Dale Clifford - April/25/2010 at 20:49
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/26/2010 at 06:16
Jon A View Drop Down
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Originally posted by EPDP99 EPDP99 wrote:

Basically can they be used on any power but the setting for the scope(ie:10x). or only that power like the BDC reticle needs to be on max power?

Correct.  For a mildot scope in the SFP the reticle will only correctly subtend in mils at one specific power.  For example, if your particular scope is calibrated for 10X but it's a 14X scope, the Mil marks will be somewhere around 3.6 X 10/14 = 2.57" per hundred yards when set to 14X.   I don't suggest having too much faith in the power ring on the scope though, so if you want to use the scope in that manor I recommend measuring the reticle subtensions at that power using a collimator, or barber pole/yardstick set at 100 yds, etc. 

Once you've verified that you can figure out what your holdovers on the reticle will be with the scope set to the power you want to use.  Of course, using a FFP scope means you can avoid all this nonsense and always know 1 mil on your reticle is always 1 actual mil no matter what.      Excellent

Originally posted by Dale Clifford Dale Clifford wrote:

most ffp with any mag. range have severe tunneling problems on the lower ends.

Most things mentioned have been discussed in depth here, but I've been seeing this last part pop up numerous places lately.  It simply isn't true.  Scopes can have tunneling problems or not, it has to do with many aspects of the optical design but whether it's a FFP or SFP has nothing to do with it.  Some of the least tunnel effect scopes on the market are FFP.  The Hensoldts have already become notorious for "the body of the scope disappearing" since becoming available here recently.  One of the more recent examples I've dealt with lately is the 1-4X24 SS which is FFP.  Here's a pic of it on 1X:



And here's a pic of the excellent and highly respected Nightforce 1-4X24 which is a SFP:



Hopefully that will put to rest the notion that FFP and tunnel effect go hand in hand.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/26/2010 at 08:20
Dale Clifford View Drop Down
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also as stated the tunnel effect depends on the ratio of the erector magnification, a 1x 4 wouldn't be as noticable. The ffp scopes that I have with this tunneling effect are the following
IOR 3x18
Zeiss 3x10
S&B 5x25
USO 3.2x17
Haven't tried all of them, maybe the razor will have some of this corrected.
Hope this puts to rest that ffp is always the best way to go.


Edited by Dale Clifford - April/26/2010 at 08:22
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/26/2010 at 13:11
Jon A View Drop Down
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It's coincidental the ones you have looked at with tunnel were also FFP.  Every IOR I've ever seen has it in some amount, both FFP and SFP (by far the worst was a 4:1 2.5-10 SFP).  My 4:1 S&B had it, but my Premier 5:1 has not a hint of it.

The point is if the optical design of the scope gives it a tunnel effect, it'll have one, if not it won't.  It has nothing to do with where they put the reticle.  They are unrelated. 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/26/2010 at 14:51
Dale Clifford View Drop Down
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circular reasoning, it exists regardless of the cause.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/26/2010 at 19:13
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I saw some slightly noticeable tunneling effect in the SS 3-9 (FFP) scope below 4X but have not noticed any in my Premier either (also FFP). My NF 2.5-10X32 (SFP) has a slight amount below 3X. In no case did I feel like it was enough to be distracting.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/26/2010 at 19:38
Jon A View Drop Down
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Originally posted by Dale Clifford Dale Clifford wrote:

circular reasoning, it exists regardless of the cause.

There's nothing circular about it.  Your post indicated FFP was the cause or was somehow related to scopes having a tunneling effect.  That's simply not the case.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/26/2010 at 20:23
Dale Clifford View Drop Down
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whats the case Jon, if not the design, some ffp may improve the design or minimize it, it doesn't exclude other causes of tunneling it simply includes ffp in the set group of tunneling image scopes, coincidence, correlation, doesn't change the observation.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/26/2010 at 20:52
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Nevermind.  
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/26/2010 at 21:15
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I'd highly recommend a scope that is FFP and that has both a mil reticle and mil turrets. Because the ratio of mils to target size is always the same regardless of magnification, using an FFP scope means you can range at any power. It also means that you can either use reticle or the turrets (if they are also in mils) to make  a correction for a follow-up shot. (In an SFP scope, the ratio of mils to target size to the adjustments made by the turrets only works at its ranging power, which is usually the highest power).

Some moderately priced FFP scopes to consider are the $599 SS 3-9 or the upcoming $850 Vortex PST 4-16. From there, your next price band is with the IORs ($1040-$1500) and then you enter the $2000+ market (Vortex Razor HD, NF F1, Premier, USO, S&B and Hensoldt).
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: April/26/2010 at 21:24
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http://www.jbmballistics.com/cgi-bin/jbmtraj_drift-5.0.cgi  make a balistics chart for your rifle caliber bullet selection and at the bottom where you can select to have the trajectory shown in 1/4 moa  etc select mil  and it will give drop correction in mil then you can use a mil dot for known hold over.   The easiest stuff to think through is a mil based  first focal plane scope with a mil based reticle like the 3-9 Super Sniper and there are some others Vortex is making one, Nightforce makes a nice one etc.
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