SFP scope question

Joined
Aug 2, 2021
Messages
607
I understand that the reticle in a second focal plane scope is only accurate at its highest magnification, but I need help understanding how it affects dialing. For example I have a 5-20 power scope that I zeroed at 100 yards at 20 power. If I was on 12 power and wanted to shoot a target at 400 yards would the amount I dial be the same as at 20 power?
 
Joined
Nov 7, 2012
Messages
7,411
Location
S. UTAH
I understand that the reticle in a second focal plane scope is only accurate at its highest magnification, but I need help understanding how it affects dialing. For example I have a 5-20 power scope that I zeroed at 100 yards at 20 power. If I was on 12 power and wanted to shoot a target at 400 yards would the amount I dial be the same as at 20 power?

Yes. It only matters if you are using the hash marks to hold off your target.
 
Joined
Aug 10, 2015
Messages
2,249
If you have a 5-20x, there's a chance that your scope subtensions are not valid at the highest power. I have seen some vortex scopes that specified the subtensions were correct at something like 18x for a 5-20x. FYI. That's just an example, not necessarily verbatim from the manual.
 
Joined
Dec 30, 2014
Messages
8,185
Ballistic calculator makes that a non-issue.

How? IMO it's always an issue. One can you can find solutions for but also one that solutions wouldn't be necessary with FFP. You can dial windage i guess but it's not often the wind stays constant.

In all fairness, someone who doesn't know that zero shouldn't change with a magnification change has a ways to go before all these details matter.
 
Joined
Oct 8, 2019
Messages
2,956
How? IMO it's always an issue. One can you can find solutions for but also one that solutions wouldn't be necessary with FFP. You can dial windage i guess but it's not often the wind stays constant.
Should be close to the same process as with FFP.

This has worked for me except when I mangle the wind call. If there’s a better way (excluding going with FFP), then please let me know so I can adjust.

Using StrelokPro for demonstration purposes.

Measure (or guess) the wind. Open your ballistics app and go to your rifle’s profile. Enter the wind speed. Recalculate and you should see the required wind. Go to your reticle and adjust your magnification to match your scope. See which hash mark to use; yellow dot on target. You can adjust elevation as well to make it easier to see.

First you do need windage hash marks or you are going to have to dial. True for SFP and FFP. Second, may not be 100% lined up due to fraction of MOA (as example). Should be true for FFP as well.

There may be times you may be better served going up or down a value to get better alignment (ex: if the MOA splits the hash marks). Should not be an issue as you know where the animal is located.

Keeping things simple. 10 mph @ 90*.
1F2D6F88-5A89-40AD-B4A2-2F1B5251CEE0.jpeg

Example of 15x scope set to 9.5x (match scope).
84C03452-F8AE-4888-987B-EDD80BB4D211.jpeg

Example of 15x scope set to 6x (match the scope).
5E68C189-C8CC-463E-A970-BC8345E1D4AB.jpeg


I’ll do something similar for elevation if I’m in a spot for awhile. I’ll range around me and then look to see what the hash marks line up to for distance at a set magnification. This allows me to hold over and shoot if I need to take a quick shot. I know if it’s beyond then I’ll have to dial.
 
Joined
Dec 30, 2014
Messages
8,185
Should be close to the same process as with FFP.

This has worked for me except when I mangle the wind call. If there’s a better way (excluding going with FFP), then please let me know so I can adjust.

Using StrelokPro for demonstration purposes.

Measure (or guess) the wind. Open your ballistics app and go to your rifle’s profile. Enter the wind speed. Recalculate and you should see the required wind. Go to your reticle and adjust your magnification to match your scope. See which hash mark to use; yellow dot on target. You can adjust elevation as well to make it easier to see.

First you do need windage hash marks or you are going to have to dial. True for SFP and FFP. Second, may not be 100% lined up due to fraction of MOA (as example). Should be true for FFP as well.

There may be times you may be better served going up or down a value to get better alignment (ex: if the MOA splits the hash marks). Should not be an issue as you know where the animal is located.

Keeping things simple. 10 mph @ 90*.
View attachment 340335

Example of 15x scope set to 9.5x (match scope).
View attachment 340337

Example of 15x scope set to 6x (match the scope).
View attachment 340338


I’ll do something similar for elevation if I’m in a spot for awhile. I’ll range around me and then look to see what the hash marks line up to for distance at a set magnification. This allows me to hold over and shoot if I need to take a quick shot. I know if it’s beyond then I’ll have to dial.

I would not consider that to be solving the problem. It the example you gave, it’s still an unnecessary extra step to mess around with what mag your at in an app and then remember a hash that isn’t the angular measurement you actually need to hold.

Relying on an app with any time constraints (like hunting) is already a good way to miss an opportunity. At least it was for me the couple times I tried to get dope from a kestrel as bulls fed out of sight.
 

SDHNTR

WKR
Joined
Aug 30, 2012
Messages
6,210
This is the correct answer. The magnification ONLY changes the hash marks, not the actual zero. That’s personally why I’d rather by a good scope that I can dial, without a bdc type reticle.
This. Never understood why folks like all those busy and complex Nightforce type reticles AND dial. Unnecessary redundancy and cluttter.
 

SDHNTR

WKR
Joined
Aug 30, 2012
Messages
6,210
I would not consider that to be solving the problem. It the example you gave, it’s still an unnecessary extra step to mess around with what mag your at in an app and then remember a hash that isn’t the angular measurement you actually need to hold.

Relying on an app with any time constraints (like hunting) is already a good way to miss an opportunity. At least it was for me the couple times I tried to get dope from a kestrel as bulls fed out of sight.
This too. Time is often of the essence. I’ve seen excessive gadgetry cost opportunities far too many times.
 

davsco

WKR
Joined
Jan 30, 2018
Messages
738
Location
VA
sfp is good if a) you're going to be at max magnification or b) you are going to dial (elevation and windage). unless you're at max magnification, your elevation and windage hash marks will not be accurate. of course there is some math you can do to make it work, but prob not advised when that elk is finally in your scope.

the OP's question has already been answered, but, yes dialing is always accurate (well, if you have good turrets...) at any magnification whether ffp or sfp.

i recently bought a 3-15 sfp scope (from here) and i greatly prefer holding over dialing. but i figure i'll be at 15x if i'm doing anything over 200 yds (so the reticle will be accurate) and within 200 my drop is 2+/-" so i can hold right on at low magnification. so, safe either way.
 
Joined
Dec 30, 2014
Messages
8,185
This. Never understood why folks like all those busy and complex Nightforce type reticles AND dial. Unnecessary redundancy and cluttter.

I’ve never understood what is so complex about putting the crosshairs where you want to hit regardless of there being any additional subtensions. The crosshairs in the middle aren’t hard to find.

On the other hand, it’s hard to hold wind (like nearly everyone who understands this stuff and does this at a high level does) without useful subtensions on a reticle. How do you measure your corrections? Reticles make it easy.

It’s perfectly reasonable to dial when you have time and hold if you need to save a couple seconds. Say a deer offers a shot at 300 yards but body language indicates it won’t be there long. I know I need a mil of elevation @ 300 yards and I can put that mil hash on him and shoot quicker than I can dial and do the same and my point of aim will be more precise than any guess hold over or MPBR shot.

IMO if the only thing someone uses a basic mil reticle for is corrections and zeroing at the range, the usefulness still outweighs the non-existent clutter problems.
 
Last edited:
Joined
Oct 8, 2019
Messages
2,956
I would not consider that to be solving the problem. It the example you gave, it’s still an unnecessary extra step to mess around with what mag your at in an app and then remember a hash that isn’t the angular measurement you actually need to hold.

Relying on an app with any time constraints (like hunting) is already a good way to miss an opportunity. At least it was for me the couple times I tried to get dope from a kestrel as bulls fed out of sight.
The saying “a poor craftsman blames his tools” applies to hunting. It is up to each of us to figure out the best way to make a clean kill given our current tools and skill level.

You asked and I told you what I do. I also said that if there’s a better way to do it with SFP, then I’m all ears. What I do works at the range and the field when I do my part.

Lots of animals die each year, at various distances and crosswind speeds, with the much maligned SFP scopes that often are not at max magnification. Dumb luck can’t account for each of these kills.

Sometimes an animal will give you plenty of time. Sometimes an animal will literally give you 5-10 seconds. Sometimes the animal will just bolt. Unless I’m mistaken, animals don’t go “damn he’s running a FFP scope so I just need to stay here”. They are going to do what they want when they want despite what setup we are shooting.

If a hunter regularly has insufficient time to get a shot off, the hunter may be well served by practicing speed drills for the entire shooting process. This becomes more valuable when hunting solo. Working on their glassing and field craft may also benefit them as well as both can provide more time to get a shot off.

End of the day, people should do what works for them. At the same time, folks shouldn’t look down on others who do things differently.
 
Joined
Jul 6, 2018
Messages
493
I like FFP for accurate windage marks at any magnification but it’s not exactly rocket science to figure out the marks on an alternate magnification on a SFP scope (e.g. on a 16x scope at 8x the mark values are doubled).

It’s not the slickest way but neither is mentally figuring where the bars would cross for closer shot with an FFP scope because the crosshairs are basically invisible at low magnification. But plenty of people manage to be deadly with either.

It’s just like the endless threads debating the minutiae of bino harness design or whatever — in the end just pick one and really practice with it
 
Joined
Sep 15, 2020
Messages
623
In an SFP scope, magnification affects the relationship between the distances of points on the reticle to the center, but doesn't affect the positioning of the center of the reticle in the scope. Because of this, corrections made by dialing will be true at any mag, while corrections made by holding will follow the below formula:


(Value in Reticle) x (Subtended Power) / (Current Power) = (Value in Reticle at Current Power)

Example; For a 6-18x50 scope that is Subtended at 18x using a 1 Mil hold at 6 power:

1 Mil x 18/6 = 3 Mil

Example; For a 6-24x56 scope that is Subtended at 12x using a 1 Mil hold at 24 power:

1 x 12/24 = 0.5 Mil


Hope that helps.
 

ID_Matt

WKR
Joined
May 16, 2017
Messages
1,346
Location
Southern ID
This. Never understood why folks like all those busy and complex Nightforce type reticles AND dial. Unnecessary redundancy and cluttter.
A good reticle can be extremely useful if you know how to use it and spot impacts. Generally I will dial my first shot if I have time and then if I am off, measure the impact with my reticle and adjust accordingly. Without a good reticle you are just guessing on your holds after that.
 
Top