B.D.C. reticles and 1st and 2nd focal plane

[tribb]

As stated in the post I would like to know what happens to your multiple aim points when changing the power . Example: Suppose you sighted in the center cross wire at 100 yds at 10 power the other 3 aim points just happened to fall sighted in at 175, 250, & 325. You did this exact same thing with 2 different scopes both 4-20 power one first & one second focal plane. What happens when the power is changed to say 20 power? Forget about the cross hair being hard to see at low power that's not part of my question here! Will all non center aim points be off the original distances sighted for in : both scopes? only one scope? Or both scopes? If one scope remains sighted correctly at all aim point distances which will it be? I've never used a first focal scope before and know zero about how they function and i like the bdc type reticles! Or at the very least 2 aim points with the duplex type reticle thanks Tribb

 

[Ckleeves]

The FFP is going to be accurate across all powers, the SFP will not if I understand your question correctly. The reticle appears to grow and shrink in a FFP but it's staying the same size. In a SFP the reticle is only accurate at a specific power, whether your measure in mils or moa or using a BDC type system like your talking about.

So only one scope would remain correctly sighted in at all aim point distances, the FFP. I don't believe anybody makes a BDC type reticle in FFP, and for good reason it's much better to just shoot in mil or moa and with FFP you can either dial or hold off the reticle at any power.

 

[Laelkhunter]

Most SFP scopes with BDC reticle have to be at a specific power for the crosshair to be accurate. My Swarovski Z5 is SFP, and it has to be at 18X for the BDC to be accurate. Swaro has an Online Ballistic Calculator that tells you where each crosswire will put the bullet. This is useful only after you enter all of the load (cartridge) info, including BC of bullet, velocity, altitude, etc. On my Zeiss scope, basically similar, but it would tell you what power to place your scope on to hit the target at a specific range (IIRC).

 

[Tiny Tim]

SFP POI will change drastically with power changes. The 2.5-10 BDC on my AR is spot on at 200 yards at 10x, at 2.5x, this same dot is on at something like 490 yards.

For SFP, you would need to know the actual MOA/MIL values of the dots, then do the math at various powers. I have just learned that for me, actual MOA/MIL reticles are more beneficial for me.

 

[LDHunter]

I only use Second Focal Plane scopes because I zero my scopes at 200 yards and know the drop at 300yds and beyond that I only use a laser range finder and turn the dials. I know that there are specific applications where only a First Focal Plane scope is useful but for hunting I've never understood the whole need for FFP.

I get the whole chest size thing but to me that's pretty inaccurate and I'm not about "good enough" in ranging game. I want to know precisely how far game is from me if it's far enough that bullet drop can become an issue.

I owned a FFP NX8 4-32 scope and found it useless at low power because the reticle nearly disappeared and I couldn't imagine it working for me in a low light situation or one where a quick up close shot would be needed but I'm primarily a hunter and will never compete.

 

[med358-boise]

To put a finer point on this, neither scope loses accuracy but the correct zero yardages change on a second focal plane scope for the stadia marks or dots but not for the main crosshair.

Most scope companies, such as Leupold, Bushnell, and Sightron will provide you the relevant MOA subtension values for some or all of the power settings. However, the relationship for the change in the MOA subtension value is constant and works in an inverse manner; i.e., as the power setting goes down, the MOA value goes up. For example if, the scope is a 4-12 with a stadia mark every 2 MOA when set at 12 power; then those 2 MOA stadia marks become 3 MOA at 8 power and 6 MOA marks at 4 power because 12 is 1.5 greater than 8 and 3 times greater than 4. So the formula is divide high power setting by the low power setting and use that numeric value to multiply the "baseline MOA" value.

 

[Coach Jay]

In my experience, a sfp scope will have a white dot on a specific power that the manufacturer suggests is the closest in correlation. However, it is only a standard measurement that gets close unless it is for a specific caliber.

 

[AZShooter]

As already stated Second focal plane stadia spacing changes with magnification.

I remember having a conversation with the late Dave Miller of Dave Miller Co custom rifles. He used a Leupold scope which had stadia. Max power was 20X. He had the stadia come ups figured out for that power. He also found true 10X and had the spacing of stadia, which would be exactly twice the amount, figured out as well. That way he could still find an animal in the scope in low light with the 10X.

 

[Rick Richard]

I only use Second Focal Plane scopes because I zero my scopes at 200 yards and know the drop at 300yds and beyond that I only use a laser range finder and turn the dials. I know that there are specific applications where only a First Focal Plane scope is useful but for hunting I've never understood the whole need for FFP.

I get the whole chest size thing but to me that's pretty inaccurate and I'm not about "good enough" in ranging game. I want to know precisely how far game is from me if it's far enough that bullet drop can become an issue.

I owned a FFP NX8 4-32 scope and found it useless at low power because the reticle nearly disappeared and I couldn't imagine it working for me in a low light situation or one where a quick up close shot would be needed but I'm primarily a hunter and will never compete.

It's more about making adjustments more accurately for WIND calls and not so much about elevation. That is particularly important for a lot of us western or open prairie hunters.

 

[Greyfox]

Decades ago, in my early days of LRH, the SFP was often leveraged for distance shooting and ranging. I used the SFP Leupold scopes with the Boone and Crockett calibrated reticle, effective to 500/600 yards. Depending on your particular loads trajectory profile, the power ring was marked a two power settings that could be used to calibrate the scope. Leupold supplied a variety of load examples. It took a bit of homework and testing, but once it was set up for a particular load it worked quite well for placing the bullet in the vitals in medium sized game out to 500 yards. My ultimate method for calibration that worked better for me was to use a large target that I zeroed at 200 yards using the 200 yard substention . Using this zero, I would shoot the 500 yard target for which the drop was approximately 5 feet, depending on the load. Sighting the target at 500 yards, I would then turn the power ring until the two groups(200 and 500 yard) were matched to the 200 and 500 retical substentions,…and… that was my "marked" power setting for game to 500 yards. The reticle substentions between 200-500 yards were quite close.
The biggest issue back then was to be able to get an accurate range. I graduated to the Redield SFP 3x9 with the AccuRange reticle that used two calibrated stadia lines, matched to the chest it a deer that when lined up could give a decent range out to 500 yards. It also had calibrated, interchangeable Accu-Range turrets of varying configurations to match to caliber/ballistics. It also worked quite well.
This scope/set-up was used by our snipers along wthe the M-40(Remington 308) rifle in Viet Nam. Reliability however, was claimed to be poor in battle conditions.
Technology has surely advanced since then!

 

[cohunt]

Use an app like streelok and you can figure out the drops at every distance/magnification
Examples of same scope at different magnification

At some point the bdc becomes useless and you'll need to dial and use cross hair aim point due to the inaccuracies of the larger aim point on some scopes

 

[osok-1k]

As stated but differently, the primary crosshair will be accurate at your zero range on either reticle design and on any power. If one zero's at 200, it will retain that zero at any available power while using the primary crosshair. In a FFP scope, say you have a shot at four hundred yards, knowing the ballistics and drop of the round you're shooting one can move to the appropriate elevation or vertical hash mark, press the trigger and your on target regardless of power setting. In a SFP scope those hash marks are only accurate at the specified power for the individual scope, unless as previously stated, you've taken the time to calculate and verify point of impact on alternate power settings.

As Coach Jay stated, on a SFP scope there is commonly a dot on the power adjustment ring which corresponds to the power used for accurate ranging. The dots or hash marks in the reticle were intended to be used as a ranging tool. When mil dot and stadia lines were first introduced, nobody had a laser rangefinder and the marks in the reticle were useful tools for that purpose. The introduction of FFP with stadia lines meant that one could accurately estimate range at any power setting.

Dave Miller's approach is also effective in a SFP scope as AZShooter said, but it takes some simple math, knowing your round and it's ballistics, creating a range card with entries for each power setting and as always, verify.

 

[Stonyman88]

As stated in the post I would like to know what happens to your multiple aim points when changing the power . Example: Suppose you sighted in the center cross wire at 100 yds at 10 power the other 3 aim points just happened to fall sighted in at 175, 250, & 325. You did this exact same thing with 2 different scopes both 4-20 power one first & one second focal plane. What happens when the power is changed to say 20 power? Forget about the cross hair being hard to see at low power that's not part of my question here! Will all non center aim points be off the original distances sighted for in : both scopes? only one scope? Or both scopes? If one scope remains sighted correctly at all aim point distances which will it be? I've never used a first focal scope before and know zero about how they function and i like the bdc type reticles! Or at the very least 2 aim points with the duplex type reticle thanks Tribb

I only use FFP scopes now and for the past maybe 20 years, your image as others have said change and along with the reticle, so needing a BDC is a waste of time, just shoot at your yardages and dial up or just use the hash marks, those will be your BDC, so easy, FFP scope with VHR Variable Hunter Reticle, This is the ones I use, check them out, their awesome and unreal how good the glass and they have all the goodies. One sale now around $400 large numbers on the turrets, I have never missed with these scopes, really, unless you wish to spend thousands for the same thing.

 

[Huntaddict]

The FFP is going to be accurate across all powers, the SFP will not if I understand your question correctly. The reticle appears to grow and shrink in a FFP but it's staying the same size. In a SFP the reticle is only accurate at a specific power, whether your measure in mils or moa or using a BDC type system like your talking about.

So only one scope would remain correctly sighted in at all aim point distances, the FFP. I don't believe anybody makes a BDC type reticle in FFP, and for good reason it's much better to just shoot in mil or moa and with FFP you can either dial or hold off the reticle at any power.

Spot on.
I would add for clarity when we talk about the same size, it means that the area between and on the sub tensions stays consistent to the DOPE not matter how large or small the reticle gets. The shooter still places the hash mark on the reticle in the correct spot for the magnification consistent with the distance