FFP vs SFP, zero and zooming

[armypilot]

I have a Rock River AR-15 with a Nikon M223 BDC scope. Shooting Hornady Match red tip 3240 FPU to match the turret. Zeroed at 100 yards. I have made many shots at 200 yards hitting predators. Came up to my dads and tried shooting ground hogs at 400 yards and kept missing with it on 12 power. I had the scoped turret turned to 400 yards. Just messing around dialed it up to 675 yards and hit the target that I had setup (spinner). Now I was really confused. So, I thought maybe the zero was changing with zooming so I put it on 3 power and dialed in 400 yards and hit the target consistently. Any ideas?

I also have a Rock River AR-10 with a Vortex Viper PST FFP 4-16. Zeroed at 100 yards and when I dialed up 16 power and set the turret to 400 yards and was not even hitting the 2 foot x 4 foot plywood at 400 yards. Perplexed on this long range shooting deal.

 

[hunter243sgk]

I have a Rock River AR-15 with a Nikon M223 BDC scope. Shooting Hornady Match red tip 3240 FPU to match the turret. Zeroed at 100 yards. I have made many shots at 200 yards hitting predators. Came up to my dads and tried shooting ground hogs at 400 yards and kept missing with it on 12 power. I had the scoped turret turned to 400 yards. Just messing around dialed it up to 675 yards and hit the target that I had setup (spinner). Now I was really confused. So, I thought maybe the zero was changing with zooming so I put it on 3 power and dialed in 400 yards and hit the target consistently. Any ideas?

I also have a Rock River AR-10 with a Vortex Viper PST FFP 4-16. Zeroed at 100 yards and when I dialed up 16 power and set the turret to 400 yards and was not even hitting the 2 foot x 4 foot plywood at 400 yards. Perplexed on this long range shooting deal.

Don't know the answer but what scope are you using?

 

[slm9s]

"when I dialed up 16 power and set the turret to 400 yards "

What do you mean by, set the turret to 400 yards? I assume you know your velocity. Do you have a custom turret that you can just dial to 400, or do you mean you dialed your 400 yard dope?

I also assume you know that SFP scopes will change reticle subtensions when you change powers. They only range and subtend moa/mil on a specified power. FFP scopes will range correctly on any power setting.

 

[armypilot]

"when I dialed up 16 power and set the turret to 400 yards "

What do you mean by, set the turret to 400 yards? I assume you know your velocity. Do you have a custom turret that you can just dial to 400, or do you mean you dialed your 400 yard dope?

I also assume you know that SFP scopes will change reticle subtensions when you change powers. They only range and subtend moa/mil on a specified power. FFP scopes will range correctly on any power setting.

"when I dialed up 16 power and set the turret to 400 yards "

What do you mean by, set the turret to 400 yards? I assume you know your velocity. Do you have a custom turret that you can just dial to 400, or do you mean you dialed your 400 yard dope?

I also assume you know that SFP scopes will change reticle subtensions when you change powers. They only range and subtend moa/mil on a specified power. FFP scopes will range correctly on any power setting.

The turret on the Nikon is matched to my round see pictures. I don't have to hold over because when I dial the yards in the turret the reticle is adjusted to dad center for those yards. So the fact that it is a SFP should not matter.

 

[FatBoy]

A BDT system is dependant on the BC, muzzle velocity and station pressure. Once you start deviating from this it starts to get less accurate the further you go.

So, I anticipate your next question will make be, why only 400 yards...

Do a scope tracking test, at least an elevation test. Set up a sheet of butcher paper with a dot on the bottom (100y zero) and lines every 3-5 MOA or every MIL. Shoot three shots at your 100y zero to confirm the zero and group size, then dial up whichever MOA/MIL increment you chose, continue to aim at the dot and fire three more, then add the next round of elevation, shoot 3 more on tye dot and so on until you can clearly track where your POI is in relation to your scope adjustments. You need to prove it's tracking before you can go any further.

 

[sawcarver]

Unless I'm missing something it still looks like the turret is in IPHY (very close to MOA) so if you turn it to "4" then you are still probably about 12" low or so. With the PST what did you dial to? Probably needs to be somewhere in the 7 or 7.25 moa to be on at 400

 

[FatBoy]

I didn't see the attached pics. I think sawcarner hit it.

What does your reticle look like? The turret in those pics are not BDC turrets, that is simple MOA on the dial.

Below is a typical matched BDC turret.

 

[sawcarver]

I am guessing the reticle is "calibrated" for the 55gr poly tip. So the scope being SFP probably needs to be on full power to make it follow the distances listed. Nikon's spot on app also lets you see what the values are at different magnifications. Its a pretty good thing to play with when starting down the long range road. Spot on also lets you enter other load data and gives you the values.

I reread your post and you said at 675 you hit the spinner so if the turret is 1/4" clicks at 100 that would be 6.75 IPHY (again almost the same as MOA) and that would be darn close to what I was guessing you needed to dial not knowing your barrel length, elevation etc.

I use an app called Shooter on my phone to help calculate how much to dial.

 

[Geno C]

I am guessing the reticle is "calibrated" for the 55gr poly tip. So the scope being SFP probably needs to be on full power to make it follow the distances listed. Nikon's spot on app also lets you see what the values are at different magnifications. Its a pretty good thing to play with when starting down the long range road. Spot on also lets you enter other load data and gives you the values.

I reread your post and you said at 675 you hit the spinner so if the turret is 1/4" clicks at 100 that would be 6.75 IPHY (again almost the same as MOA) and that would be darn close to what I was guessing you needed to dial not knowing your barrel length, elevation etc.

I use an app called Shooter on my phone to help calculate how much to dial.

This is it. Your reticle is set up for that particular load. Nikon is usually set for max power for it to subtend correctly. The marks on the turret still seem to be in 1/4" per 100yrds per click. As the power goes up and down on a sfp scope, the distance the hash marks subtend from the center changes. The center is supposed to stay put, unless you crank on the turrets.

 

[CharlieNC]

As distance increases the error on your dope goes up exponentially. So the bdc becomes increasingly inaccurate due to differences in bc, velocity, and ambient conditions ( temp, altitude, no, etc). A decent ffp mil,mil scope and a basic ballistic program will pay off immensly in the field and is completely adaptable to all these aspects.

 

[hogpatrol]

As distance increases the error on your dope goes up exponentially. So the bdc becomes increasingly inaccurate due to differences in bc, velocity, and ambient conditions ( temp, altitude, no, etc). A decent ffp mil,mil scope and a basic ballistic program will pay off immensly in the field and is completely adaptable to all these aspects.

Read the entire thread, don't think I missed anything so to the OP, are you assuming YOUR muzzle velocity is what it says on the ammo box? Did you chrono the loads? That number is totally ballpark in the real world. It's a test barrel number and doesn't apply to anything. Chrono the load first, then have a custom turret tape made. As others have said, the BDC reticle is only good for one specific power (in a SFP scope), usually the highest setting. Change the power and it won't work.
Having said that I have a Nikon .223 / 55 gr ballistic/yard setting scope and with factory ammo, I found it's maybe good to 200 yds. after that forget about it. Too much variation in ammo velocities.

 

[Erud]

That does not appear to be a ballistic turret. I believe the load data on the top of the cap only refers to the reticle su tensions. If I am correct, the numbers marked on the turret only refer to the adjustment in MOA from zero, they have no direct correlation to the distance. The zero point on the scope is completely arbitrary, and will depend on how you set the scope up. If dialing to 6.75 is what it took for you to hit what you are aiming at at 400 yards, then that is your setting for 400 yards. Write it down to use as a starting point next time you shoot that distance. You can get apps, etc that will do a pretty good job of telling you how much you need to adjust, but you will always need to verify the data by actually shooting. Write everything down so you do not need to reinvent the wheel every time you go shoot.

Good luck!

 

[Zero333]

Like others said...
Use a chronograph and do a tracking test on the scope. Everything else is just wishful thinking.

The velocity on the box of ammo is from a 26" barrel, maybe a 24" barrel.

Changing magnification power of the scope should not affect the trajectory of the bullet, maybe there is something funky happening with your scope.
I'm not a scope guru, so I can't say what could cause such a thing.

You can just put the original turret back on the scope and gather your own dope with it and the load your shooting. This way you won't have to chrono the ammo or check the tracking of the scope.

Set out targets at different known distances and shoot them. Write down how many clicks or moa or mils you had to dial to hit a target at whatever range you set them out at.

For a 223rem/5.56 shooting a 55gr bullet, I would set up steel targets every 100 yards up to 700yards or just one steel target and move backwards 100 yards at a time writing down the dope as you engage the target in 100 yard increments.

 

[flatlander]

No matter what else you do, first verify whether the scope's tracking correctly. If it's not, none of the other advice given here will help you much. Follow Fat Boy's advice and do a tall target test to find out what the scope's elevation knob clicks are worth; they don't always match the value engraved on the knob. Then find out if it comes back down to your original 100yd zero after you've run it up & back down. Nikon should & probably will stand behind their product if there's an issue with tracking and/or click value matching what's engraved on the knobs.

 

[Turbulent Turtle]

I have a Rock River AR-15 with a Nikon M223 BDC scope. Shooting Hornady Match red tip 3240 FPU to match the turret. Zeroed at 100 yards. I have made many shots at 200 yards hitting predators. Came up to my dads and tried shooting ground hogs at 400 yards and kept missing with it on 12 power. I had the scoped turret turned to 400 yards. Just messing around dialed it up to 675 yards and hit the target that I had setup (spinner). Now I was really confused. So, I thought maybe the zero was changing with zooming so I put it on 3 power and dialed in 400 yards and hit the target consistently. Any ideas?

I also have a Rock River AR-10 with a Vortex Viper PST FFP 4-16. Zeroed at 100 yards and when I dialed up 16 power and set the turret to 400 yards and was not even hitting the 2 foot x 4 foot plywood at 400 yards. Perplexed on this long range shooting deal.

Did you ever get this resolved? I read the thread and I have a few questions.

I believe you have the Nikon M-223 3-12X42SF BDC 600. Unless you got custom knobs made for it, the knobs on that scope are in 1/4 inch per hundred yards. The BDC in the reticle (the circles) are designed to subtend at distances for the ammo printed on the scope knob. The numbers of the elevation knob are NOT hundreds of yards; they are IPHY values (close to MOA). So when you dialed 675 yards, you actually came up 6.75 IPHY (or 6.75 MOA) from your 100 yard zero and that was enough to get on target at 400 yards.

The BDC circles on the reticle represent different distances depending on the magnification you use, as well as the ammo you use. You need to read about SpotOn at Nikon USA website to get the distances for the various magnifications. On the other hand, using the knob for elevation is not dependent on the magnification, it just adjusts the center crosshair that number of IPHY, up or down and side to side.

If you want to use the BDC, you need to pick a magnification and zero at that magnification and shoot at that magnification from that point forward, unless you can remember what the offsets are at different distances and magnification. For longer range where you will want to use 12X, I would set the zero at 12X and memorize the meaning for each circle at 12X.

In an SFP the BDC will always change with the magnification. But in an SFP or FFP, the elevation knobs is not influenced the magnification for the central crosshair.