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Scope question

Posted By: Mike in A-town

Scope question - 09/20/20 01:08 AM

I mounted a 4-32x50 on my 308. Scope is second focal plane.

It's zeroed at 100 yards and my latest target is set at 700 yards... Ballistic math says 5.5 mils of drop at 700 yards. If I leave the magnification at the lowest setting I can hit the target with a decent amount of regularity. But if I bump up to full magnification then I am completely off the map.

Is there a formula to determine my elevation adjustment when using higher magnification?

I ran a little test to see if my assumptions were somewhat correct:

1 mil at 100 yds is 3.6" So I divided 100 by 20 and of course got 5 yds. 3.6" divided by 20 is .18"

So I set up a target at 5 yards with two lines .18" apart and checked it with the scope at 4 power. It measured 1 mil. Then when I increased the magnification to 32 it measured 8 mils... That made sense. So I assumed at full magnification that 1 mil equals 8 mils, right?

So if that math was correct then I would need to divide my 5.5 mils by 8 and get .675 mils... So I held as close as I could (between .5 to 1 mil) and was still off the map.

Was I completely wrong with the math?

My 300 Win Mag has a FFP scope on it and doesn't change when magnification is increased... Much easier to use but a little more expensive.

Any help or advice would be greatly appreciated.

Mike
Posted By: 330-Trapper

Re: Scope question - 09/20/20 01:14 AM

I'm bad with math... good thing I get closer when I hunt.
Sorry no help.
Posted By: robert.d12

Re: Scope question - 09/20/20 01:26 AM

Yes, your reticle change as you change the magnification. Usually a reticle is designed for max magnification, but on a 32x scope it might not be. What brand and model is it? You should be able to google what magnification the reticle is set for
Posted By: keystone

Re: Scope question - 09/20/20 01:47 AM

Are you using the hold over marks on your scope or adjusting the turrets? If your using the turrets to adjust the main crosshair there should be no deviation no matter what magnification. If your using holdover marks then you would need to shoot at the same magnification that you sighted the rifle in with at that particular distance.
Posted By: keystone

Re: Scope question - 09/20/20 01:51 AM

Originally Posted by robert.d12
Yes, your reticle change as you change the magnification. Usually a reticle is designed for max magnification, but on a 32x scope it might not be. What brand and model is it? You should be able to google what magnification the reticle is set for


On a SFP the reticle does not change, the target does. The reticle is placed behind the magnification lense so it never changes size.
Posted By: Mike in A-town

Re: Scope question - 09/20/20 01:53 AM

Originally Posted by keystone
Are you using the hold over marks on your scope or adjusting the turrets? If your using the turrets to adjust the main crosshair there should be no deviation no matter what magnification. If your using holdover marks then you would need to shoot at the same magnification that you sighted the rifle in with at that particular distance.


Holdover.

Mike
Posted By: Boone Liane

Re: Scope question - 09/20/20 01:59 AM

If youíre using the reticle marks as holdover points, you need to remember the subtensions change with magnification in a second focal plane scope.

Most reticles are calibrated for max power, but some are not.

A one mil mark on high power (or the calibrated magnification point), will be two mils at half that power.

Posted By: Leftlane

Re: Scope question - 09/20/20 02:14 AM

They have phone apps that will do all the math for you now.
Posted By: JD Hornet

Re: Scope question - 09/20/20 02:22 AM

What is the brand of scope and welcome to long range shooting it ain't simple do your home work.
Posted By: keystone

Re: Scope question - 09/20/20 02:23 AM

Originally Posted by Mike in A-town
Originally Posted by keystone
Are you using the hold over marks on your scope or adjusting the turrets? If your using the turrets to adjust the main crosshair there should be no deviation no matter what magnification. If your using holdover marks then you would need to shoot at the same magnification that you sighted the rifle in with at that particular distance.


Holdover.

Mike


So you have to think about the target changing size as you increase and decrease the magnification, the reticle does not change size. When your sighting in for 700yds you have to use the exact holdover mark at the exact magnification that you will always use at that particular distance. The distance between your holdover marks stays the same since your reticle doesnít change size but your target gets much larger at higher magnification.
Posted By: Mike in A-town

Re: Scope question - 09/20/20 02:46 AM

Originally Posted by Leftlane
They have phone apps that will do all the math for you now.


Yep, I just used the free one at gundata. It already had a chart for the factory loads i was shooting. I dont know what barrel length they used and I don't have a chrony to know my MV but the chart stated 138" drop at 700 yards... So that translated to 5.5 mils. That's what I held at and was able to hit 5 out of 8 so it had to be pretty close.

The gun is an AR10 so I doubt I'll ever have ragged hole/cloverleaf accuracy, but I'll push it as far as I can.

And you never realize how lousy and inconsistent factory ammo is until you start reaching out there. Handloads are next, but that will mainly be for the 300WM. I just don't see a production AR platform grouping as well as a decent bolt gun.

Mike
Posted By: Leftlane

Re: Scope question - 09/20/20 02:54 AM

I haven't downloaded it but a guy was at my buddies shop was showing us his app that calculated everything including your barrel length and a huge number of factory loads. I myself like walking it in but yeah- I am not much of an ammo conserver and never have been
Posted By: Mike in A-town

Re: Scope question - 09/20/20 02:59 AM

Originally Posted by JD Hornet
What is the brand of scope and welcome to long range shooting it ain't simple do your home work.


Sightmark Wraith. No real windage and elevation adjustments to be made with it... I can adjust my zero but that's about it. Pretty sure it's mainly for varmint/hogs... It's NV capable and has an IR emitter so I KNOW that's what it's for. But it's fun to play around and see what can be done.

And yes, the LR shooting bug seems to have bit me. But any serious attempts at it will be done with my bolt gun... which isn't a specialized LR rig either... But it's all I have right now.

I may have to save up and get a decent rig but I'll never shoot competitively... I just want to see how far I can reach out and ring gongs... To see if I can.

Mike
Posted By: Mike in A-town

Re: Scope question - 09/20/20 03:06 AM

Originally Posted by Leftlane
I haven't downloaded it but a guy was at my buddies shop was showing us his app that calculated everything including your barrel length and a huge number of factory loads. I myself like walking it in but yeah- I am not much of an ammo conserver and never have been


Oh yeah, there's a million of em.

I'll completely geek out over ballistics... My wife has threatened to smother me in my sleep if I keep discussing it. Lol

Mike
Posted By: LAtrapper

Re: Scope question - 09/20/20 03:18 AM

A link to this article was suggested in a similar discussion recently- https://www.americanhunter.org/articles/2017/7/10/first-focal-plane-or-second-focal-plane/
Posted By: Mike in A-town

Re: Scope question - 09/20/20 03:21 AM

Originally Posted by keystone
So you have to think about the target changing size as you increase and decrease the magnification, the reticle does not change size. When your sighting in for 700yds you have to use the exact holdover mark at the exact magnification that you will always use at that particular distance. The distance between your holdover marks stays the same since your reticle doesnít change size but your target gets much larger at higher magnification.




I think I understand what you're saying. Here's what I'm trying to wrap my head around...

When I zoom from 4x to 32x my target gets 8 times bigger. This was evidenced by my little 5 yard experiment.

Now if I'm at 700 yards and using 4x power and hitting with 5.5 mils of holdover and I zoom to 32x my target is now 8x bigger than it was at 4x. So is it correct to think that I would divide my 5.5 mil holdover by 8 to account for that? The math would seem to make that right but that's assuming it's proportional.

Or is it easier/more accurate to move back to 100 yards and rezero at 32x and go from there?

Mike
Posted By: Mike in A-town

Re: Scope question - 09/20/20 03:29 AM

Originally Posted by LAtrapper
A link to this article was suggested in a similar discussion recently- https://www.americanhunter.org/articles/2017/7/10/first-focal-plane-or-second-focal-plane/


Yep, I read that a while back. No one ever offers a formula they just tell you that the math with SFP is complicated... And they're right.

I'm a huge proponent of FFP it's just a million times easier to compensate. SFP seems to be fine for about 300 yds and under because any change in magnification isn't going to shift your POI enough to matter at those ranges.

But I've got this ONE sfp scope. Lol

Mike
Posted By: GREENCOUNTYPETE

Re: Scope question - 09/20/20 03:35 AM

what load are you using Mike?

in a second focal plane typically the only place the Mil dots or MOA depending on what it is at max magnification however some are not when you get above 12 power there is sometimes a mark for where the calibration point is.

is this the scope? https://www.foxoptic.com/product-review-sightmark-wraith-4-32x50-digital-day-night-scope/

is yours the digital scope?

if it is are you sure you are on the Mrad reticent as it looks to have 9 options with some mrad and some moa

for many of us it is easier to think in MOA than MRAD you may have options.

if you made a 10 centimeter square and placed it at 100 meters it should measure 1 mrad you may want to make a 55 centimeter square that should measure 5.5mrad at 100 meters to check calibration.
Posted By: Mike in A-town

Re: Scope question - 09/20/20 03:49 AM

I'm getting ready to turn in Pete. I'll get back to you. Loads are Federal American Eagle 150 gr FMJ. No particular reason for using that load its just what I had the most of on hand.

Mike
Posted By: Mike in A-town

Re: Scope question - 09/20/20 03:59 AM

Yes Pete, that's it. And I am using the MRAD reticle with the dot in the center... I believe it's reticle #1 in the link you shared.

Mike
Posted By: 330-Trapper

Re: Scope question - 09/20/20 04:21 AM

Originally Posted by Leftlane
They have phone apps that will do all the math for you now.

It won't help me....to Old syndrome grin
Posted By: EdP

Re: Scope question - 09/20/20 12:28 PM

I have several second focal plane scopes that are equipped with subtended reticles (Vortex and Leupold). A graphic showing the mil/moa dfference for each subtension as compared with the crosshairs (at max magnification) was available on line from each mfg's site.
Posted By: seniortrap

Re: Scope question - 09/20/20 12:37 PM

In measuring degrees there is a reference. Using a circle at 360 degrees.

For every inch (1) a degree is .0175". That's of an inch. 12 inches of one degree measures .21".

One degree at 120 inches its 25.2" So at 100 yards a degree is moving 63 feet. 1/4 moa is 15.75.

Now everyone can figure that out further.
Posted By: GREENCOUNTYPETE

Re: Scope question - 09/20/20 02:28 PM

Originally Posted by Mike in A-town
Yes Pete, that's it. And I am using the MRAD reticle with the dot in the center... I believe it's reticle #1 in the link you shared.

Mike

being digital I am not sure the conventional rules apply the same

as a second focal plane unless otherwise stated generally highest magnification is where the recital is calibrated

I think I would set up a calibration square of say 30 centimeters place that at 100 meters and then proceed to see how the calibration actually is in the scope
Posted By: keystone

Re: Scope question - 09/20/20 03:05 PM

Originally Posted by Mike in A-town
Originally Posted by keystone
So you have to think about the target changing size as you increase and decrease the magnification, the reticle does not change size. When your sighting in for 700yds you have to use the exact holdover mark at the exact magnification that you will always use at that particular distance. The distance between your holdover marks stays the same since your reticle doesnít change size but your target gets much larger at higher magnification.




I think I understand what you're saying. Here's what I'm trying to wrap my head around...

When I zoom from 4x to 32x my target gets 8 times bigger. This was evidenced by my little 5 yard experiment.

Now if I'm at 700 yards and using 4x power and hitting with 5.5 mils of holdover and I zoom to 32x my target is now 8x bigger than it was at 4x. So is it correct to think that I would divide my 5.5 mil holdover by 8 to account for that? The math would seem to make that right but that's assuming it's proportional.

Or is it easier/more accurate to move back to 100 yards and rezero at 32x and go from there?

Mike


Like you said as long as your holdoverís are proportional that would make sense but i would definitely think it would be easier to move back and zero at 32 power, or whatever power you would feel you would use from say 300 out to 700. SFP is perfectly fine when adjusting with the turrets, when using the holdover it becomes a pain in the butt, especially because the holdovers donít account for wind. Instead of having a 4-32 power scope itís like you have a 4 power and a 32 power. Or a 4 power and whatever other power you choose. Thereís to much complication in between.
Posted By: Boone Liane

Re: Scope question - 09/20/20 03:07 PM

Ahhh, an electric scope.

It would not be out of the realm of possibilities to be a true mechanical (or in this case, electrical) issue.

OLED reticle and all.
Posted By: Boone Liane

Re: Scope question - 09/20/20 03:09 PM

Personally, Iíve never looked through a FFP scope where the reticle was actually usable across the entire magnification range.

To small and worthless to see at low power, large, cluttered, and obtrusive to the sight picture on high power.
Posted By: jbyrd63

Re: Scope question - 09/20/20 04:28 PM

Originally Posted by robert.d12
Yes, your reticle change as you change the magnification. Usually a reticle is designed for max magnification, but on a 32x scope it might not be. What brand and model is it? You should be able to google what magnification the reticle is set for


WHAT !!! About this time last year I had the same problem but not at that distance and I was told no way. Changing magnification doesn't effect zero....
Posted By: Mike in A-town

Re: Scope question - 10/12/20 01:52 AM

Quick update...

It looks like the biggest problem was the ammo. I stated earlier that I was using Federal American Eagle 150 gr FMJ. They just don't shoot well in the gun. So I worked up some hand loads with Nosler 150 gr. Ballistic Silvertips. Best group was about 1.5" at 100 yards. Still not good enough.

So I researched and asked around. I was told to try heavier bullets so I picked up some Sierra Match King 168 HPBT. I loaded 10 to try out... 5 at the starting load and another 5 loaded at the mid range. Went out and shot them at 100 this afternoon...

Still have to fine tune the load some but the groups were much better. I had a few fliers which is probably me being jerky on the trigger. Without the fliers my groups were about 1/2"

If I can tune the load and keep my groups at 1/2" I'll start working back up to that 700 yard target... 700 is just about the max I can safely shoot at this spot.

I may look into upgrading my trigger too. The factory trigger breaks pretty clean but it feels like it takes about 14 pounds to make it break.

Mike
Posted By: GREENCOUNTYPETE

Re: Scope question - 10/12/20 03:17 AM

good to hear it is getting better

I found my 1:10 twist 308 didn't much care for 150 federal either , they were about 2 1/2 inches at 100 yards

this was from bolt action rifles

the 165 and 180 were better
Posted By: nvwrangler

Re: Scope question - 10/12/20 03:47 AM

Originally Posted by keystone
Originally Posted by robert.d12
Yes, your reticle change as you change the magnification. Usually a reticle is designed for max magnification, but on a 32x scope it might not be. What brand and model is it? You should be able to google what magnification the reticle is set for


On a SFP the reticle does not change, the target does. The reticle is placed behind the magnification lense so it never changes size.



This
First focal plane the reticle changes size
Second focal plane it stays the same size but is normally only correct at the highest magnification for moa or mill
Posted By: Mike in A-town

Re: Scope question - 10/12/20 11:33 PM

Originally Posted by GREENCOUNTYPETE
good to hear it is getting better

I found my 1:10 twist 308 didn't much care for 150 federal either , they were about 2 1/2 inches at 100 yards

this was from bolt action rifles

the 165 and 180 were better



It was a substantial improvement.

I have some Hornady 195 gr ELD Match bullets and a pound of CFE 223... I may load up 5 or 10 just to see how well they shoot just for kicks.

Mike
Posted By: GREENCOUNTYPETE

Re: Scope question - 10/12/20 11:41 PM

I like to load 180 BTSP but I got a good price on a Few 165 BTSP they work on deer also heck inside 200 I don't know if I or the deer can tell

if this bullet shortage lasts a long time I will be shooting 165 for closer targets and save some 180 for when I feel I need the extra weight

I load H4895 not the highest velocity but works in the M1 , 308 , 223 , 30-30 it does a decent job
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