Home Forums Hunting & Shooting Hunting Optics How to use that new SWFA scope- reticle, turrets and proper usage.

I have already sighted in my SS 6x42MQ and admit to converting inches to mils for the adjustment. I was only 1" low and 1" left. I adjusted to be 2" high at 100 yards. Next two shots straddled the verticle line 2" high. The adjustments were very precise. I am not used to that.

I had a little trouble determining which reticle mark was over the initial bullet hole but could easily see the grid marks on my target. That's why I converted inches to mils.

One question, if I refocus the eyepiece to make the reticle sharper will my point of impact be affected? Does it depend on the quality of the scope or what?

Thanks for the post. Lot's of information.

Nice!!





Take care, Willie

Thanks a hundred times. Wondered about the correction factors too. So - on a scope with 1/4 MOA adjustments I'd input, what?


Care to go into some atmospheric inputs on the Shooter app? Absolute? ASM? ICAO? Enable Zero Atmosphere? MV Variation?

Great post, Form! Nicely done with the pics and simple steps. I thought I might add a couple of thoughts to hopefully give additional clarification.

1. For anyone struggling to make the transition to thinking it terms of MRAD instead of inches, let's talk angular measurement for a minute. Mils (MRAD) sound weird and unfamiliar to most guys. It's really just an angular unit like degrees are, so let's call them degrees for this explanation. Most guys can picture a 15 degree or a 45 degree angle in their heads- it's a unit of measure that we're familiar with. Let's suppose you were throwing a baseball or football to a friend that is 50 yards away. You'd need to aim your throw up in the sky at perhaps a 35 degree angle in order to land the ball in your friend's hands. If your throw hits a little low, say at your friend's feet instead of at his chest level, you're not going to say to yourself, "okay, that hit 4 feet low, so at 50 yards 4 feet translates into 9.6 degrees, so I'd better aim my throw another 9.6 degrees higher, for a total angle of 44.6 degrees, in order to land the ball at chest level", you're just going to intuitively aim the throw at a little steeper angle, and it'll hit higher on your friend's body. Well this is similar to converting inches to MOA or MRAD when shooting. It's just a bunch of extra thinking and work to be converting back and forth between linear and angular units, when you could just think in terms of the angle. Unlike the baseball/football, you're not going to adjust your rifle intuitively (Kentucky windage), instead you're going to use an optical, angular ruler (reticle) to measure the adjustment angle needed, and instead of 9.6 degrees, it'll be 0.2 or 1.5 MRAD, or something similar.

There are 360 degrees in a circle. Now instead of picturing a circle that's flat on the ground like a compass, picture a circle that's standing vertical like a Ferris wheel. You can imagine that circle being marked with 360, 1-degree tick marks all around its circumference. Now instead of imagining 1-degree tick marks, imagine that the circle is divided into 6 slices (well 6.28 to be more exact), and the tick mark on each slice is called a 1-radian mark. Now picture each of those slices being divided up into 1000 pieces, and each of those little pieces is approximately a milliradian (MRAD for short). When you adjust 1 MRAD, you're adjusting the angle by one of those tiny slices. Now with that out of the way, let's go back to degrees. If you change the angle of your football throw by 1 degree, that's a 1 degree change whether your friend is standing 10 yards away or 50 yards away. Of course a 1 degree change will land the football only 1" higher at 10 yards, but would land the ball 5" higher at 50 yards. Now if you had an optical angular ruler and could watch the ball land low, you'd be able to measure the angle you need to adjust your throw by, and could try to throw 9.6 degrees higher (your arm doesn't have adjustable turrets on it, unfortunately). So whether your target it as 10 yards or 50, if you see a 1 degree correction is needed, it's 1 degree. If your target is at 10,000 yards and you see in your angular ruler that you need a 1 degree angle correction, that means you need 1 degree. Same with MRAD. If your reticle shows 1 MRAD correction needed, that's the same at 100 yards or 500. Of course that would translate into 3.6" at 100 yards and 18" at 500 yards, but we don't need or want to translate. Keep it in MRAD and keep life simple. One MRAD.

Now we often measure group size in MOA because of industry standard convention, but we could easily use MRAD for that too, except that nobody would know what we were talking about Aside from that, measuring target size, windage hold-off, shot correction, lead for a moving target, etc, are all measured/held using MRAD.

2. To the guys noticing that the elevation and windage correction factors are set to "1", this is something that needs to be verified if you're using your scope for shooting much beyond 500 yards. If your turret adjustments are 100% perfect, then the correction factor should be set to "1". If the actual adjustment is 0.99 mil per 1 mil (10 clicks) dialed instead of the advertised 1 mil per 10 clicks, then your correction factor should be set to 0.99. You'll need to verify whether your specific ballistic app uses the correction factor as the ratio of actual to advertised adjustments, or advertised to actual. With Ballistic:AE it's actual to advertised, so if you find that your turret adjusts 0.102 mil per click instead of the advertised 0.1 mil per click (1.02 mil actual adjustment for 1 dialed mil, if you dialed in 10 clicks), then the correction factor should be set to 1.02 (a ratio of 1.02 actual divided by 1.00 advertised). This can be measured and verified using a Tall Target test with an accurate rifle, as well as by setting up your scope in a fixture and testing tracking, or alternatively by measuring your reticle against a set subtension target at a set distance (to make sure your reticle is an accurate baseline), and then using an optical grid like the Bushnell magnetic boresighter to check that your turrets track properly as measured with your reticle. DON'T do this for your windage turret if you plan on using your reticle for windage holdoffs, that's assuming your reticle subtends true to form, as verified when doing the Tall Target test. Since we're using the reticle for windage, we don't care all that much what the turret does, and we want our ballistic app to spit out wind holds using the correct subtension of the reticle, not corrected for the actual adjustment increments of the windage turret. So if your reticle reads 5 MRAD, and that is truly 5 MRAD, leave the windage correction factor at "1".

This ensures that the ballistic app is telling you to adjust the ele. turret the correct amount, given how much each click is actually moving the reticle. At closer distances a 1 or 2% error isn't going to make a whole lot of difference in your shot solution (eg. 2.0 mil versus 2.04 mil), but can start to stack up when dialing in larger correction values.

Another excellent post.

This thread should be a sticky at the top...............

The correction factor really just refers to the percent error of your turret's actual adjustments compared to advertised. So if you select 1/4 MOA adjustments in Shooter or Ballistic:AE or any other good app, and your turrets truly adjust 0.25 MOA, then you'd leave the correction factor as "1". If it adjusts 0.23 MOA, then you'd enter 0.92 in for the correction factor. If one click adjusts 0.27 MOA, you'd enter 1.08, and so on. EDIT: This is how Ballistic:AE works, which is what I use, but it looks like the Shooter app does the inverse of this. So with Shooter, if your turret actually adjusts 0.23 MOA, you'd enter 1.087.

Absolute pressure refers to whether you're entering the actual air pressure compared to a vacuum, or if you're entering air pressure corrected for sea level. If you're located a few thousand feet above sea level, and you see a reading of 29.92 InHg, then you're reading relative, gauge, or barometric pressure. If you look at your Kestrel and see a reading of 25.62 InHg, then you're reading absolute pressure. Absolute pressure read off of a handheld device is preferred, as it bypasses conversions and local weather station input. FYI, if you have an iPhone 6 or newer, your phone has an air pressure gauge built in, and you just have to get the "Barometer" app to get absolute pressure readings from your phone without having to use a Kestrel or similar.

Enable Zero Atmosphere means that your app will compare your current shooting atmospheric conditions with the conditions present when you zero'd the scope with that load, and will calculate the difference in your zero for use in your current shot solution. If this is clicked off, the app just leaves your zero the same for any atmospheric condition.

I use Ballistic:AE instead of Shooter, so I'm not 100% sure, but I'm guessing that MV variation is a measure of the temp sensitivity of the powder you used in your load, and how much the MV changes for each degree F in temperature change.

ASM and ICAO are just two different atmospheric standards that bullet companies reference when advertising BC values. The Shooter app manual says this: "Berger, Nosler and Lapua all use ICAO. Sierra, Barnes, Hornady and Winchester use ASM". Not a big deal which you select, as it doesn't make a big difference.

The manual can be found here: https://www.shooterapp.net/manual.php

Note: Read the manual for whatever app you use, as the terminology used between different apps can refer to different things.

Thank you!

This and your previous post regarding proper scope mounting is undoubtedly the best posts in the Optics Forum in a looooooong time!

Kudos

Thanks for the posting Formidilosus, I have a Burris 2-10x42 XTR II and I love the mil radian turrets. Your write up is basically what I do. Site in at 100 yards and use the JBM Ballistics program. I only have access to a 500 yard range, but it works like a charm out to there.

If you are shooting at 200 yards (or further) instead of 100 can you use the reticle in exactly the same way, i.e. - just read the mils on the target and adjust accordingly to move POI to zero? Or is there some conversion? So far I've only shot my 10X at 100 yards so I haven't tried this.

I addressed this in my first post in this thread. The angle measured with your reticle is the same no matter what distance the target is at.

Very nicely explained. I'll be linking to this.

ILya

Thanks Jordan and I bet Formi thanks you too for saving him the key strokes!

Great stuff guys!

Thanks Jordan! Sorry, I didn't read all of your previous post. And thanks to Formi for the original writeup.

Tag

All of Form’s post holds true for ffp MOA scopes as well. Only difference is you would set adjustments to be .25 and swap it to moa

Great post Form, thanks much!

Now, I guess I'll have to get a smart phone.

And if you did that you'd be wrong. You've just illustrated why Mils is superior to MOA. A Mil is always a Mil, but 1" is not the same as 1 MOA. Just like 0.25" is not 1/4 MOA . 0.261" is 1/4 MOA. (one MOA = 1.047") It may not seem like much, but when you shoot long range small errors compound.

IPHY is Inch Per hundred yards and is also called SMOA.

Let me illustrate: 6.5mm 147 Grain Hornady ELD M @ 2800 FPS. I'll calculate both in MOA (1 MOA = 1.047") and 1 IPHY = 1.0" at 100 yds.

Drop in MOA @ 1000 yds. is 27.2 MOA

Drop in IPHY @ 1000 yds 28.5"

The difference is 1.3 MOA @ 1000 yds or 13.61". That a pretty large error and could be a big miss.

Windage in MOA @ 1000 yds 5.8 MOA

Windage in IPHY @ 1000 yds. 6"

That's only a net difference of 0.2 MOA or 2.1" Not much difference because it was compounded less.

Thanks to Form and Jordan for the schooling!

Sticky this please!

Also, sticky Form's scope mounting thread.