Getting started on the math

[Left to Lobster]

I’m far from a expert and new so if there is a better spot to put this I apologize.

Here’s my setup before the questions:

Remington 700 in .308 (Cabela’s special)
1:12 twist
Varmint contour
Cut/crown the barrel from 26 to 20
Diamondback Tactical 4x12x40 single plane
Talley 20 MOA rail
Grayboe stock
Trigger job

I also just picked up a reloading kit - but I don’t have it ready to go.

I have no military or LEO shooting background.

I’ve tested about 8 boxes of ammo of varying brand and weight. It seems to like Federal Powershok 180 gr softpoints.

The range I belong to has the usual amenities plus a 300 and 600 yard range. I have to qualify on the 600y range to shoot on my own. I can hold my own at 300y >

I have problems quantifying the math to “clicks”, looking for some answers/confirmations:

- How much do you trust the FPS / drop data on the box of ammo?

- I just have to assume the ballistics on the box isn’t using a 20” barrel. How do I account for this mathematically? Should I? I assume I need to.

- if I set zero at 100y, I want to shoot 300y. The box says a 17” drop from a 100y zero. If 1 click equals .25 MOA at 100y, then 300y should be .75 MOA per click right? If so, I would adjust the scope 23 clicks, right?

How do I factor in wind drift or should I? At would distance or wind speed is a general rule of thumb for this caliber/ ballistic coefficient?

- I want to and are capable of doing the math. But how I get accurate data like FPS with a 20” barrel without investing a chronograph. Any apps that do that?

- I would like to make ballistics cheat sheet increments of 25y past 100y. Like 325yard = 26 clicks from zero. Dumb idea out 500y?

- any factory ammo worth looking at? Paper and critters?

Thanks!

 

[Wheres-Waldo]

Firstly, I need to ask you about that “trigger job”....

Second, the only way your are going to KNOW the velocity of any given ammunition in your rifle is to chronograph it. Looking up other shooters who shoot that same ammo/barrel length will give you a ballpark, but it may be moderately close at best.

Throw the ballistic information printed on the box in the trash, that’s where it belongs, if you don’t know your velocity, and you want dope at different ranges, the most solid approach is to simply zero at 100 and shoot at different ranges to establish your dope.
After 3+ ranges have solid dope, you can play with a ballistic calculator to get a rough velocity, but nothing is going to be as valuable as a chronograph.

Come-ups
Zero at 100
Shoot at 200 - impact is 5” low
At 200, 5” = 2.25MOA
Your 200 yard dope is 2.25 MOA

Shoot at 300 with 200 yard dope
Impact is 9” low
9” at 300 = 3MOA
3MOA + 2.25MOA = 5.25MOA
Your 300 yard dope is 5.25MOA

I’d suggest a chronograph or at least an educated guess what velocity based on what other shooters are getting. The time and $ saved in ammunition vs. lobbing 20 rounds in a berm trying to figure out where you are impacting will have paid for a chronograph very fast.

 

[pmclaine]

Give your general geographic location and ask the question........

"Where is the nearest precision scoped rifle class?"

 

[Left to Lobster]

On the trigger job, it’s all wall no slob or take up. It’s a little heavier than my Timney featherlite I have in a Mauser I put together. Very nice. Nothing I was capable of doing.

Awesome approach on the ballistics. The missing piece for me.

 

[Left to Lobster]

Give your general geographic location and ask the question........

"Where is the nearest precision scoped rifle class?"

I’m in Michigan. I’m guessing Ohio or Kentucky when I was googling.

 

[pmclaine]

I’m in Michigan. I’m guessing Ohio or Kentucky when I was googling.

Im guessing someone will chime in with some info on where to take a class in Michigan.

Whats the purpose with your rifle?

You just looking to shoot paper for groups?

If 300 and 600 are your distances Id say those are paper and group ranges.

Beyond that you will find peace on steel.

If for those two goals cut all the ammo chasing and just try out Fed Gold Medal Match 168, 175 and perhaps the 185 Juggernaut varieties.

If your gun wont shoot 168 and 175 it is broken - rebuild it.

Here is a picture of a drop chart for Fed Gold Medal 175........

The middle column of information would get you "close".

Think in "Minutes of Angle" not clicks.

So when moving from 100 to 200 yards you add 2.1 Minutes of Angle.

When moving from 200 to 300 you will add another 2.7 Minutes of Angle to your 200 yard DOPE to create a total elevation of 4.8 Minutes of Angle from your 100 yard zero.

Etc.

Example when moving from your set 100 yard zero to 200 yard shooting....

If your scope is manufactured with 1/4 minute ADJUSTMENTS (not clicks) add 2.1 Minutes of Angle or ADJUST the elevation knob 9 times in the up direction. You have added 2.1 MOA elevation.

If you need to correct from that ball park ADJUSTMENT in elevation remember that your corrections are now at 200 yards so your ADJUSTMENT value will double over the longer distance. Each ADJUSTMENT (not click) is now 1/2 inch change in impact.

 

[Left to Lobster]

Whats the purpose with your rifle?

You just looking to shoot paper for groups?

Well I’m a hunter, but if I’m being honest I’ve shot all of my game with a slug gun except for 1 feral pig with a AR. I have aspirations to do some hunting out west or north with it. For the time being it’s a paper puncher.

I can shoot paper at both 100, 200, 300, 600. Steel at 200 and 300.

I’ll pick up some boxes this week and test it out maybe Sunday.

 

[308pirate]

Answers in yellow

Diamondback Tactical 4x12x40 single plane
There is no such thing as a single plane scope. They all have two focal planes. Yours is either first focal plane or second focal plane. That refers to the location of the reticle in relation to the magnifying lenses in the scope. First focal plane scopes have the reticle in front of the magnifier and the reticle is magnified right along with the image. Second focal plane scopes have the reticle behind the magnifying lenses and the reticle is not magnified with the image.

I have problems quantifying the math to “clicks”, looking for some answers/confirmations:
That's because your understanding of angular measurements is fundamentally wrong.

- How much do you trust the FPS / drop data on the box of ammo?
Not much at all but if you don't have a chronograph it will have to do as a starting point.

- I just have to assume the ballistics on the box isn’t using a 20” barrel. How do I account for this mathematically? Should I? I assume I need to.
You're most likely correct that the MV on the box wasn't chronographed out of a 20" barrel. The box should say. And if it doesn't, go to the ammo mfg website and look up the specs for your load. And you still can't find it, assume it came out of a 24" barrel. For compensation to shorter barrels, there are some rough guidelines out there. Some internet searches will turn them up if you use search terms like velocity vs barrel length.

- if I set zero at 100y, I want to shoot 300y. The box says a 17” drop from a 100y zero. If 1 click equals .25 MOA at 100y, then 300y should be .75 MOA per click right? If so, I would adjust the scope 23 clicks, right?
If 1 click equals .25 MOA at 100 yards, it equals .25 MOA at any distance. Minute of angle is not a linear measurement, it's an angular measurement. 1 minute of angle (correctly called minute of arc) = 1/60 of a degree or .0166666 degrees. Every angle subtends a linear distance between the two legs that make up the angle. I'll spare you the trigonometry and will just tell you that at 100 yards, an angle that measures 1 minute of arc subtends (covers) a linear distance of 1.047" (not 1.0"), and .25 MOA subtends 1.047 x .25 = .262" at 100 yards. At 200 yards, 1 MOA subtends 2 x 1.047" = 2.094" and .25 MOA subtends (covers) a linear distance of 0.524", at 300 yards a 1 MOA angle covers a linear distance triple what it did at 100 yards, and so on and so forth. So a minute of angle subtends 1.047 inches per hundred yards. But it's still an angle that measure 1 MOA at any distance. Draw it out on paper if it helps you visualize the concept.

So if your ammo drops 17" at 300 yards from a 100 yard zero how do you know how many minutes of angle you need to dial on your elevation knob? The first step is to figure out how many minutes of angle subtends a 17" linear distance at 300 yards. So at 300 yards, 1 MOA subtends 3 x 1.047" = 3.141". Now take 17" and divide by 3.141" and you get 5.412 MOA. Since your scope adjusts in .25 MOA clicks, you can't dial 5.412 MOA. The closest you can get is 5.5 MOA. 5.5 MOA / .25 clicks/MOA = 22 clicks.

You came close to the correct answer by chance because your basic reasoning (that a click is worth more or fewer minutes of angle as the distance changes) is fundamentally wrong.

How do I factor in wind drift or should I? At would distance or wind speed is a general rule of thumb for this caliber/ ballistic coefficient? Go look up jbmballistics.com and start playing with that. It's free and very accurate if you feed it correct inputs. In the meantime here's a ballpark estimate that works very well with 308 Winchester. Wind drift in MOA for a 10 mph cross wind = range/100 - 1. Range is 750 yards. Your wind drift per 10 mph of cross wind is 6.5 MOA. For a 5 mph cross wind, it's 3.25 MOA. That's all you need right now to get going

- I want to and are capable of doing the math. But how I get accurate data like FPS with a 20” barrel without investing a chronograph. Any apps that do that? In order to get accurate muzzle velocity you need a no-shit chronograph. No ifs ands or buts.

- I would like to make ballistics cheat sheet increments of 25y past 100y. Like 325yard = 26 clicks from zero. Dumb idea out 500y? Not a dumb idea at all. You can use jbmballistics.com for exactly that. And stop using clicks FFS. Get used to thinking in angles, talking in angular measurements, correcting fire using angular adjustments. etc. If you keep thinking in clicks and I give you my 308 winchester rifle you'll be all kinds of fucked because its clicks are worth .1 milliradians or .343 MOA and if you count clicks thinking they're worth .25 MOA you'll miss by a mile.

- any factory ammo worth looking at? Paper and critters?
Hornady match ammo loaded with the 178 grain ELD-X bullet.

 

[pmclaine]

Well I’m a hunter, but if I’m being honest I’ve shot all of my game with a slug gun except for 1 feral pig with a AR. I have aspirations to do some hunting out west or north with it. For the time being it’s a paper puncher.

I can shoot paper at both 100, 200, 300, 600. Steel at 200 and 300.

I’ll pick up some boxes this week and test it out maybe Sunday.

Okay than disregard my advice to get any FGMM ammo.

Go with hunting ammo.

Your ethics will determine how far you shoot and what you require for accuracy on target.

In some ways your goals are easier than precision rifle shooting (in the sense your aimpoint wont be MOA) but when I fail I only have a sucky group.

You fail you have a gut shot animal.

 

[wade2big]

I will be the odd man out. A chronograph is absolutely not needed. Figure out your dope similar to how it was described by a member above. That is all you need. Range target dial the scope to the correct value and hit the target. All the other crap is just that.

 

[300winemag]

MTC Michigan Training Center is a good local facility and they run beginner classes if you are interested.

 

[M8541Reaper]

I will be the odd man out. A chronograph is absolutely not needed. Figure out your dope similar to how it was described by a member above. That is all you need. Range target dial the scope to the correct value and hit the target. All the other crap is just that.

This!
The only time you need a chrono is when you’re trying to get your actual MV. So yes, if that’s what you’re looking for then get a chrono.

However...

For gathering elevation data, you don’t need a chrono, especially at those ranges. All you need is a rough dope chart which can be found by using the one above or googling “20” 1:12 308 _____gr dope chart.”

Get a pen and paper, shoot the generic data at each distance, adjust until you are POA/POI, and then write down your elevation setting. Boom, you’ve just created a dope chart for your system in that particular environment.

You can get a rough MV based on the dope you’ve gathered by “truing” your data in a ballistics app (I’m currently using BallisticsARC and like it a lot). This will also give you more accurate wind data and allow for you to get fairly accurate elevation data for other increments (25yds, 50yds, etc out to as far as you’d like).

The tough dope chart (without truing) you pull will also have rough data for your wind. Unless you’re in crazy conditions and absolutely cannot read wind or mirage, then you shouldn’t have an issue hitting at 600 with a 308 to get your dope.

If you’re only going to punch paper or steel, then i’d run FGMM 168 or 175. If you’re hunting, then make sure you try various hunting rounds and repeat the process for gathering hunting ammo dope.

After you have all of this you can type up the data into an excel spreadsheet and print it out (index card sized), laminate it with 10mm laminate, and tape it to your rifle or throw it in your pocket (...or memorize it).

Despite everything I (and others) have mentioned above, getting actual hands on quality training is the best answer. That being said, make sure you go with a trusted and verified training company/instructor. There are too many con artists out there in this industry and we all work too hard for our money to let an asshat take it.

Best of luck!

 

[Steel head]

This!
The only time you need a chrono is when you’re trying to get your actual MV. So yes, if that’s what you’re looking for then get a chrono.

However...

For gathering elevation data, you don’t need a chrono, especially at those ranges. All you need is a rough dope chart which can be found by using the one above or googling “20” 1:12 308 _____gr dope chart.”

Get a pen and paper, shoot the generic data at each distance, adjust until you are POA/POI, and then write down your elevation setting. Boom, you’ve just created a dope chart for your system in that particular environment.

You can get a rough MV based on the dope you’ve gathered by “truing” your data in a ballistics app (I’m currently using BallisticsARC and like it a lot). This will also give you more accurate wind data and allow for you to get fairly accurate elevation data for other increments (25yds, 50yds, etc out to as far as you’d like).

The tough dope chart (without truing) you pull will also have rough data for your wind. Unless you’re in crazy conditions and absolutely cannot read wind or mirage, then you shouldn’t have an issue hitting at 600 with a 308 to get your dope.

If you’re only going to punch paper or steel, then i’d run FGMM 168 or 175. If you’re hunting, then make sure you try various hunting rounds and repeat the process for gathering hunting ammo dope.

After you have all of this you can type up the data into an excel spreadsheet and print it out (index card sized), laminate it with 10mm laminate, and tape it to your rifle or throw it in your pocket (...or memorize it).

Despite everything I (and others) have mentioned above, getting actual hands on quality training is the best answer. That being said, make sure you go with a trusted and verified training company/instructor. There are too many con artists out there in this industry and we all work too hard for our money to let an asshat take it.

Best of luck!

This.
I remember being in your position OP.
I just shot AR’s and hunted at normal distances.

I was clueless on what was necessary for longer distance shooting.

The above quoted post is a nice easy approach.