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spotter300
Reply with quote  #1 
Ladies and Gentlemen,

I am trying to get in to world of F T/R class shooting, I have hunted my whole life, and would like to try my hand in shooting comps here in Texas. My question is about MOA.

I understand that a 1/4 value for a scope in 1/16th @ 25 yards, 1/4 @ 100, 1/2 @ 200, 3/4 @ 300. However, I am having a hard time with my MOA!

I am going to use the ballistics of my 300 winmag for the numbers, I know it not a F T/R caliber. I will use the drop at 400 yards. I know this is basic for all of you, but I am new to this stuff.

My Hornday Ballistic Calculation goes as follows:

.300 winmag 150 gr.SST with a B.C of .415
400 yard drop is -16.3 inches
I need to come up 3.9 MOA
I know -16.3 inches = 3.9 MOA, but this is the point I get lost.
My click value @ 400 is 1" The bullet drop is -16.3, which would be 16 clicks up to zero or really close to it. 3.9 MOA, how do ya'll figure out your click value? I want to shoot in a 500 yard match, but I can't until I understand the MOA stuff! My 500 yard drop is -33.2 inches ( 6.3 MOA ) Can some shed light on this for me? Please help.

Kevin



effendude
Reply with quote  #2 
Kevin,
I read your post three times, and other than a math error on your 500 yd. MOA which should be 6.64MOA, you have all your answers. Your second sentence explains what your click value should be. A MOA is simply 1" at 100, 2" at 200, 3" at 300, 4" at 400 and so on... A MOA is slightly more than 1" for the techies out there, but for all practical purposes, 1" works until plotting artillery or space travel.

1 click is 1/4" at 100, 1/2" at 200, 3/4" at 300, 4/4" or 1" at 400, 5/4"(1.25") at 500,and 6/4" (1.5") at 600. All assuming your scope is tracking properly. As you can see, 1/4th MOA clicks become very large as distances progress. Many long range and target scopes have 1/8th MOA clicks for this reason.

I simply multiply the yardage times my scopes click value and that is the theoretical movement of one click. Example for 600 yds: (6)X 1/4MOA = 6/4MOA or 1.5" per click. This works for all distances but the math requires some work when the distances are not "whole numbers". 450 yds. is (4.5) X 1/4MOA = 1.13" per click.

Does this help, or did I make it more confusing. This is how I teach my F-class shooters.
Scott
RemVS308
Reply with quote  #3 
Similar to Scott's method, the first thing I'd do is figure out how many inches MOA equals at the target (ex. at 537 yds, 1 MOA = 5.37 x 1.04 = 5.58 inches). Divide your predicted drop in inches by that amount (to get predicted drop in MOA), then figure how many clicks you need to bring it up (multiplying by 4 for 1/4 minute clicks or by 8 for 1/8 minute clicks).

For your 500 yd example, 5 x 1.04 = 5.2 inches = 1 MOA at 500 yds. 33.2 / 5.2 = 6.38 MOA of correction needed. With 1/4 minute clicks, you'd dial up 25 (4 x 6.38) or so clicks; with 1/8 minute clicks, you'd dial up 51 (8 x 6.38) or so.

The click value (1/4 minute, 1/8 minute, or whatever it is) always represents a fixed portion of MOA, no matter what distance the target is... figuring out what MOA equals in inches at the target distance is the only thing you have to do equate inches of drop to clicks on a scope. And if your ballistics calculator is capable of listing drop in MOA, that step isn't necessary - just multiply MOA of drop by your click value.
spotter300
Reply with quote  #4 
Scott,

Yes, the information you gave me helps. However, the math error would be from Hornady. They show 6.3 MOA for a -33.2 drop.

So, based on you info 900 yards would be 9 x 1/4 = 2.25 MOA per click.

Bullet drop of -190.8 inches divided by 2.25 inches per click. I get lost here. -190.8 divided by 2.25 = 84.4


I will PM you my email, for help.
spotter300
Reply with quote  #5 
I not trying to be a pain, I just would like to learn this. Hunting, I know my bullet drop, then I would just hold over. However, since I would like to start shooting comps, it an totally different world, and I want to do it right.
spotter300
Reply with quote  #6 
I would like to thank everyone who responed to this posting. Thanks for the help.

Kevin
FatBoy
Reply with quote  #7 
Let's make this a little simpler. This is how I'd approach this, and what I recommend new 1000 yard shooter at AEDC.

First, visit this site: http://www.jbmballistics.com/~jbm/cgi-bin/jbmtraj-5.0.cgi

Plug in the information for your load. I took your BC of .415, the projectile weight of 150gr. According to the drop you got from Hornady, you have a muzzle velocity of 3600fps (sounds optomistic to me, but maybe not).

You plug these numbers into the program and you check the "std atmosphere and altitude" box. Then click calculate.

The next screen is your come up's in Inched and MOA. Copy this screen, print it out and bring it with you. If you zero the elevation cap on your scope, just dial in the proper MOA for the distance you're shooting. It's not going to be perfect, but you will be on paper if your load is correct. The sighters will allow you to fine tune your elevation and windage. If you can't zero out the turret cap, just count the MOA up from where the scope does zero, it's the same thing, just harder to keep track of.

It's really that simple. Don't think in clicks, think in MOA. Clicks will get you in trouble, especially if you change to a 1/8 MOA or 1/2 moa adjustable scope.

Chris
js223
Reply with quote  #8 
I'm going to second Chris's recommendation of using JBM. I will add a suggestion of picking your bullet from the library (the 150SST is in there), choose the one that says 'Litz' after it, as that means it has a tested BC rather than just the advertised one. Also, if you have chronograph data from your rifle it will help. I've seen factory ammo over 200fps slower than is printed on the box on more than 1 occasion-that will make for inaccurate calculations for sure. With good data, the calculations work very well.
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