AR Sponsor
Posted: 1/11/2015 1:10:59 PM EDT
|
I have a Swarovski 3-9x36 with a 4A reticle. The subtend from the center to the top of the bottom post is 8.3" at 100 yards. If I zero my AR with 55r V-Max at 100 yards, the trajectory drop for 8.3" corresponds with 265 yards. I assume if I aim at a bullseye at 265 yards with the top of the post, I should hit it. But if I zero it at 200 yards, the drop for 8.3" is 298 yards, but the poi at 100 yards is +1.4". Do I subtract the 1.4" from the 8.3" and use the drop for 6.9" which is 286 yards? Thanks.
|
|
Quoted:
I have a Swarovski 3-9x36 with a 4A reticle. The subtend from the center to the top of the bottom post is 8.3" at 100 yards. If I zero my AR with 55r V-Max at 100 yards, the trajectory drop for 8.3" corresponds with 265 yards. I assume if I aim at a bullseye at 265 yards with the top of the post, I should hit it. But if I zero it at 200 yards, the drop for 8.3" is 298 yards, but the poi at 100 yards is +1.4". Do I subtract the 1.4" from the 8.3" and use the drop for 6.9" which is 286 yards? Thanks. Short answer is no. Drop does not increase linear with distance, it's an exponential relationship. |
|
Quoted: Short answer is no. Drop does not increase linear with distance, it's an exponential relationship. Quoted: Quoted: I have a Swarovski 3-9x36 with a 4A reticle. The subtend from the center to the top of the bottom post is 8.3" at 100 yards. If I zero my AR with 55r V-Max at 100 yards, the trajectory drop for 8.3" corresponds with 265 yards. I assume if I aim at a bullseye at 265 yards with the top of the post, I should hit it. But if I zero it at 200 yards, the drop for 8.3" is 298 yards, but the poi at 100 yards is +1.4". Do I subtract the 1.4" from the 8.3" and use the drop for 6.9" which is 286 yards? Thanks. Short answer is no. Drop does not increase linear with distance, it's an exponential relationship. Thanks for the reply, what does that mean in simple terms? Do I use the 298 yards with a 200 yard zero? |
|
A very basic thing to remember is an adjustment on your scope at 100 gets multiplied by the distance your shooting at......
That 8.3 " your talking about will be 24.9 at 300yrds doesn't matter where you zero our scope for..... it will be 16.6 at 200 ...... 83 at 1000 This is a good basic place to start... http://www.millettsights.com/resources/shooting-tips/calculating-mil-dot-reticle-holdovers/ eta this too... http://www.millettsights.com/resources/shooting-tips/target-knob-settings/ |
|
Partial answer - Use any of the ballistics online tools to chart your trajectory. This will tell you exactly how many mils (or MOA) your round drops from your zero point for any given yardage. This would let you determine where your bullet will cross the line of your bottom post.
As the speed drops off of the projectile it travels a shorter distance for every inch of drop. The decrease in speed isn't a constant but a variable change based on a lot of factors, shape, drag, mass, coefficient, air density, wind etc. This is what gives it that arc light path. It's dropping at a constant velocity, just variable speed makes it travel an ever decreasing distance at any given point in the path. For practical purposes you should be able to find a good zero that will get you +/- about 3 inches out to 300 yards. In fact just for S&G's I went to hornady's quick ballistics page and assuming you're running 3200 FPS on those 55gr Vmax's with a .255 BC out of your rifle a 25yard zero puts you around +3 inches at 100 yards, +3.7 inches at 150 yards, +0.0 at around 270 yards and -2.6 inches at 300 yards. Your bottom post would be zeroed somewhere around 352(ish) yards where it should be about - 8.3 inches give or take a hair. Not sure what you're shooting for in terms of precision or targets but that should get you pretty close to a DRT shot on most animals out to 300 yards and certainly something like a 8" plate without having to worry about adjusting your POA assuming you do your part and your system shoots under 3 MOA. |
|
Quoted:
I have a Swarovski 3-9x36 with a 4A reticle. The subtend from the center to the top of the bottom post is 8.3" at 100 yards. If I zero my AR with 55r V-Max at 100 yards, the trajectory drop for 8.3" corresponds with 265 yards. I assume if I aim at a bullseye at 265 yards with the top of the post, I should hit it. But if I zero it at 200 yards, the drop for 8.3" is 298 yards, but the poi at 100 yards is +1.4". Do I subtract the 1.4" from the 8.3" and use the drop for 6.9" which is 286 yards? Thanks. What ya doing? Trying to figure out a zero that will allow use of post as a holdover? The top of post will be about 500 +/- ?? yards for 50, 100, 200 & 300 yard zero's(I think, I didn't punch anything in) The sooner you learn to use 'iStrelok' the smarter you will appear. 
TTC |
|
Your math is all kinds of wrong.
It also looks like you set that ballistic chart at a 1.5" scope height ....... pretty unlikely for an AR Quoted:
Partial answer - Use any of the ballistics online tools to chart your trajectory. This will tell you exactly how many mils (or MOA) your round drops from your zero point for any given yardage. This would let you determine where your bullet will cross the line of your bottom post. As the speed drops off of the projectile it travels a shorter distance for every inch of drop. The decrease in speed isn't a constant but a variable change based on a lot of factors, shape, drag, mass, coefficient, air density, wind etc. This is what gives it that arc light path. It's dropping at a constant velocity, just variable speed makes it travel an ever decreasing distance at any given point in the path. For practical purposes you should be able to find a good zero that will get you +/- about 3 inches out to 300 yards. In fact just for S&G's I went to hornady's quick ballistics page and assuming you're running 3200 FPS on those 55gr Vmax's with a .255 BC out of your rifle a 25yard zero puts you around +3 inches at 100 yards, +3.7 inches at 150 yards, +0.0 at around 270 yards and -2.6 inches at 300 yards. Your bottom post would be zeroed somewhere around 352(ish) yards where it should be about - 8.3 inches give or take a hair. Not sure what you're shooting for in terms of precision or targets but that should get you pretty close to a DRT shot on most animals out to 300 yards and certainly something like a 8" plate without having to worry about adjusting your POA assuming you do your part and your system shoots under 3 MOA. |
|
I'm shooting factory .223 55gr Hornady V-Max out of my AR and my velocity is about 2900 fps with a 16" barrel. The center of the scope is about 2.7" above the center of the bore. With the subtend listed at 8.3" for 100 yards, I'm just trying to understand where the different poi are in using the top of the post as my aiming point with a 100 yard zero versus a 200 yards zero. Once I get led to the water trough I'll be able to drink forever - hopefully.
|
|
Quoted:
I'm shooting factory .223 55gr Hornady V-Max out of my AR and my velocity is about 2900 fps with a 16" barrel. The center of the scope is about 2.7" above the center of the bore. With the subtend listed at 8.3" for 100 yards, I'm just trying to understand where the different poi are in using the top of the post as my aiming point with a 100 yard zero versus a 200 yards zero. Once I get led to the water trough I'll be able to drink forever - hopefully. TTC |
|
Strelok+ is your friend. Get it. The basic version is free. The full version is only about $10, if I recall. Changing zero has a profound effect on the shape of the trajectory. Input your height of sight above bore, velocity, BC and other data, select your zero or the best trajectory parameters (how far from your zero you are willing to accept for your midpoint trajectory, and the software does the rest. The full version has "through the scope" reticle views that provide the exact yardage for any stadia points or subtensions in the field of view for hold overs and hold offs. It will still need to be verified and "tweaked" in the field, but should be very close. The software has over 400 scope specific reticles listed, but I do not see your Z3 3-9x36 #4A. It does list the Swarovski 4A for a Z6. You can try using that, set for second focal plane and 9x max and see if it works. Probably will.
I played with it a bit and if your reticle is like the Swaro 4A I am seeing in the program, the center post is quite short and will be only useful at extreme range with a practical zero. It is way below the center of the reticle, unlike a regular #4. What I am seeing would put the post tip out at some 600 yards for your load and a 200 yard zero. Even if I use the calculated optimal trajectory for your load (242) it is not much better. |
|
Quoted:
I'm shooting factory .223 55gr Hornady V-Max out of my AR and my velocity is about 2900 fps with a 16" barrel. The center of the scope is about 2.7" above the center of the bore. With the subtend listed at 8.3" for 100 yards, I'm just trying to understand where the different poi are in using the top of the post as my aiming point with a 100 yard zero versus a 200 yards zero. Once I get led to the water trough I'll be able to drink forever - hopefully. That should be your ~400 POA give or take with the info you provide..... With a 100 yard zero you will be -/+ 3" to 200 ...... -12.6" at 300 .... -32.1 at 400 8.3 x4 = 33.2 If you want closer than that study the links provided and fire for effect.. |
|
OP, if your reticle looks like this Swaro 4A, don't be surprised if you find out that the very low center post does not make a good holdover point at 9x and with your load corresponds to a bit over 600 yards, with any reasonable zero. This is for a 200 yard zero. Its just way, way too low to be effective.
Perhaps you should just use a good hunting zero, which would be a 50/250 approximately, and not try to shoot much beyond 300 with that scope? 
|
|
I got it! I had on old printout when I had this scope on my ML. Next to the 7.9 MOA drop column is the 237 yard marker. The inches in drop based on the 100 yard zero for 237 yards was 19.6". If I take 19.6" drop and divide by 2.37 (multiples of 100) I get 8.3" which converts to 7.9 MOA. Now I understand.
|
AR Sponsor