Numbers don't add up

danblkelk

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Jul 9, 2014
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I only have a 100 yard spot to shoot. I have an Idaho elk hunt in october where the ranges are 400 + yards. I put a target at the bottom of a tall cardboard target. Using my Vortex Razor's internal bullet drop comp. I checked zero on my 300 Win Mag using 180 gr. Federal Trophy Bonded tip factory. My zero was 2' high at 100. Now using the scopes 300, 400, and 500 yard marks I aimed at my zero spot and shot at the yardage mentioned above. My 300 yard mark was right on at 6.5 inches of holdover. The 400 yard was 14.7 inches high vs Federals 19.2 inch,
THe 500 yard was for me 22.5 inches vs Federal's 38.6 inches. The Federal info came from the ballistic calculator. My rifle can't be shooting that flat so can someone explain where I went wrong
 

26Reload

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What i did was to shoot a distinct distance..in this case 450yards...matched it to my bottom post and when the buck showed..down he went......
So your shooting distance lines should match up at a specific selected power setting....otherwise at lowest power your gradient will be really long..and full power it will be much shorter.....
Maybe start in reverse...figure out your 500yd...then work down at same power....
 

Bravo 4

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Figure out what the distance between stadia lines is at 100, then match it to your drops on with a ballistic app. It probably won’t be a 100/50/25 yard distance (something like 316 instead of 300 even), but at least you will know. I’m gonna say that if you are just guessing you are setting yourself (and potential game) up for failure, the further the distance the more potential error. Even if you think it’s lined up at 100, you need to check when you get to your destination. Going up in altitude and such will throw things off.
 

lancetkenyon

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If it is a BDC reticle, subtensions are actually something like 0, 1.5MOA, 4.5MOA. 7.5MOA, 11MOA IIRC. (for Vortex)

Not many rifles are going to produce exactly those drops to hit 300, 400, 500, 600 yards perfectly with a 200 yard zero.

For a quick reference, the 180 Federal @ 3000fps, 6000' elevation @ 40* F will drop something like:
1.9 MOA @ 300 (6.0") (1.5MOA subtension is 4.7" @ 300) Close enough
4.2 MOA @ 400 (17.5") (4.5MOA subtension is 18.8" @ 400) CLOSE
6.7 MOA @ 500 (35.2") (7.5MOA subtension is 39.25" @ 500) 4" high, probably close enough on a bull elk, but close to the top of the lungs
9.5MOA @ 600 (60") (11MOA subtension is 69.1" @ 600) 9" high @ 600 is probably either a miss or a wounded bull
 
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memtb

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I am blessed with a 300 yard range which made it easy to get my scopes with the “hash marks” for varying ranges. I merely used my 300 yard line in the scope and zero’d that line at 300. You could do similar, using your 100 yard range...though, you will have some error!

If you know the BC for your bullet, and can chronograph your velocities, developed a drop chart, using these factors. Determine how many inches high at 100 yards you would be, using your 300 yard “hash - mark” for 100 yard shots. Then using your 300 yard “hash - mark” at 100 yards, and adjust your group to be low (x number of inches) at 100 yards. This should get you close at 100 yards, using your primary cross hair! Theoretically your 300 should be “spot on”! You just have to be willing to accept some error at.....100, 200, 400, etc.

I’ve done this using a similar scope system. I zero at 300 yards with the 300 yard “hash-mark”.....and accept the fact I will not be perfect at other ranges. This may not work flawlessly for prairie dogs ....but, should work for big game!

I hope that this was understandable! It’s a rather confusing way to get you on target at longer ranges.....using your 100 yard range with the “hash- marks” built into your scope! memtb
 

danblkelk

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Yes it groups 2' high at aoo yards. I did shoot only 2 shots as I when up in distance because I was short on ammo.
The scope was set at 9 power (it goes to 10) >IF it makes a difference I have the german #4 recticle
Thank you Brovo 4 for that idea. I will download the app right now.
Thanks guys.
 

lancetkenyon

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Yes it groups 2' high at aoo yards. I did shoot only 2 shots as I when up in distance because I was short on ammo.
The scope was set at 9 power (it goes to 10) >IF it makes a difference I have the german #4 recticle
Thank you Brovo 4 for that idea. I will download the app right now.
Thanks guys.
2' or 2"? I bet 2".

But seriously, if you have a SFP scope w. BDC reticle, on 9X, your subtensions are not correct either. A SFP Vortex Razor
Too many errors in your theory to even try and tell you what is going on.
2" high @ 100 is not a 200 yard zero. More like 245ish yards.
Your subtensions in your BDC are more than they should be. Like 20%. 10x would be accurate, 5x would double their value to 0, 3, 9, 15, 22MOA respectively. Your subtensions in your BDC reticle are actually like 0, 1.8MOA, 5.4MOA, 9MOA, and 13.1MOA @ 9X.

Unless you have the new Vortex Razor Gen III 1-10×24 FFP. Then forget all the math I just threw your way.
 

waspocrew

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The scope was set at 9 power (it goes to 10) >IF it makes a difference I have the german #4 recticle
I'm assuming this is a second focal plane scope - in this case, the subtensions (or measurements for the BDC lines) apply to MAX power (10x for your scope). Like others have mentioned, they really are only to try to "ball park" your shot and rarely match up perfectly. Trying to use them at a lower power will cause issues.
 

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