Zeroing/Elevation Change

blackops · May 1, 2015

Hey fellas,

I zero my rifle in around 400ft. I hunt around 10,000 ft. Will my zero change at the greater altitude or can I just zero at 400ft and have my custom turret made around my ballistics and 10,000ft? I understand the pressure change, but I'm going to get my CDS turret made and I want to be absolute certain of what I'm doing here. Another thing is I hunt at 400ft sometimes as well. Should I have two turrets made for the different altitudes or meet them half way? I'm looking to get the best possible accuracy so I'm think two different turrets.

Appreciate the help.

TTundra · May 1, 2015

I'll shoot from 600 ft elevation to 5000 elevation, never really see to much of a change based solely off elevation, maybe ~1'' with a 300 win shooting 180 nosler partitions. Its really pressure differences that can throw a wrench into the works.

Custom dials are made this way, they pull that data when manufacturing them for your load and specs. Never hurts to shoot a few to check zero before your hunt at the peramiters you will be hunting in.

taliv · May 1, 2015

guess that depends on what 'best possible accuracy' means to you on a hunting rifle you'd carry around the mountains. i go from zero to 5000' ASL without a zero shift. if i was going from zero to 10,000 i'd for sure confirm my zero before shooting at big game. but i would expect it to be within an inch at 100 yards.

as for the turrets, it depends on what distance you are shooting. i'd use JBM online to model it. you will likely see past 500 yards, that every few thousand feet makes a tenth mil difference or so. 10000 is quite a lot and if you plan to shoot 500 yards, i would definitely get multiple turrets.

HOWEVER, you need to understand that it is the density altitude that is important, not the actual distance above sea level. for example, the farm i usually shoot on is actually 1100' above sea level but in the winter, the DA is -500' to -1000' and in the summer the DA is 2000' to 3500'. I'm going to colorado in 3 weeks to shoot the snipershide cup. The range is just under 5000' above sea level, but given the expected temperatures, I'm making dope cards for 6500' to 9000'.

tuj · May 1, 2015

confirm your zero if possible. Air density indeed can affect your zero.

blackops · May 4, 2015

I guess I'm going to have to go up way before hunting season and zero my rifle.

Vern Humphrey · May 4, 2015

While air density can affect zero, I zeroed my .35 Brown-Whelen and my pre-64 M70 Winchester at just about sea level when I lived in Tidewater Virginia, drove to Eagle County Colorado, verified my zero on a range there at around 8,000 feet -- and didn't have to touch the knobs on either rifle. I killed elk at around 11,000 feet with no problems at all.

blackops · May 4, 2015

Thanks Vern. That make me feel a little better.

gamestalker · May 5, 2015

Elevation has enough of a significant difference in external ballistics that I always zero my rifles in at the elevation I'll be hunting at.

I first noticed this years ago when I was hunting antelope at 7,000'. I shot the rifle at 2,000' elevation, my rifle was shooting very noticeably lower poi then @ 7000'. At 500 yds, poi was about 3-4 inches lower than it was at 7000's. So wondering what was going on, I decided to run some rounds across the chrony @ 200 yds. at both elevations. I don't remember the exact numbers, but it was definitely a significant negative impact at the lower elevation. The projectiles maintained a higher velocity when fired at higher elevation. Thinner atmosphere equates to high BC, less drag.

GS

blackops · May 5, 2015

Thanks gamestalker. Point taken.

Zeroing/Elevation Change

blackops

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TTundra

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taliv

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tuj

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blackops

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Vern Humphrey

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blackops

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gamestalker

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