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Need help, Sudden elevation drop at 300

 
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  #1  
Old 11-20-2013, 05:23 PM
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Join Date: Oct 2013
Location: Northeast pa.
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Need help, Sudden elevation drop at 300

Maybe you guys can ease my mind a little. Went shooting today with my dad at 300 yards, and I'm shooting a Rem. Sendero sf2 in 7mm RM. I have the gun dialed in with a good load that shoots 1/2 moa or better with Berger 180 vld and H1000. The last time we went out I was dead on with elevation and about .5 inch to the right of the bull and shot a 3/4 inch group. It was about 65 to 70 Far. with no wind and I left it there. Today it was 37 degrees Far. with a very slight wind. The group landed almost 3 inches down from the bull, a little right. I dialed in 6 clicks up and I was back up there, about an inch 1/2 group. I'm wondering if it is the scope, its a Nikon Buckmasters 6-18 that I've had for years, I know its not the best scope, but could it be the tracking, since i'm resetting for 200 yard zero when I leave the range. Or could it be that the temp. was 30 degrees cooler? I have not shot much longer range in the cold. Loads were exactly the same, And I shot some from the last time with the same p.o.i. I may bite the bullet and get a better scope, maybe a vortex. Any input would greatly be appreciated. Thanks, Mike
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Old 11-20-2013, 06:42 PM
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Re: Need help, Sudden elevation drop at 300

Although its possible some of it could be scope issues.

I would lean towards barometric pressure and temp variance if it were me. We usually try and do our load work in hunting conditions if at all possible and verify drops at average high and low temps like 35 and 70 if that makes sense. you'll definitely see a difference in point of impact.

I don't know if you keep a log book or not, but if your shooting lon range you should keep one for every rifle that way you can record the temp, baro pressure, elevation, and wind for each shooting session and the results. It is really helpful to look back after a few trips to the range and compare notes and make adjustments based on an average of your data collection. It is also very helpful to look back at where each shot landed and to use that to correct your form and or drop charts..
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  #3  
Old 11-20-2013, 07:04 PM
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Location: Northeast pa.
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Re: Need help, Sudden elevation drop at 300

Quote:
Originally Posted by 406precision View Post
Although its possible some of it could be scope issues.

I would lean towards barometric pressure and temp variance if it were me. We usually try and do our load work in hunting conditions if at all possible and verify drops at average high and low temps like 35 and 70 if that makes sense. you'll definitely see a difference in point of impact.

I don't know if you keep a log book or not, but if your shooting lon range you should keep one for every rifle that way you can record the temp, baro pressure, elevation, and wind for each shooting session and the results. It is really helpful to look back after a few trips to the range and compare notes and make adjustments based on an average of your data collection. It is also very helpful to look back at where each shot landed and to use that to correct your form and or drop charts..
Yes, that does make alot of sense.
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Old 11-20-2013, 08:57 PM
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Re: Need help, Sudden elevation drop at 300

Atmospheric conditions will change a 300 yard zero very little. Much less than 3" for your situation anyway. Parallax, lighting and or mirrage get my vote. It takes pretty severe temp/pressure changes for you poi to change by 1 MOA at 300 yards. 30-40 degrees isn't going to cause what you're seeing. Unless your ammo is hyper sensitive to temp swings causing a harmonic distortion, exterior ballistics in and of themselves are not the problem here. Since your last session and this sessions accuracy (group sizes) were very good, I doubt there is a load/barrel hypersensitivity issue here either. Caulk it up to lighting or parallax or both. It's easy to underestimate their contributions to this game.

M
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Old 11-20-2013, 09:16 PM
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Re: Need help, Sudden elevation drop at 300

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Originally Posted by Michael Eichele View Post
Atmospheric conditions will change a 300 yard zero very little. Much less than 3" for your situation anyway. Parallax, lighting and or mirrage get my vote. It takes pretty severe temp/pressure changes for you poi to change by 1 MOA at 300 yards. 30-40 degrees isn't going to cause what you're seeing. Unless your ammo is hyper sensitive to temp swings causing a harmonic distortion, exterior ballistics in and of themselves are not the problem here. Since your last session and this sessions accuracy (group sizes) were very good, I doubt there is a load/barrel hypersensitivity issue here either. Caulk it up to lighting or parallax or both. It's easy to underestimate their contributions to this game.

M
That is pretty sound advise I have seen some strange things happen do to an inversion affecting poa...but Michael is right your only looking at .25-.30 change in poa based on temp alone. I somehow read the post and then disregarded the 3" low and fixiated on the 3/4 -1 1/2 group at 300 which could be directly related to atmospheric conditions my bad!
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  #6  
Old 11-20-2013, 09:34 PM
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Re: Need help, Sudden elevation drop at 300

Good info., I appreciate the responses.
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  #7  
Old 11-20-2013, 09:55 PM
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Join Date: Oct 2013
Location: Northeast pa.
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Re: Need help, Sudden elevation drop at 300

As far as lighting, it was a little weird today at the range, bright sun out to 250, then dark and shadowed at 300. My dad even commented on it when we got there. I did notice mirage when shooting too, just wasn't as crisp. I don't know, me and dad have shot alot over the years, but I'm no expert at this long range stuff by any means. There's alot of variables involved with this, I guess that's what keeps it interesting.
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