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POI changing after bouncing on ATV

 
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  #1  
Old 11-18-2012, 08:50 PM
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Location: Worland, Wyoming
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POI changing after bouncing on ATV

I have recently been seeing a change in point of impact on my 338 rum after bouncing around on the handle bar rack on my ATV. I have a Sightron S-III 8-32-56 with burris tactical rings and an egw heavy duty 20 moa picatinny rail. After bouncing around on some rough two tracks antelope hunting, my POI moved up 3 inches and right 7 inches at 100 yards. I found this out after two bad hits on antelope. When I got home, I removed the scope and checked my base mounting screws, all tight. I remounted the scope, went back to the range and resighted my gun. I had to move the scope down 3 MOA and Left 7 MOA. When I was done, it grouped perfect.

My big question is: Should I trade out my 20 MOA base for a 0 MOA Base so that the scope adjustment will be more centered in the tube? Currently I only have about 6 MOA of down travel in my up down adjustment. The S-III has 100 MOA of adjustment, so I really don't need the 20 MOA base to get to my max distance of around 1300 yards. Could having the adjustment be so close to bottoming out comprimise the integrity of the adjustments? The tracking of this scope has been very good, but I went out to the range to double check the zero and I found that I was shooting 3 inches high again. This was after bouncing around on the ATV again and would explain why I over shot a muley a couple weeks ago.
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Remington model 700 300 RUM LH 26" rem ss/blued receiver lam stock 215 Berger @3025/180 NAB @3300
Remington model 700 338 RUM LH 27" Broughton 5C 225NAB@3300 /300gr Berger@2830
Savage LH 22-250
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  #2  
Old 11-18-2012, 10:01 PM
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That seems like a lot of POA shift. 3-7 MOA is huge. The scope installation sounds solid. Sightron scopes have a better reputation than that. I would not invest in a 0 bias base - seems unlikely that the problem is too much elevation adjustment.

Are you sure the turret knobs are not rotating? I'm also wondering if you have a stock issue.
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  #3  
Old 11-18-2012, 10:25 PM
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Re: POI changing after bouncing on ATV

I have seen more than a few of the EGW bases fail in a few different ways. The last two were moving on large caliber rifles with heavy scopes. I would pull it and inspect for egged holes or wear signs from it moving.

Jeff
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  #4  
Old 11-18-2012, 10:44 PM
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Re: POI changing after bouncing on ATV

The base moving was my first thought, and that is why I removed the scope and checked the screws. They were all tight when checked with my torque wrench. I also looked for marks to show if the base had moved and couldn't see any. The POI hasn't changed at all from just shooting, but it has changed twice in as many atv trips and it makes me wonder if the pressures on the crosshairs aren't even with the turret being so close to the bottom of the range. I verified the adjustment on sightrons website and this scope is supposed to have 70 moa of elevation not 100 like I thought. I emailed sightrons customer service to see what they have to say about this condition. In the past when I have contacted them, they like to see the turrets starting close to the center of travel. I guess I will see what they say.
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Remington model 700 300 RUM LH 26" rem ss/blued receiver lam stock 215 Berger @3025/180 NAB @3300
Remington model 700 338 RUM LH 27" Broughton 5C 225NAB@3300 /300gr Berger@2830
Savage LH 22-250
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  #5  
Old 11-18-2012, 10:47 PM
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Location: Worland, Wyoming
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Re: POI changing after bouncing on ATV

Quote:
Originally Posted by bruce_ventura View Post
That seems like a lot of POA shift. 3-7 MOA is huge. The scope installation sounds solid. Sightron scopes have a better reputation than that. I would not invest in a 0 bias base - seems unlikely that the problem is too much elevation adjustment.

Are you sure the turret knobs are not rotating? I'm also wondering if you have a stock issue.
My stock is a Bell and Carlson Alaskan with full length pillar bedding, the barrel is fully free floated. My turrets are all set to 0 at 100 yards and I usually hunt with the elevation set to 3 moa which puts me dead on at 300 and then I dial from there.
__________________
Remington model 700 300 RUM LH 26" rem ss/blued receiver lam stock 215 Berger @3025/180 NAB @3300
Remington model 700 338 RUM LH 27" Broughton 5C 225NAB@3300 /300gr Berger@2830
Savage LH 22-250
Reply With Quote
  #6  
Old 11-18-2012, 10:53 PM
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Join Date: Jul 2004
Location: Texas
Posts: 5,444
Re: POI changing after bouncing on ATV

Quote:
Originally Posted by D.Camilleri View Post
I have recently been seeing a change in point of impact on my 338 rum after bouncing around on the handle bar rack on my ATV. I have a Sightron S-III 8-32-56 with burris tactical rings and an egw heavy duty 20 moa picatinny rail. After bouncing around on some rough two tracks antelope hunting, my POI moved up 3 inches and right 7 inches at 100 yards. I found this out after two bad hits on antelope. When I got home, I removed the scope and checked my base mounting screws, all tight. I remounted the scope, went back to the range and resighted my gun. I had to move the scope down 3 MOA and Left 7 MOA. When I was done, it grouped perfect.

My big question is: Should I trade out my 20 MOA base for a 0 MOA Base so that the scope adjustment will be more centered in the tube? Currently I only have about 6 MOA of down travel in my up down adjustment. The S-III has 100 MOA of adjustment, so I really don't need the 20 MOA base to get to my max distance of around 1300 yards. Could having the adjustment be so close to bottoming out comprimise the integrity of the adjustments? The tracking of this scope has been very good, but I went out to the range to double check the zero and I found that I was shooting 3 inches high again. This was after bouncing around on the ATV again and would explain why I over shot a muley a couple weeks ago.


In my opinion 20 moa bases are to much for the distance you intend to shoot. a 5 MOA or at most
a 10 MOA should keep you close to center of the adjustments,

When you get to the extreme limit of the retical adjustments problems are common.

I like to site the rifle in at 100 or 200 yards, look at the ballistic table for your load and then, using the drop chart look at the elevation required to hit center target at 1000 yards (Or your target distance) and add a MOA base with the same (Or close) MOA . This will help keep the scope close to center.

This should keep you within the scopes range of adjustments.

This may solve your problem.

J E CUSTOM
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  #7  
Old 11-18-2012, 11:35 PM
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Join Date: Jun 2004
Location: Worland, Wyoming
Posts: 569
Re: POI changing after bouncing on ATV

This is why I am thinking of going back to a 0 moa base. I am only 6 moa from being bottomed out on elevation with the 20 moa base. With a 0 base, that should put me at 26 moa which gives me a max of 44 moa up. At 600 yards, I am only dialing up 10.4 moa which would put me right close to the middle of travel. I can't remember off hand how much elevation I need for 1250, but I think it was around 30 moa which should still be fine.
__________________
Remington model 700 300 RUM LH 26" rem ss/blued receiver lam stock 215 Berger @3025/180 NAB @3300
Remington model 700 338 RUM LH 27" Broughton 5C 225NAB@3300 /300gr Berger@2830
Savage LH 22-250
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