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POI changing after bouncing on ATV

 
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  #8  
Old 11-18-2012, 11:43 PM
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Re: POI changing after bouncing on ATV

We've been thrashing a 338 RUM with a Sightron SIII 6-24x50 in Burris tac rings on a BEDDED EGW 20 MOA base with zero changes. It's had some hellish rides but it's in a padded case in the back of a side by side and trucks. Been dead on for almost a year now with probably 400+ rounds. The only thing that makes it shoot odd is carbon fouling. I try to give the EGW bases all the help I can, I've some of the early ones crap out but the new HD rail bedded or flat glued down hasn't been and issue.
If an optic moves zero just because it's on a 20 MOA base it's not a LR optic to begin with IMO, the most drastic movement I've seen from one of my rifles was a bedding job I did that was not stress free and would torque the action, one day it would be one place the next time move several inches and then one day it went all to hell while I was shooting and I finally found the culprit.
I would think if the scope was moving that far it would work around more when firing it, but the way those handle bar racks hold a rifle they could work over the stock I would think. Strap it down in a padded case with a bungie and take it for a ride and see if it moves then.
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  #9  
Old 11-19-2012, 09:30 AM
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Re: POI changing after bouncing on ATV

Quote:
Originally Posted by bigngreen View Post
We've been thrashing a 338 RUM with a Sightron SIII 6-24x50 in Burris tac rings on a BEDDED EGW 20 MOA base with zero changes. It's had some hellish rides but it's in a padded case in the back of a side by side and trucks. Been dead on for almost a year now with probably 400+ rounds. The only thing that makes it shoot odd is carbon fouling. I try to give the EGW bases all the help I can, I've some of the early ones crap out but the new HD rail bedded or flat glued down hasn't been and issue.
If an optic moves zero just because it's on a 20 MOA base it's not a LR optic to begin with IMO, the most drastic movement I've seen from one of my rifles was a bedding job I did that was not stress free and would torque the action, one day it would be one place the next time move several inches and then one day it went all to hell while I was shooting and I finally found the culprit.
I would think if the scope was moving that far it would work around more when firing it, but the way those handle bar racks hold a rifle they could work over the stock I would think. Strap it down in a padded case with a bungie and take it for a ride and see if it moves then.
How much downward travel do you have in your elevation turret? I only have 6 moa of down travel when sighted at 100.
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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
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  #10  
Old 11-19-2012, 09:31 AM
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Quote:
Originally Posted by D.Camilleri View Post
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.
It sounds as though the base isn't bedded. If not, I would bed the existing base first. While I'm at it, i would stick a ~.015 inch shim under the front base mount. That will get it back to 0-10 MOA bias.

I put almost no torque on the base screws during epoxy cure. I tighten the screws just enough to squeeze the epoxy. As soon as I feel resistance, I back off 1/8 turn and let the epoxy set. I'm after zero stress in the base.

What action do you have?
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  #11  
Old 11-19-2012, 09:37 AM
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Re: POI changing after bouncing on ATV

Quote:
Originally Posted by D.Camilleri View Post
How much downward travel do you have in your elevation turret? I only have 6 moa of down travel when sighted at 100.
I'll check tonight for sure but I think it was under a full rev.
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  #12  
Old 11-19-2012, 10:32 AM
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Re: POI changing after bouncing on ATV

Timely thread.

My Zeiss when zeroed at 200 is 4 clicks up from the bottom of travel. It's quite handy.

I haven't checked zero since it came back from an ATV trip where it spent plenty of time riding on the front rinky dink rifle holder. The butt was in the holder the front was resting/bouncing on the bipod.

It'll be interesting to see how it held up. Also, its not the best of bases and rings.
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  #13  
Old 11-20-2012, 08:25 PM
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Re: POI changing after bouncing on ATV

I went out and shot twice today. First time was at lunch time, first shot perfect, dialed two moa and hit 2 inches high at 100. I followed up that shot with three more and they were all an inch higher and not a very tight group. I was shooting with my bipod and a rear bag. I thought about my shooting and went back after work and performed an experiment. First, I took a piece of paper and slid it down my barrel channel and it was clear, then with the bipod mounted, I placed a slight amount of pressure on top of the scope and the paper was pinched. I removed the bipod and shot two shots at 100 with the scope zeroed at 100. Two shots touching in the bullseye. Hmmmm, time to clearance the stock in the barrel channel. I think I have found the problem. I am still going to put on the 0 cant base when it shows up so that I can at least see the bottom hash marks on the elevation turrret of the scopel
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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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  #14  
Old 11-21-2012, 02:21 AM
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Re: POI changing after bouncing on ATV

Sounds like your dial in on the issue! We just under a rev from the bottom, my buddy didn't want to check the exact number because he was afraid it would put some bad juju on it or something but it's a little more than what your at.
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