Changing POI

[moombaskier]

Have you lapped the scope rings? You could have your scope in a bit of a bind?? Ever since I started lapping all of my scope rings, regardless of caliber, I no longer experience any changes in my POI or the rifles zero. I did have a scope once that would shoot 2 groups. I realized that when I dry fired the crosshairs would jump back and forth..sometimes, but always to just two different points. That scope is now a fish wacker!

 

[westcliffe01]

Dang, a $1500+ scope and expensive rings too....

I have to say that it is not unusual for me to handle my rifle by holding the scope, particularly when taking it out the rifle case... So far I have never managed to move my zero.

This is a 30mm scope tube, right ? In my opinion, if you can deflect the scope tube with one hand, it has a structural defect, like a crack in the tube.

I only have a Vortex Viper, which is also a 30mm tube, and I always use a Warne steel one piece picatinny base and their Maxima steel rings. I'm fairly sure you could lift the average car completely off the ground with one of those if the screws were a little beefier.

I also bed the base to the receiver, since it never makes 100% contact from the factory.

I suggest you send your scope back to the factory to get checked out, since it does not seem right. It should take a lot more than what you are saying to get a 30mm tube to deflect. Even exotic alloys made for turbine blades sometimes have defects, like what we saw with the DC10 that lost the rotor due to an inclusion in the material..

 

[lisagrantb]

I haven't lapped the rings, thought about it though but I thought it was all top quality and I wouldn't need to. Tomorrow I'm going to take the scope and rings off another gun and mount it on there. I think I'm going to send the scope back anyway because it has always had a hard spot in the windage turret between 3 and 4 mills left nothing bad just a little more difficult. If that fixes it then I will put the old rings on the new scope and see if the problem comes back.

 

[X-man]

Something is strange here.
You can take a one piece scope (with a tube thickness 3 times that of Leupold's) that is bolted to a substantial scope base and more substantial action and can cause a 1.5 MOA shift? That is not possible!

Even if the scope internals were totally fubared there is no way you are going to deflect that scope with light hand pressure...unless the scope base or rings are wrong.

A hard spot in the tracking is symptomatic of misaligned rings.
What are you running for rings and bases?
Got any pictures?

 

[lisagrantb]

It has Seekins base and rings, I bedded the base with Devcote but didn't lap the rings. When I got this scope about 1.5 years ago it had a hard spot right out of the box. I talked to NF and they said send it back for repair but it would take a few months to return it so I have been putting it off because it didn't seem to affect anything and I needed to use the scope.

 

[MudRunner2005]

Gee......I believe we've come full-circle here, like my original post. Something is either wrong or loose in your scope mounting or something is wrong with the scope. There are only 2 options....Lap your rings and try it again, or lap your rings and send your scope back to NF to have them repair what is wrong.

Not that there haven't ever been, but I've never heard of a NF having turret issues and making it to the consumer...

 

[lisagrantb]

Last night I completely dismantled the gun, base and stock. I re bedded the base (didn't find anything wrong with the old bedding) and put just the barreled receiver in the vise. I took a dial indicator and mounted it to the barrel about 3 inches from the receiver and put the indicator on the rail. I could put pressure on the tang and the indicator would move .001" in each direction and always come back to zero, I would think this would be normal flex in a receiver especially one not in a stock for extra support. I then mounted the original scope and rings. I moved the indicator still mounted to the barrel to read on the front ring cap, I could see the +- .001 movement but this time it would not go completely back to zero. It wasn't much off only about .0002 (the best I could tell) I don't know if that is enough to worry about. I then moved the indicator to the top of the objective bell and repeated the test. This time I was getting a change in zero of about +- .001" that is a .002 error. I ran a quick calculation and that .002" on a 4" ring spacing would give me a little over 1MOA change. My next test will be changing out rings and scope to see what changes that makes.

 

[X-man]

Hmmm... this reminds me of an issue I had with a custom built 50BMG rifle.
Good accuracy yet POI shifted around.

$2000.00 in components later I figured out that the gunsmith effed up the threads on the barrel...I could actually unscrew the barrel by hand!

Flip the receiver upside down and try your test again. I can only think of one place you can get play from...That is exactly how I resolved my BMG issue....If I am right you are getting a bigger reading off the scope because it is farther from the threads and shows the movement more.

Might be time to take your rifle in to a 'smith.

 

[lisagrantb]

So you are saying it could be loose or incorrect threading on the barrel not allowing it to mate properly with the receiver and this can cause the movement when I put pressure on it. Hmmm something to check out.

What exactly do you mean when you said flip the receiver upside down and try it again.

 

[X-man]

So you are saying it could be loose or incorrect threading on the barrel not allowing it to mate properly with the receiver and this can cause the movement when I put pressure on it. Hmmm something to check out.

What exactly do you mean when you said flip the receiver upside down and try it again.

See if you can get the receiver to move the opposite way or get it to move both ways to see if you can double your reading.
maybe clamp the barrel at the shank near the action and try to measure any action movement both ways.
I'm no gunsmith and am just guessing here.

 

[lisagrantb]

Ok, after much testing here is what I have found out.

The equipment used for the test was a Remington 700 bluprented and Brux barrel with Nightforce rail the second gun is a Defiance action with a Lilja barrel and Seekins rail, 3 scopes, 2 Nightforce scopes one with Seekins rings the other with Nightforce rings and 1 Lupy MK4 with Badger rings. I removed the stcks from both guns and checked and torqued everything. I then took the 700 and clamped it in a barrel vise and mounted and torqued the first scope on it. I put the crosshairs on a 100 yard target and applied upward and downward pressure on the objective bell checking the movement after each time ( actually the sunshade so that gave a little more leverage) not a lot of pressure but firm. I watched as the scope would move its POA about .4" up and down. I repeated this with all 3 scopes on the first rifle and the results were all the same, so i'm thinging GUN right. Then I switched guns out and tested all 3 scopes on the Defiance and guess what, same POA change with all 3 scopes on the second gun. Now I'm saying SOB whats up now. I then took all 3 scopes (one at a time) with the rings mounted and clamped the rings in the vise of a milling machine, only the scope and rings nothing else. this setup is as stable as I can get. I pushed, pulled, twisted and yanked on the rings and turret trying to see any movement. The setup was rock solid I couldn't see any movement of the crosshair on the 100 yard target. I then took my hand and applied pressure to the objective bell and guess what, the crosshair would move up and down depending on the direction I pushed the bell (I would expect that because I'm flexing the tube) but they wouldn't go back to zero after I released the pressure, there was a .4" **** in POA the same that I was seeing when the scope was mounted on the gun. I repeated this with all 3 scopes and the results were just about the same for each scope. I think the tube is flexing and moving the internals and they aren't returning back to the same point, i'm sure the tube returns back. I dont think something is broken with all 3 scopes I think its a design limitation and just something to be aware of. Any thoughts on this, it would be nice if someone could try the same thing and confirm or disprove what I found.

 

[Broz]

Put another scope on the rifle.

I agree, but during the process I would remove all the mounts looking for even the slightest movement. It could easily be the mounting system, (bases or rings)

What are they?

Jeff

EDIT; we were posting at the same time. What you are seeing I find as normal. I have preached about spending the money for good one piece rails so recoil is not transferred into a scope tube. A good rail epoxy bedded to a receiver will strengthen the action and allow things to stay true. I say use a good one piece rail, bed it to the receiver using a straight edge to assure it is true, and mount it in rings of high quality that are on plane to each other. Then torque it all down as a whole. It does make a difference, but only a difference that few will ever realize.

Jeff

 

[lisagrantb]

I did change the scope, 3 scopes on 2 different guns all combinations. The rings were mounted on the scopes and I clamped the rings in a vise that is mounted to a milling machine I don't think you can get any more solid than that and the problem was still there with all 3 scopes. The rings are Nightforce, Seekins and Badger I wouldn't think that all 3 rings would allow the movement. I really think it's the scope internals and the way there designed that cause the error, just something to be aware of that could affect your POI.

 

[Broz]

I did change the scope, 3 scopes on 2 different guns all combinations. The rings were mounted on the scopes and I clamped the rings in a vise that is mounted to a milling machine I don't think you can get any more solid than that and the problem was still there. The rings are Nightforce, Seekins and Badger I wouldn't think that all 3 rings would allow the movement. I really think it's the scope internals and the way there designed that cause the error, just something to be aware of that could affect your POI.

I am agreeing with you. And offering why a stable mount is important to reduce this all we can. I also like the rings as far apart as possible. Also why I never use my hand on top of a scope during a shot to steady the rifle.

Jeff