Rifle Scopes Nikon M308 "problem"

[bluto77]

I just mounted one of the Nikon M308's to my AR-10. Took it to the range today, and I have the elevation dialed in perfectly. The "problem" (that's in quotation marks because I have a feeling this is a stupid question) is when I was trying to get it centered. The rifle is shooting abou 5" to the left. I have dialed the turrets as far to the right as they can go, yet I'm still about 5" to the left. At some point it stopped moving, yet I could still keep dialing. At another point I actually had unscrewed the dial. As of now I'm stuck. I can't dial it over any further. I think the answer to this is to take the scope off, "zero" it, and then remount. Not sure though. All answers welcome, even the barrage of smart-ass ones I know are sure to come. The good news is, my rifle was shooting great MOA and less groups!

ETA: I'm using the mount that came with the scope from Nikon.

 

[bluto77]

Re: Nikon M308 "problem"

I may not be asking the right question. What term/phrase would I call this "problem" so I can do a search on it?

 

[ORD]

Re: Nikon M308 "problem"

It could be any number of issues, but here are a few random thoughts followed by my suggestion to you:

1) mount is crooked/out-of-spec;

2) upper receiver is out-of-spec;

3) could be a problem with your rifle itself (not likely as you say it is grouping well aside from your scope not being able to obtain zero); and/or

4) your scope $#!T the bed and needs replaced/fixed (this would be where I'd put my money. Your scope has only about 20MOA of adjustment for windage in either direction...40MOA total...from its mechanical zero. Depending on how much elevation you used for zeroing, you actually won't have even that full amount available, but if you've used up all of what you did have left and still need roughly another 5MOA to get zeroed, there's a pretty significant problem. Contact Nikon CS for an RMA/warranty repair cert to send it back, along with the mount, for inspection/repair).

A good first step before going back to Nikon is removing the scope/mount from the rifle and the scope from the mount and starting over with your entire mounting/zeroing process. Return the scope to the middle of its adjustment range for both windage and elevation (mechanical zero). Inspect your mount and be sure that it is clean and free from any burrs or debris that could be causing it to mount crooked on your receiver (check the base of the mount, as well as the clamping plate, screws, etc.). Check your receiver for any signs of unusual wear/tear/damage to the areas where you mounted the scope mount. Mount everything back up and torque it all down per the mfg's specifications, bore-sight it, and then try to zero it again on the range.

 

[rcmigpilot]

Re: Nikon M308 "problem"

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bluto77</div><div class="ubbcode-body">
ETA: I'm using the mount that came with the scope from Nikon. </div></div>

Try spinning the mounting base (the part with the through bolts that attaches the ring assembly to the top of the receiver) 180 degrees. I had the exact same problem using the Nikon mount on my AR.

 

[bhoges]

Re: Nikon M308 "problem"

I had the same exact issue with a rifle I worked on for a friend. With the same scope and mount. If your not careful the mount can be installed slightly off making it almost impossible to zero. Return the scope to mechanical zero and torque all the mount screws evenly. Perhaps tighten the middle first.

 

[bman940]

Re: Nikon M308 "problem"

Bluto, I'm going with Brian and part of what ORD did so well to describe. Make sure screws are torued evenly to prevent misalingment of mount. While I have mounted dozen's of M-223 Mounts which are very similar I have only had an issue similar to yours one time and that was when someone else did the mount. We reattached the mount using a torque wrench and tighted everything to 20 ft/lb I believe. Returned scope to mechanical zero and started over. 5 shots we were done after going thru a box previously. Sometimes just another set of eyes or in this case, a second or third or I am sure to come a 4th,5th opinion is nice. Please keep me in the loop on how this works out for you. I have heard nothing but good things about this scope from those that have received theirs, hopefully I'll get my hands one one sooner then later.

 

[bluto77]

Re: Nikon M308 "problem"

Thanks for the suggestions. I re-mounted the one piece scope ring on the picatinny rail and re-mounted the scope after returning it to mechanical zero over the weekend. Hopefully I can get back out to the range this week or this weekend and see if that did the trick. I made sure to tighten the middle screw of the three on the one piece ring first, then the back and front evenly. Tightened all of the screws on the actual rings gradually/at the same time. I'll be sure to post the results from the range.

The rifle is a Larue PredatAR 7.62, so if the issue is related to the rifle instead of the scope I'm going to be pretty pissed off. That's by far the most expensive firearm I've ever purchased. I almost feel guilty putting the Nikon M308 on it instead "higher end" glass, but there wasn't much left in the budget after buying the rifle.

 

[bhoges]

Re: Nikon M308 "problem"

You'll be fine the scope works just fine. Bring an allen key to the range in case you need to adjust it there. Good luck sounds like a great setup.

 

[Dan Newberry]

Back from the dead thread... but we did run into this issue with this Nikon mount on a customer's rifle over the weekend. We found that the mount will actually pivot as it sits on top of the picatinny rail, depending on whether you tighten the front screw more, or the back screw more... torquing them evenly did not solve the problem... it ended up being a bit of guessing game... the scope was pointing to the right, causing shots to be way off to the left.

We centered the scope for windage, then mechanically adjusted the windage by drifting the base itself in the following manner:

1. loosen all three screws to light snug...
2. tighten rear screw about 1/4 turn *more* than the front screw, then evenly tighten both the front and rear screws. This gave the rear screw an extra 1/4 turn when both screws were tight. This basically pointed the scope back in the direction it needed to go.
3. tighten center screw last.
4. test rifle. in our case, it needed more... trial and error... but finally we got the thing windage centered.

The mount works, and is solid. But it was a lot of trouble to make it right. Nikon really needs to address this...

Dan

 

[bhoges]

I agree you can have an issue getting it to stay on straight. I have several of those mounts and never really had any problems. At the same time Ive worked on two rifles that used up all adjustment to get zeroed. Seems the windage is alway the problem. Warne makes those mounts.