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Thread: scope mounting question

  1. #1
    Join Date
    Jul 2014
    Location
    Long Island NY
    Posts
    71

    scope mounting question

    Hi All,
    I'm having a problem with an Nightforce 12-42x56 on an 300 RUM/LA. mounted on Nightforce 1 pc 20MOA base/rings.
    I can't get to zero @100 yards before I run out of windage adjustment. there is no play of the base/rings when I mounted them to the action.
    this gun is my first build, Rem 700 LA, Remage Barrel from McGowen

    any thoughts on what could be going on?

    thanks
    Bill Hodkinson

  2. #2
    Join Date
    Feb 2003
    Location
    south beloit,il.
    Posts
    251

    Windage/Elevation

    Bill... I can relate to your problem and have run into the same situation... more than once......as have many others I suspect.......
    since your using high quality rings and mount...... I`ll jump to other common problems/CURES....
    first center up scope windage and trajectory knobs.....using a decent bore siter... or looking thru the bore yourself...... it shouldn't take a lot of scope adjust to put reticle on target.... if it does.......
    then call barrel mfg. and explain your problem......
    barrel bore is drilled/honed/rifled in a cured path..... usually when this happens the muzzle o.d and bore i.d. are not concentric......
    fix....... search "Barrel Clocking" on this site..... that is where the natural curveature of the bore is placed ( by machining ) in a benefical way..... mostly pointing up.....
    mount holes in receiver may not inline with centerline of bore...... common on rem. actions.
    fix.... drill out holes in receiver to 8-40...INLINE WITH BOLT/BORE CENTERLINE.....
    using burris signature rings with delrin inserts can align things,
    Hope this helps.....
    bill larson

  3. #3
    Join Date
    Aug 2005
    Posts
    798
    Remage set up - something isn't square bore to action, not to discount receiver tapped mountings holes not being in line with centerline on action as mentioned prior. seems i have heard of this before with remage set ups.

  4. #4
    Join Date
    Jul 2014
    Location
    Long Island NY
    Posts
    71
    thanks to you both, I have reached out to McGowen and I'll see what they have to say.
    Is there a way for me to see if the base mounting screws in the action are aligned?


    thanks
    Bill Hodkinson

  5. #5
    Join Date
    Feb 2003
    Location
    Sydney, Australia
    Posts
    148

    Try this

    Quote Originally Posted by Hman1956 View Post
    thanks to you both, I have reached out to McGowen and I'll see what they have to say.
    Is there a way for me to see if the base mounting screws in the action are aligned?


    thanks
    Bill Hodkinson
    Take off the scope and bases.

    Put your rifle in sandbags and bore sight it at 100 yds.

    If the base mounting screws are slot screws, screw them back in so you can sight down the slots.

    Look where they are pointing!

    Of course this wont help much if the barrel is bent like a dogs hind leg.

    Maybe you could do this with the barrel just nipped up and then loosen it a bit and see it the POI moves.

    Rob Carnell
    Sydney, Australia
    Last edited by Rob Carnell; 07-04-2017 at 02:31 AM.

  6. #6
    Join Date
    Jul 2014
    Location
    Long Island NY
    Posts
    71
    Quote Originally Posted by Rob Carnell View Post
    Take off the scope and bases.

    Put your rifle in sandbags and bore sight it at 100 yds.

    If the base mounting screws are slot screws, screw them back in so you can sight down the slots.

    Look where they are pointing!

    Of course this wont help much if the barrel is bent like a dogs hind leg.

    Maybe you could do this with the barrel just nipped up and then loosen it a bit and see it the POI moves.

    Rob Carnell
    Sydney, Australia
    Rob,
    the base is a 1 Pc. Nightforce and has zero play, I could move it if I wanted to.
    I did think about spinning the barrel 180 degrees just to see if POI moves.

    Bill Hodkinson

  7. #7
    Join Date
    Jul 2014
    Location
    Long Island NY
    Posts
    71
    so I had some time today, so a ran two straight edges next to the scope base screws and snugged them up. to see where the bore ended up.....to the left, the same way the gun shoots.
    them I spun the barrel 180 degrees and set it up again....same thing, to the left. I did also flip the straight edges and retest just to make sure they were really straight.
    see photos attachedClick image for larger version. 

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    Bill Hodkinson

  8. #8
    Join Date
    Feb 2003
    Location
    Fresno
    Posts
    5,543
    It may be that your action threads are cocked. If that is the case you can either try something with the rings using offset inserts in some of the Burris Signature tactical rings, with a suitable Picatinny base, or you can have the action blueprinted, including single pointing the threads so that they are straight and concentric. The problem with the latter approach is that you will not be able to use your current barrel, because the action threads will be too large. I have a Savage that is so far off (not sure if it is the threads or the base mounting holes) that I had to use .020 offset inserts front and rear, going opposite directions, with their parting lines vertical, the equivalent of a .040 offset in one ring. The rifle shoots fine. Others may carry on about fixing it right, but there are no unsolved problems with this approach. I actually prefer these rings for this type of rifle.

  9. #9
    Join Date
    Aug 2005
    Location
    Sydney Australia
    Posts
    82
    Bill
    Try taking out the rear screws and reassess, I had a similar situation recently and it ended up being the rear bridge "fell away" on the right hand side. So when tightened it would pull the back of the rail over to the right.
    I ended up bedding under the rear and all good.
    Matt P

  10. #10
    Join Date
    Jun 2007
    Location
    South Central WI
    Posts
    245
    Now do the same along the sides of the action body itself. That should help you narrow it down between the barrel/action interface or the scope mount holes. If it's out of wack with the action body, it's the barrel/action interface (most likely). If the barrel is in line with the action body, it is most certainly the mount screw holes I would think.

  11. #11
    Join Date
    Jan 2017
    Posts
    13
    As mentioned above, could be misalignment of barrel/action; never seen one as bad as this would need to be to account for 100% of the problem though...

    With something like this, the first- and easiest- thing to do is swap out the scope for one of known accuracy. I have an inexpensive scope that I know "works" and use it to quickly check rifles with similar complaints by boresignting as first suggested. If I can boresight the reticle into the center of the bore somewhere near center of travel I know the customer has a defective scope.

    Look at the nut/receiver face....Is there a gap showing anywhere that would indicate either an untrue surface or threads not being concentric?

    I use precision tooling from Manson to true the receiver threads to the boltway axis, and also true the contact face of the barrel nut (or replace with an aftermarket "precision" nut) . This isn't cutting them them ten thou over unless it's a custom rebarrel- but even with the same PD there's always significant thread "clean up" on factory actions (Remington or Savage).

    The NF doesn't have a large amount of windage available (total 40 minutes) but the 20 you have should be sufficient.
    You didnt mention how far off you are, left or right. With it fully cranked over, how far off POA is impact?

    If nothing is glaringly obvious with the hardware, I'd call/send it to NF for them to bench check.

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