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scope mounting

 
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  #1  
Old 09-05-2012, 11:27 PM
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Join Date: Aug 2008
Location: Sacramento, Ca
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scope mounting

GOing to put a vortex viper pst mrad on egw 20 MOA rail. Do I need to adjust for the 20 MOA. If I need to adjust my calculation came to 5.6 MIL adjusted down. Does this make any sense at all?
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  #2  
Old 09-06-2012, 05:53 AM
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Join Date: Sep 2010
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Re: scope mounting

Quote:
Originally Posted by Johnny Boy View Post
GOing to put a vortex viper pst mrad on egw 20 MOA rail. Do I need to adjust for the 20 MOA. If I need to adjust my calculation came to 5.6 MIL adjusted down. Does this make any sense at all?

im not sure what your talking about. are you talking about adjusting to sight it in?
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  #3  
Old 09-06-2012, 06:41 AM
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Join Date: Feb 2005
Posts: 564
Re: scope mounting

you just bore-sight the scope when you get it mounted... if the erector is centered from the factory (which it probably will be), then yes, you'll be dialing down some amount... but there's no point in trying to calculate what that'll be... just bore-sight and you'll get on poster board if you do it right.

I've gotten my bore-sighting technique down to where I'm able to get the first shot on an 8 1/2x11 sheet of notebook paper at 100 yards.

We had a post here a few weeks back where a guy was actually zeroing his scope before mounting it... he said he checked with Premier and got the "facts" as to how you do that.

So just bore-sight, shoot... and go from there.

Dan
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  #4  
Old 09-06-2012, 07:15 AM
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Join Date: Dec 2011
Location: S.E. Michigan
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Re: scope mounting

In essence a 20 MOA rail is a wedge. A 10 is a lesser wedge and 30 a more severe wedge and of course a no cant rail is ideally parallel to the receiver.

What a cant rail gives you is more elevation adjustment on your scope to allow you to adjust for longer range shots, if, the scope has limited elevation adjustment in the first place and adjustment for elevation has to do with physical size of the tube (why most LR scopes are 30mm main tubes or larger). If I remember correctly, a 20MOA cant rail is 0.014" difference between the extreme ends of the mounting pads (Fore and Aft).

When you buy a long range optic it's always a good idea to check the specifications and especially look at total MOA or MRAD adjustment, the larger the number, the wider range the scope has.

The Vipers are middle of the road so LR necessitates a cant rail. I have a couple. One on a 308 with no cant, one on a 338 with a 20MOA cant. Some Vipers exhibit a bad tendency and that is, they will show a crescent ring in the ocular when adjusted to the lower limits of elevation, neither of mine do, but some do. The crescent you see is actually the lower radius of the tube becoming visible in the ocular.

Just mounting a scope is less than half the process.....

Don't forget to align the rings parallel to the receiver... align the scope itself parallel to the receiver (to remove any radial cant in the crosshairs) and torque the mounts to manufacturers specification and lap the rings true with a suitable lapping bar and lapping compound. I use a machinist level to remove crosshair cant but any small bubble level will work. With the rifle in a gun cradle like a Tipton, level the gun with the bubble level crossways on the top of the rail or feceiver if flat, then place the scope and place the level crossways on the elevation turret or cap and level the scope to the firearm. That removes crosshair cant and aligns the crosshairs parallel to the receiver, very necessary with long range shots. Mounting a scope level (like the Holland) on the scope, keeps it level when shooting LR. You want the scope and rifle level at all times when shooting, A rifle canted to the side will change the POI of the bullet at extreme distance. Additionally, you might want to add an angle cosine indicator for shooting up and downhill. BTW Len Backus offers both on web store on this site.......

When you set the scope in the rings and adjust for proper eye relief (eye box), be sure to torque the rings themselves to the proper torque specification and if they are multiple fastener, progressively torque the mounting screws.

Finally, I use a dab of wicking grade threadlocker on the torqued mounting fasteners to insure they don't loosen,

Wheeler Engineering makes some good scope mounting tools including lapping and alignment bars and torque setting screwdrivers. I made my own lapping and alignment bars and actually any competent machine shop can make a set from suitable bar stock inexpensively.

Improper mounting causes the 'scope ring marks' you see referred to when someone is selling a used scope. The rings were out of alignment in relationship to the tube causing a mark on the tube when the rings were torqued down. Severe misalignment can actually cause failure of ther scope itself by twisting the tube. That causes the erector mechanism to cease to function and the scope is junk.

All rings (with the exception of the Burris insert rings) need to be lapped and even the Burris rings need alignment.

Finally, keep in mind you want the maximum ring spread spacing in relationship to the tube itself within the constraints of eye relief and rail/receiver placement as possible.

See, I just complicated the process.......
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  #5  
Old 09-06-2012, 09:54 AM
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Join Date: Aug 2008
Location: Sacramento, Ca
Posts: 25
Re: scope mounting

ok, tonight i will bore sight this bad boy and see how it goes. Thanks for all the insight to this.
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  #6  
Old 09-06-2012, 11:15 PM
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Join Date: Dec 2011
Location: S.E. Michigan
Posts: 3,457
Re: scope mounting

Something I forgot about that I remembered at work today....

Depending on the model of rifle, and if the tapped holes in the receiver are symetrical it will beehove you to ascertain which is the thicker pad on the rail and which is the tinner do you don't mount the rail backwards. The thick end goes on the rear. Not an issue with staggered mounting holes.

A 20 MOA incline would really mess up your elevation.......
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  #7  
Old 09-11-2012, 10:06 AM
Junior Member
 
Join Date: Aug 2008
Location: Sacramento, Ca
Posts: 25
Re: scope mounting

Thanks everyone for your help. I got this thing mounted and went to the range this past saturday. Took three shots to zero at 100 yards. Now that was easy.
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