September 23, 2010
Scope mounting mistakes can cost you. Here's how to do it right.
Most scope mounting work is straightforward, but even experienced shooters bungle mounting jobs. Not long ago, in a hurry to scope a rifle, I installed the rings without checking height. I'd assumed the front and the rear rings were the same; alas, they were not.
Then, as if to add insult, I botched a second mount job when I didn't realize the base screws were a few threads too long and were bottoming out. Result: I sheared off both screws in the receiver.
And once on an African hunt with a borrowed rifle, the gun's Redfield-style scope base lost its left-hand windage screw. I should've checked the rifle when some shots flew true and some did not, but I didn't. Unfortunately, it cost me some animals.
To prevent these and other problems, attach your scope when you have time to think about what you're doing, where you have good light and no distractions. Like taking an important test, shooting a rifle match or giving a speech, affixing a scope to your rifle is best done early in the day, when you're not tired.
Here's how to do it. Snug the rifle in a rifle cradle. If you don't have a cradle, get one.
Swab the receiver and mount or ring bases with gun-cleaning solvent to remove grease, grit and fingerprints. Follow with a dry cloth, then a silicone-impregnated rag.
Put base screws in a coffee saucer. If you don't, you'll lose one or more. Guaranteed.
Set the base on the receiver and start the screws using a close-fitting magnetic screwdriver tip--the tip only. After screws are seated, add the screwdriver handle and snug them alternately. Check bolt clearance by cycling the action before tightening the screws. If you feel any undue resistance, back off the offending screw and replace with a shorter one or grind to fit.
Before attaching rings or giving base screws a final turn, set your scope on the base to check ring spacing and ensure that you'll get proper eye relief. Variable scopes with short sections of free tube can limit your options. Some scope bases can be reversed to your benefit.
If you don't see how you can place the scope where you want it, consider another base or extension rings. While rail-type bases aren't trim, they typically offer more latitude in sight placement.
Tighten the base screws as if you were paid by the inch-pound but will be docked a month's wages if you twist one off. Loc-Tite is not necessary, in my view. If you wish to lock those threads, use blue Loc-Tite; it allows screw removal more readily than the red version.
Leave Ruger-style rings snug but not tight to the receiver so the scope can self-center.
Separate the rings, using the saucer to hold ring screws. Keep the ring halves paired and the ring ends oriented as they came from the package. CNC machining is supposed to make such matching unnecessary, but it's still a good idea.
Depending on mount design, you'll first affix rings to base or clamp them lightly to the scope tube. Run the ring screws in finger-tight. If the rings are vertically split, heed directions as to the tightening sequence of all screws. You'll want a gap in both ring junctures when the scope is secured. It doesn't matter whether the split is vertical or horizontal; don't let ring halves contact each other.
While the scope is still loose in the rings but the lower ring or ring juncture solidly affixed to the scope base or rifle, slide the scope forward until you get proper eye relief.
Check eye relief prone and sitting, not just offhand. Wear heavy clothes as well as light. Scope position will be a compromise, but you'll want the eyepiece to clear your brow during recoil every time.
Most hunters place the scope too far back for prone or uphill shots, and the ocular ring prints a half-moon between their eyes.
As a rule of thumb, I start with the ocular lens directly over the rear guard screw--after adjusting the focusing ring for a sharp reticle image. Then I mark ring position on the tube with a pencil. It's best to leave 1/8 inch between rings and any junctures in the scope tube.
Next, turn the scope until the vertical reticle wire is lined up with your rifle's buttplate. Use a square or vertical edge or Wheeler Engineering's Level Level Level to check. If the reticle is not plumb, you will cant the rifle and miss at extended range.
Snug ring screws alternately, as you'd tighten lug nuts when changing a tire. Before finishing, see that the gaps between ring halves appear equal. These screws needn't be as tight as base screws. Over-tightening can mar and even deform a scope tube.
Bore-sight the rifle. If your mount base allows you to adjust ring position for windage, run the scope's windage dial to its center position (count clicks from one stop to the other, then come back half that number) and bore-sight using the base screws. That way, you'll keep as much windage adjustment as possible and maintain the erector assembly in the middle of the tube.
Once you've bore-sighted, it's off to the range to get your desired zero.
A careful mounting job should give you confidence in your scope. Honestly, it's rare that modern scope mounts are "knocked off" by incidental bumps in transit or on the trail.
While you're smart to check zero in camp after extended travel, you shouldn't find any change. Just remember to fire a three-shot group before pulling turret caps and fiddling with the zero.