When a rifle is hitting all around the spot you are aiming at, the first reaction of many is to blame the scope. I saw that a lot when I was gunsmithing, but even back then the blame rarely fell on the scope. It was usually the mounting process that was at fault. Poorly mounted to your rifle, even the best scope will dash your expectations.
I rediscovered this last summer when a fellow shooter and I were attempting to zero a .338 Lapua. We were firing on a steel plate at 500 yards - a chip shot for this caliber - and I put four shots into a group the size of my fist; the fifth shot went over the right corner of the plate. From behind the spotting scope, my buddy told me the rifle had done a similar thing to him, albeit the flyer going low and left. We later found out the base was loose.
How can you avoid a similar predicament? Simple. Pay attention to the details. There are three potential locations for problems: the base-to-receiver attachment, the rings-to-base attachment and the ring assembly itself. Some designs, like Talley rings, will have only the base-and-ring attachment to focus on since the rings clamp the scope and secure to the base with the same operation and same set of screws.
The first process I developed as a gunsmith was simple. I'd unwrap the parts, make sure the parts count was right, tighten them all on as tight as humanly possible, and go sight it in. But over time I learned there was a lot more to the process. Here are my recommendations.
First, collect the parts and tools. You'll obviously need the rifle, scope, base and rings. You'll also need a bottoming tap of the right size, usually 6-48, but some rifles now come tapped 8-40. You'll need the proper-size Allen wrenches, Torx wrench or a screwdriver that fits properly, a degreasing aerosol, a straight edge and alignment rods.
A torque wrench is handy, but not an absolute must. If you have one, great. If not, Weaver makes one that is not only compact, but also inexpensive.
A collimator is also a nice addition, but if you have a good view out a window, you can make do with a distant object.
If you are dealing with a particularly heavy-recoiling cartridge, you may want to use a ring-lapping bar, and as a last detail, you may want some Loctite.
I was never a fan of Loctite in scope mounting, but I can see where some would be, and so I'll cover that at the end.
Doing a scope-mounting job in your lap is a good way to hurt yourself, to do damage to the rifle or to the scope, or some combination of all three. I'm going to approach this from a bolt-action perspective, so remove the bolt. Remove the plug screws from the receiver.
Hand-check the fit of the base or bases on the receiver. If you're using a one-piece, check to make sure it fits without wobbling. A wobbly fit is bad, and you need to find out why it wobbles. Fixing it could be as simple as you've got the wrong base, but it could also be a miscut, over-polished or out-of-spec base or receiver. If it's the receiver, you're now into advanced gunsmithing corrections—and well beyond the process we're covering.
If you have a two-piece base, use the supplied Allen wrench or screwdriver to lighdy install the bases. Use your straight edge to check that the front and rear are level. Check both the tops, to make sure they are level, and the sides, to make sure they are aligned.
Again, if they are not, recheck to make sure you have the correct ones. If you do and they are not level, you again have an advanced problem, beyond the scope of this article.
Take the base or bases off the receiver. Spritz a shot of degreaser into each of the receiver screw holes for the base or bases. Use the bottoming tap to clean the threads out. Reach into the receiver with a fingertip and wipe out the grit and crud the tap pushes ahead of it, crud that would otherwise be inside your receiver.
Place the base or bases on the receiver and hand-tighten the screws in place. No need to do more than snug them down. Use the straight edge again, and this time also check the bolt for fit. There are a number of rifles and scope base designs that use screws of differing lengths. If you put the long screw in the short hole, you could have a screw sticking into the path of the bolt. You want to find that out sooner rather than later.
I asked a few of the makers of scope-mounting hardware about torque limits. All these measurements are inch-pounds, not foot-pounds, and you can't use a "light touch" with a torque wrench calibrated to foot-pounds and do anything but mess up a scope installation.
Now it's time to torque the base screws. In the interests of finding out just how.
Weaver recommends tightening the base screws to 20 in.-lbs., and Talley recommends 25 in.-lbs. Leupold is quite specific. For 6-48 base screws it recommends 22 in.-lbs. in a steel receiver and 12 to 14 in.-lbs. in an aluminum receiver. If your rifle uses 8-40 base screws, Leupold suggests you set your torque wrench to 28 in.-lbs.
If you have an inch-pound torque wrench, go for it. If not, these are limits that anyone with normal hand strength can easily generate. A regular Allen wrench of three-inch length lets you easily get 20 to 25 in.-lbs., so there's no need to add leverage. If you have to lean your body weight onto a screw-driver to keep it in the slot while you use all your arm strength, you've over-tightened the screw. A lot.
To tighten a base in place, first hand-tighten it no more than snug from back to front. Then tighten it to full torque from front to back. Let the bases sit for a moment, and then give them an extra hand-torque from the rear screw forward to the front one.
The last step isjust to make sure they are all down tight, in case the base shifted slightiy as the next one in line was tightened down. With a torque wrench, follow the same pattern, but use the torque wrench in the middle set of tightening, and handhold the Allen wrench for the first and last.
For the same reason you use a star pattern when tightening the lug nuts on your car wheel. You want the wheel or base to settle down into position evenly and not be cranked down tight at one spot, which creates stress in the part as you then tighten down the rest.
ABOVE : Before attaching the bases, be sure that they sit properly on the receiver and use a straight edge to ensure they're properly aligned.
From here the process diverges depending on the exact ring system you use. For Talley rings, place the scope inside of one of the ring sets and hand-tighten the top screw enough to keep it all assembled. Place the ring and scope on one of the bases and install the lower screw and hand-tighten. Now that the parts will stay in place, assemble the other ring and hand-tighten.
Now you set the eye relief, align the reticle and keep them in place while you make the ring screws hand-tight until the scope is snug but not fully clamped. Then get the torque wrench (if you have one) or use the Allen wrench and tighten to full value, following an "X" pattern in sequence. Talley ring screws need to be tightened to 18 in.-lbs.
Weaver top-mount rings follow a different pattern. First, place the ring lower halves on the receiver bases and spin the big nut finger-tight to keep the ring halves in place. Check fit by placing the scope in the lower halves; make sure everything clears, like bolt handles. Once you're sure everything will clear, the base screw (the big-head one) gets 30 in.-lbs. of torque.
Now snap the upper ring bands over the scope. The trick here isto press the bent portion (the one with the screw holes) and not the shorter hook end over the scope tube. The bent end is smooth and won't scratch your scope tube. The other end has a square edge and might scratch.
Slide the short end into the slot on the lower half, insert the ring screws and hand-tighten them. Once the scope is in position, tighten the ring screws, keeping in mind that as you tighten you will be slightiy rotating the scope in the rings. So you have to have the scope reticle tilted slightly out of vertical—away from the ring screws before the last set of screw tightening.
Properly done, it ends up vertical. This takes practice, so don't be alarmed if you have to do the first scope two to three times to get it right. Weaver ring screws get 15 to 20 in.-lbs. of torque. Ring systems that use a straight-down ring don't have the "rotate as you tighten" problem.
Leupold uses a different ring/base method, one that has been in use for nearly a century now. In addition to the required wrenches or screwdriver, you need a way to adjust the front ring lower half and a way to check alignment. Do not use a wrench, even a padded one, for adjustments. Brownells carries the correct tool for both adjustments and alignment.
Once the base or bases are secure take the front ring and make sure the screws are firmly hand-tight. Place the dovetail base in the receiver base hole, and with a wooden wrench (a hammer handle that fits is perfect) give the ring a quarter-turn. Place the rear ring on the base and hand-tighten the cross bolts, but leave them loose enough that the rear ring can "float" but not fall out. Eyeball it to be more or less centered.
Remove the front ring top and lay the scope in the open U of the rings. Press the scope down into the front ring with your thumb and force it to find the center. Look through the scope and see if it agrees with where the bore is pointing. (This is where a collimator - or a window and a distant object - come into use.) If they do not agree, lift the scope out, tighten the front top ring back into place and use the wooden rod to turn it in the needed direction.
Once you have the front ring centered with the bore, you're ready for the tightening. Place the scope where eye relief will be correct. Place the ring tops on the scope and install the screws, but do not tighten them yet.
Check once again that the scope is in the correct spot and that the reticle is vertical. Now tighten the front ring hand-tight only.
Check alignment again and now direct your attention to the rear ring. Hand-tighten the base or windage screws—the ones that capture the rear ring—until the rear ring is caught in place and centered. You want to do this by hand because with a screw-driver it is too easy to over-tighten one side first, push the rear ring off-center, and break your scope. (You know how one of my customers found this out, don't you?)
Once the rear ring is centered - pinched between the screws and flat against the base - hand - tighten the top ring. Check alignment once more. See the recommendations for final tightening torque for the base screws. The windage screws get 45 in.-lbs. of torque.
A word about "insurance." I'm not too keen on using Loctite on scope rings. On the ring screws in particular, I found it to be a headache. Invariably, when it came time to change scopes or replace a damaged one, ring cap screws that had been "Loctited" made for extra work. Often I'd have to drill the screw heads off, and once the scope was out, use a propane torch to burn out the Loctite and remove the screw stubs to reuse the ring bottoms. So no Loctite on the rings.
On bases, I can see a drop, and only a drop, of blue, since it can be wrestled apart without heat. The tech guys at Weaver recommend blue Loctite and not much of it. You don't need more than a drop, and if you hose the base, you risk drips that will lock anything they squirm into. Leupold currently uses Nylok screws, but the older bases can also be given a drop of blue. If you are really worried that your mount screws will come loose, don't.
The process I've laid out, with clean threads and proper torque, won't come loose. If you are still worried, a drop of clear nail polish on the edge of the screw will both lock it in place and provide visible evidence if it should, somehow, come loose.
Screws are springs. You are flexing the threads as you tighten the screw.
If you try to make the screws as tight possible, you risk stripping the screw threads or the receiver threads or even breaking the screw head. I regularly saw scopes with cap screws or base screws that had half a head, the screw having broken at the screwdriver slot. They had been torqued too much.
An overly tightened screw is also going to be weaker under recoil, if the screw is already tightened to its maximum tensile load, tiring can be enough to put it over the limit, That is a particular concern with the big magnums, since their owners are more likely to overtighten. As a result, they can create the very thing they tried to avoid; a loose scope. They just did it by breaking the screws instead of not making it tight enough.
Screws have torque limits for a reason, and manufacturers mention them so you'll be happy. Torque wrenches need not be expensive. Fit-it sticks make a pocket wrench you can take into the field and Weaver makes one that won't quite fit into your pocket but also won't bust your wallet!
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QUESTION : I am taking delivery of a CZ 550 Deluxe rifle in .300 Winchester Magnum and a Trijicon ACCuPoint 2.5- 10x56 scope with Triangle Post Red reticle. The only item I haven't decided on yet is what kind of scope mount to use. What brand would you recommend?
ANSWER : A The integral scope bases on the CZ rifles is an excellent feature. CZ rings are strong and well made, but I have a preference for Talley rings which are available to fit CZ rifles. The rear ring has a projection to fit the notch in the receiver bridge to anchor the mount against recoil.
The Talley rings are precisely machined, and beautifully finished in smooth, non-reflective matte. The assembly is strong and rigid, allowing no movement from recoil. I prefer the fixed version, but quick-detachable rings are available as well.
New from the Lynx range are the 1" or 30mm scope rings for Brno, CZ550, 600 series rifles with 19mm dovetails in matte black with locking claw.
There is also the optional Picatinny rail scope rings available for Brno CZ Model 1, etc, with 14mm dovetail, made in steel.