It should be simple. You buy the mounts, screw them on, and bolt on the scope. If everything is made right, you should be close enough to just tweak the crosshairs, and it's zeroed!
But, any experienced engineer will tell you what Murphy's law of mechanical assembly is: Tolerances accumulate unidirectionally towards maximum difficulty of assembly (or in this case, maximum divergence from bore center.)
There's lots of reasons for this. Barrels do not screw into actions at the exact same angle every time. Tooling and jigs for scope-hole drilling&tapping ages and wanders. Stamping machines for aluminum rings age and warp. Manufacturers change their method for making receivers, and the mounting surfaces are shaped a little differently. And of course, not all mounts and rings are created equal.
There are consequences, as well. Warped and bent scope tubes that will lock-up and not adjust, scopes cranked out to their maximum adjustment (and far outside their ideal optical center), or total inability to zero.
Even if you don't have a bore sight, you can follow this advice to properly align and lap the rings. You may have to dissasemble the mount later to shim it, but if properly done, the rings will fall into place more easily. Get used to the idea that you will assemble and disassemble several times, no one can get it aligned perfecty the first time.
Starting with the type of mounts, the worst is two piece Weaver-style bases with aluminum rings. There is no provision for adjustment, vertical or horizontal. How they screw on, is what you get. If all the holes line up and your receiver is parallel with the bore, then they will work fine. If not... If you bend them after installation with a long 1" wooden dowel, well, aluminum just doesn't take to bending without stress cracking. And you really can't hold the two mounts lined up together and somehow still tighten the one mount with the ring installed. Until they put a big hole in the ring to stick an Allen key through, it's hit and miss.
Another problem with two piece mounts is shimming. Let's say the front mount/ring is low and needs to be shimmed. Go ahead, but now it is mounted on a different plane then the rear. Shim it with a wedge shaped shim, that's better, the front ring angles back to point towards the rear, but the rear ring is still pointing level and will crimp the scope. Sure, you can lapp it, but you'll be removing large amounts of ring! What you need is a much thinner, wedge shaped shim for the rear mount, too. Now both your mounts are sitting on shims, and you have to work extra hard shaping the shims to get them all pointing in the same direction.
With a one piece mount, you just shim under the front or back, and you're done.
A one piece Weaver base eliminates most of the external ring-to-ring alignment problem. It still leaves the overall alignment question, and variances in the rings themselves. Even if you have these mounts, go through the whole lapping procedure described- you'll still need it. You might even be fortunate to have them line up fairly well with the bore, but that doesn't mean that they line up with each other. Going with a quality helps. Just because they are all called Weaver style, doesn't mean that the Weaver brand is any good. There's a reason Weaver-style mounts and rings by other companies sell for much more.
Redfield (and Burris and Leupold) make one piece bases of solid machined steel. These Redfield-style bases have a windage adjustment built-in. Like Weaver bases, they should be shimmed underneath to compensate for large difference in height, when dealing with sloping receivers or misalinged barrels. I have found that a cartridge casing, sawn off 1/3 of the way up from the base, cut, flattened and deburred, makes an excellent, wedged-shaped shim. Flattening the thick end with a hammer can reduce the angle of the wedge. Test fit it, score the excess with a sharp point, and mark the hole with a punch. Drill it against a piece of wood and then trim it, and it's ready to go.
Moving on to the rings, there are cast aluminum, aluminum with stamped steel caps, and forged steel. When aluminum ring manufacturers compare themselves favourably to steel, it's the stamped sheet-metal steel caps they are talking about, not the forged type. Many of the steel cap type rings screw on diagonally, which produces maddening diagonal shifts in zero when boresighting.
Mountless see-through rings have their own flaws. They hold the scope too high for good accuracy. Scopes, like iron sights, should be held as closely to the bore center as possible. They screw on with self-centering conical screws, which allow for no adjustment. Being cheaply made, they are usually well out of round. And being tall, they subject the mounting screws to substantial leverage when bumped.
I used to wonder why no one made quality steel see-through rings... since they are a poor compromise at best, I think I now understand why.
Your mission is to get both rings at the same height, vertical and horizontal alignment, and that alignment pointing parallel to the bore. But first, you have to deal with the individual irregularity of the rings.
When you are done shimming the base and have the rings in place, set the scope in the rings and check for air gaps. You will have a very difficult time centering the scope until these gaps go away.
Cheap rings in particular, just aren't very round. Even if they are, and they line up perfectly, they may be a little undersized, or the scope tube oversized. This is why lapping is necessary. First align the rings on the mount as well as possible. Wrap your 1 inch dowel in 400 grit wet/dry sandpaper, and staple it tightly down, or coat it in coarse lapping compound. (Bench rest and precision shooters may blanch at my choice of tool. Please understand that these instructions are for hunting rifles and standard sub-$100 mounts, which rarely see this kind of necessary attention. If you know about the more expensive ring lapping tools, well, you don't need to read this page. This is, after all, the Cheap Scope Page!)
Watching the staples, lap each of the bottom rings until the high spots and edges are worn down. Stop, wipe, and try the scope often. As it gets close, switch to 600 grit or fine lapping compound. When the scope settles fully in place in each one, try the scope in them together. Turn or adjust the rings as necessary (if adjustable). Finally, lap them both simultaneously with the dowel. When the scope settles into place without force, you're done. If the caps are near 180 degrees around, they may need some lapping too. For final lapping, fine lapping compound on the bare wood dowel will finish the job.
When you are done, removing the caps and remounting the scope results in practically no shift in zero. If this is not the case, try to figure out what's out of alignment, and adjust, shim, bend or lap it into submission. Don't apply a lot of torque with a long dowel to aluminum rings, mounts and/or receivers- they just can't take it. You'll rip or strip the screw holes. Steel setups can take some bending, but don't get carried away.
Never place a shim inside the ring. This is the mark of an amateur (*ahem*, I've been there). There are several reasons. It reduces the scope-to-ring contact surface, allowing slippage. Tightening to compensate will crimp the scope in the other ring, because it enters that ring at an imperfect angle. Finally, it is ugly. Always shim the mount, between the mount and the receiver. Use the shim material nature provides you- brass cartridge case for steel receivers, and aluminum soda cans for aluminum receivers.
When you are finished, you will have a solid, firm mount. It won't shift or work loose. It will allow removal of the scope and replacement with little or no rezeroing, because the scope is not stressed, bent or twisted. Finally, it puts the scope very close to the correct zero. So, take it all apart and put blue Lock-Tite on the mount screws (but not the ring screws), put it together, and read How to Zero Cheap scopes.
And remember to get those crosshairs straight up and down.
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If you're putting, say, Weaver brand aluminum mounts on a Ruger 10/22 and need a shim, well, everything's aluminum. A soda can will do the trick. (That's a Pop can for you Westerners.) (Be careful. Until recently, Crown Bottling on the East Coast was using steel cans so thin, people thought they were aluminum). If you need it wedge shaped, fold it over along one edge and beat it flat. Make sure the edge is folded and beaten thoroughly, you don't want any slack.
Thicker shims are properly made out of brass flat stock. If you don't have any available, cartridge brass can be used. Remington tends to be thick and soft, PMC springy, etc., so keep that in mind when choosing stock. If you cut it off near the base with a Dremel cut-off wheel or hacksaw, you'll see that it's already tapered, making it easy to beat into a flat, wedge-shaped shim. If you want a very shallow taper, cut a long cartridge case as far away from the base as possible. Whatever you make it out of, you'll need to beat it with a hammer and file the edges.
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When working Hunter Sight-In, I had about 25 scopes come through for bore alignment and adjustment. Of these, most were inexpensive Tasco's and Bushnell Sportview 3-9x32mm scopes, the kind you can buy at your local X-Mart for less than $50.00. For those of you trying to sight these scopes in, or considering buying one, here's the procedure I worked out for adjusting them. The instructions assume 1/4 minute-of-angle adjustable sights. If you have 1/2 minute adjustable shotgun or rimfire type sights, simply use half as many click adjustments. Some smooth-adjusting scopes have 2 minute markings, but can be infinitely adjusted.
These intructions assume you have the mount and rings correctly installed, like this.
1. Install the mount. The receiver of old guns, shotguns or military guns may have to be drilled and tapped. Problems of left to right alignment can be compensated for, by using an adjustable mount, like the Redfield. Vertical alignment problems, like the gun shooting extremely high, should be fixed by shimming up the mount under the base, not shimming the scope in the rings. Some guns, like Savage 110/111/112 and the Springfield 1903A3, have sloping receivers that are not parallel with the gun bore. Scope mount manufacturers should be hounded until they make a decent scope base for these guns.
When the mount is properly installed, the scope whould be set in the rings and point roughly at the target, within 1/2 foot at 100 yards. Install the ring tops or place (moderate)downward pressure on the scope while verifying this. If you find that moving the mount/base/rear ring in either direction causes scope deflection in only one direction, a ring is not in perfect perpendicular alignment, and the scope is riding up on one side of the ring when adjusted to that side.
Never use the scope to adjust the alignment of the rings. Leupold makes a ring wrench, but a one inch dowel, thin broomstick, etc. makes a perfectly adequate tool.
Mounting scopes (not adjusting them, though) is like using iron sights. Move the rear of the scope in the direction you would like to change the bullet impact. Move the front of the scope in the opposite direction. For example, if the bullet is hitting to the right, you may move the rear of the scope to the left, the front of the scope to the right, or a little of both.
2. Bore sight the scope by either using a colluminator, or by removing the bolt and visually sighting though the bore at the same distant spot as the scope. Shotgun barrels may be removed to do this, if possible, and an empty shotgun hull with the primer removed (hit it with an icepick from inside) may be used to reduce the field of view. While this method may seem crude, it produces as good a result. The primary difference is that changes in scope alignment can't be quantifiably measured.
Bore sighting by eye is best done at the range by pointing barrel and scope at the same 100 yard object. Use the scope mounting system for rough alignment, save the finely graduated scope adjustment for later. If the rifle is a semi-auto or other fixed barrel gun, a pen flashlight may be used to shine a light on the wall about 6 feet away. Align the scope at a spot directly above the light, about an inch closer then the height of the center of the scope above the center of the bore.
3. Check to see that the action is firmly mounted on the stock, that the muzzle is undamaged, that the bore is clean and empty of obstructions, that the scope mounts are firm, and the rings are tight (but not crushing the scope).
4. Show up at the range with screwdrivers, a steady rest for the bench, and lots of the same kind of ammo for sighting in. If you have a few oddball loads or cheap mil-spec ammo, you can use it for the throw-away shots and the 25 yard sighting, and save your good ammo for the 50 and 100 yard sighting. You'll see what I mean as we move on.
5. Fire 3 throw-away shots into the bank. If it's a .22, fire a whole box. This will (hopefully) get the crosshairs to settle into position. Check mount tightness. Fire a 3-4 shot group into a large sheet of paper at 25 yards. If the group strings (falls into a line), fire another group. If you fail to get a tight group anywhere, after several tries, return the scope. It's wandering. If you are not on the paper at all, remount the scope.
6. For 1/4 minute click adjustable scopes, it takes 4 clicks to move the scope 1 inch at 100 yards, which means that it takes 16 clicks to move it 1 inch at 25 yards. You don't want to move the scope more than about 75 clicks from center. Even if it goes farther, you will have problems with parallax and future adjustment range. So, if you are more than 4 inches to the left or right of the point of aim, remount the scope. If it is low, do not adjust it. If it is more than 3 inches high (unless its a shotgun) remount the scope. If there is no height adjustment, brass flat stock or even an aluminum soda-can's body serves as good shim material, if necessary.
7. Once the scope is mounted within 4 inches horizontally and 1 inch high to 5 inches low vertically (do not measure diagonally) at 25 yards and you can fire a consistent 3 or more shot group, you can continue with the fine adjustment.
8. The dials are labeled for bullet impact, not crosshair position. First, move the horizontal placement. If the bullets are hitting 2 inches to the left of the 25 yard bull, move the windage adjustment 4 clicks per inch X 4( for 25 Yards) X 2 Inches or 32 clicks. Tap on the center of the scope with a rubber or rawhide mallet. Move the windage an additional 32 clicks. Tap it again. Then move it back. Tap it again. Fire a shot into the bank. Now, fire a three shot group. If the group strings (forms a line) toward the center of the bull (above or below, it doesn't matter, we will do elevation later), continue firing until they all hit roughly the same spot.
9.By the way, on a cheap scope, don't expect those 1/4" clicks to actually move the reticle (cross-hairs) 1/4 inch at 100 yards. Also, large adjustments in one axis is likely to cause deviation in the other, usually towards the center. For example, if the scope is 20 clicks left of center, and is adjusted 40 clicks upward, it is likely to deviate several clicks to the right.
10. If the gun is a slug firing shotgun or .22 rimfire, do the above procedure with elevation until the bull is zeroed. If it is a high power rifle, do not adjust elevation until firing a group at a 50 yard bulls-eye. Remember to over-adjust, tap, readjust, tap, and fire a throwaway shot to get the crosshairs to settle. At fifty yards, a 1/4 minute click-adjustable scope requires 8 clicks adjustment for each one inch of bullet placement.
11. When the gun is zeroed on the 50 yard target, you may want to zero it on a 100 yard target. Be sure and maintain the same sight picture with each shot. That means the view through the scope should be fully dialated and your eye centered. Turn down the magnification if necessary. Don't be surprised if the best that can be accomplished is 4 to 5 inch groups. Those one inch groups usually only happen on the first go-round for Gun Magazine writers using windless indoor shooting ranges, (and people who develop handloads by tedious experimentation), and then only with a $400 (or more) dollar scope. If it's taken a lot of shots to get to the 100 yard line, you may need to let the barrel cool for a while.
12. Once you are satisfied or exhausted, don't touch, bang, or knock the gun or scope through the end of hunting season. Don't target shoot, and rezero if you shoot at game and want to continue hunting. Then, start saving your money for a real scope.
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