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 and Banner 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. If you have a quality scope, you can follow these instructions, just don't overadjust so much and you needn't fire the settling shots.
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 (so far I've had Savage, Ruger, Remington, sporterized military Mausers and the Springfield 1903A3) have sloping receivers that are not parallel with the gun bore. Scope mount and rifle manufacturers should be hounded until they make combinations that actually work together.
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. Roughing-in by peering through the bore (bolt removed) and the scope at a large 1 foot target at 100 yards works well. A good, steady rest helps the process.
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 (up), a ring is not in perfect perpendicular alignment, and the scope is riding up on one side of a ring when adjusted to the 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. also 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 limited, 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 yet. 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 then only with a more expensive scope and a vendor-selected rifle. 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.
If you are following the procedure above and nothing seems to work consider these possibilities.
Horizontal adjustments affect verticle. Sometimes the problem here is the scope has been adjusted near its maximum windage (L-to-R) setting. Then when elevation is adjusted, the erector tube rides up or down the side of the scope tube, following the curvature of the tube and affecting the windage.
Verticle or horizontal adjustments have no effect. Scope adjustment is bottomed-out. Usually it is the mounts that have to be corrected first.
Shots go everywhere, no matter how careful I am. The scope could be totally FUBAR, or the mounts loose, or the gun might have a serious accuracy problem, like loose bedding. Another possibility is poor ammo selection, such as too-long bullets in a slow twist rifle. If this case some will eventually hit sideway, making a tell-tale key-hole mark. Check all stock and mount screws, try different ammo, swapping scopes with a known good scope.
For more info, read this page on Accuracy.
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