Authority to the Airgunning World

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Wednesday, August 30, 2006

Installing Rifle Scopes and Mounts

Once you have determined the right scope and mount combination to mount on your gun, degrease all screws and contact points the scope and mount touch. Typically, the inside of the scope rings, mount rails, and screws. I use Beeman’s degreaser for this job. For the screws, there are other degreasers such as brakleen, carb/injector cleaner, naptha, etc. Use whatever you feel most comfortable with.

Read any directions that come with the scope mount. These instructions can answer most of your problems and concerns.

Use a white piece of paper as the backdrop, and set it upright where you want to vertically align the crosshairs of your scope. Minimum distance should be 10m. Find a nail/hook you can tie a string around. The string I prefer is fishing line hung from the ceiling with a hook purchased from Home Depot, and a fishing sinker attached to the end of the line.

If your using a standard 8.5 x 11” white paper, paint the fishing line black where the white paper and line intersect. A birchwood casey flat black touch-up pen works well. When vertically aligning the crosshairs, I found this setup easy to see.

Secure rifle in rest or gun vise. I prefer a Hughes ballistic bag filled with poly pellets so I can easily adjust for eye relief. You want your scope to rest about three inches from your eye. Take a piece of tape about two inches long. Shoulder the rifle, and place the tape across the comb of the stock under your eye. Now place your rifle on its side on your bench. Place the scope on the bench above the action, with the rear of the scope three inches from the tape. Note the location of the scope mount screw holes. If your bells or boss ride right over the screw holes, you may need an offset ring. You will not have a problem with full-sized scopes. The probem usually comes up when you put a compact scope on the rifle.

I have a gun vise, but I won’t use it because I’m not able to shoulder the rifle during the scope and mount installation process. You can purchase a ballistic bag at cabelas, , and purchase the poly pellets at your local Wal-Mart. Located in the crafts section, poly pellets cost approximately $2 per 2 lb. Bag, You’ll need between 6-7 bags if I recall correctly.

To make sure the rings aren’t out of alignment, I use Wheeler Engineering’s 1” scope ring alignment and lapping kit:

highlights of the instructions if you don’t have the kit:

  1. Misaligned rings cause stress on the scope tube, which can dent the tube, distort the reticle, and cause adjustment problems.
  2. Properly aligned rings create more surface contact with the scope tube to keep scopes in place during heavy recoil.
  3. Keep ring pairs together and do not reverse top halves on their bottom halves. Most rings are manufactured as a single piece before they are split.

Put the mount on the scope rail. Lightly tighten the mount to the receiver so it can move back and forth, but will not fall off the rails. For a great majority of my mount installations, the mount is approx 1” – 1.5” forward from the end of the receiver cap. Then finger tighten the mount screws by alternating every half turn. If you use rings with a scope stop pin like the Beeman 5030s mount, make sure that the pin isn't bottoming out in the hole on the receiver. This will prevent the mounting claw from gripping the entire groove and the ring will not mount squarely. The fix is easy, just push or drive the pin into the ring a little farther. Note: if you are using a BKL mount, you might need to widen the mount to fit in the receiver rails by removing the clamp screws and placing them into the spreader holes. This procedure will remove the bluing on the end of the screws spreading the mount. Once mount fits in the grooves, completely remove the screws and paint their ends black again. I use a Birchwood Casey flat black touch-up pen for this job. Otherwise, you’ll see alternating black and silver on the opposite end of the BKL mount. I used two coats from the Birchwood Casey flat black touch up pen to take care of this.

Put the scope in the ring saddles, and lightly tighten the screws by alternating every half turn. The scope should be just loose enough so you can move the scope back and forth with little effort.

Adjust scope for eye relief. I like to look away for a few seconds, and then shoulder the rifle. Make sure the entire picture can be seen. If you see black anywhere keep adjusting. Strive for consistency on the cheek weld. The hold must be comfortable for your style of shooting. I probably do this 10 – 20 times until I’m satisfied with the eye relief.

Once you decide on proper scope and mount relief, it’s now time to align the reticle.

The easiest tool I’ve used for aligning reticles is the Vertical Reticle Instrument by long shot products. Follow the instructions it comes with the tool, or follow the directions on the website. They are the same directions. This tool is no gimmick; it really works.

Once you have the reticle, mount, and eye relief the way you want it, tighten down the screws on the mount, then the scope rings. Use alternating half turns. Up to this point the screws are finger tight. If necessary, use only medium (blue) locktite on the scope mount screws. Using loctite on the saddle ring screws is not necessary.

The easiest tool I’ve used to apply the correct tork tension to the screws is an Anschutz AHG inch pound tork wrench available from either:

Cat. # is 4506-SW4

You can purchase other inch pound tork wrenches, but I’ve never used them. This guide only uses the Anschutz inch pound tork wrench in the example.

In addition to the tork wrench, you’ll need a sears 2 7/8” magnetic bit holder to use your favorite allen head/screwdriver tips (such as b-square removable tips). You can purchase the bit holder at Sears for around $5.

In my experience with sportsmatch and BKL mounts, 55-60 inch pounds is adequate for both ring saddle and mount screws on magnum springers. I’ve taken off scopes after this tork procedure, and no scarring or scope tube compression has been witnessed. From message board readings, inch pound tork values range anywhere from 50 – 65 inch pounds. BKL recommends 25 – 35 inch pounds when using their mounts on rimfires. For magnum cartridges, up to 54 inch pounds is needed.

If you are using an anschutz inch pound tork wrench, you’ll need to convert Newton meters to inch pounds. Use an online torque conversion calculator like this one: In my experience, tork values are between 55 - 60 inch pounds (6.22 – 6.78 Newton meters) on the wrench.

After installation, you’ll need to verify that the scope and mount do not move.

To make sure nothing moves after completing setup, use masking tape. For the mount, place a strip of masking tape in front of the mount. For the scope, place a strip of masking tape behind the front ring saddle. If anything moves, it will be towards the rear of the gun. You’ll clearly see a gap between the masking tape and ring/mount if something moves. If you ever have any doubts about scope/mount movement, this procedure will reveal if anything has moved at your next shooting session. You can also apply correction fluid (white-out) at the 12 o’clock position on the screws. Make sure to remove masking tape after your shooting session. Masking tape has been known to discolor finishes.

Various Notes:

Custom droop vendors - Mac1 and BKL direct. At the time of this writing this service is $25 above the cost of the mount:

But be prepared to replumb- scope set up *can be* a very sensitive equation if you like to shoot at random distances accross the entire range that your rifle is most competent to shoot consistently.

It will throw your zero off *minimally* if you can manage to retighten the dovetail screws on the scope mount pretty close to your previous set up. Less so if you're using a one-piece mount. Even better if you happen to own a torque wrench with an allen set and can keep the ft lb of torque near identical.

Whether it's your zero, close range, or terminal POI- something's going to change. Just be prepared to tweak.

That probably took a little time to get everything to sit just right. I've been wondering about the scope levels and people who use plumb lines or regular levels to set up their scopes. I've never used a scope on anything until I got my R9 and I just bolted the thing on and made sure the crosshairs were squared up vertical and horizontal when I look through the scope.

The gun is hitting where I put the crosshairs. Since I didn't use any levels or plum lines did I have some sort of happy accident setting my scope up?

By eye is usually close enough-- if you're good at it. The problem is that many shooters don't hold a gun truly perpendicular to the real horizontal plane. I've picked up various shooters guns and noted that the crosshairs can be off a couple degrees. If you only shoot at one distance, it's no big deal,but if you shoot at varying ranges, it will affect your POI.
A few other notes: commercial levels can be off and the top of breechblocks aren't necessarily dead square to vertical. We can assume they are close, but never assume they are perfect. I have a precision machinists level (expensive) that is correct to within 2/10,000ths" in a foot and one day I was checking several other contractor grade levels I had lying about. Every one of them was off... some considerably. I've also found some dovetails on guns were machined at less than perfect angles, so never assume they are dead-nuts either.

...align the vertical crosshair with the vertical axis of the bore, odds are that your pellet will have a windage error (deviation) of some meaurement in its trajectory (say from 15 yards to 45 yards for instance). That could be a left to right, or right to left as evidenced by POI accross distance...

With that error in place, if you zero at a chosen distance, say 25-30 yards, you've adjusted your Aimpoint at that distance with the windage and elevation adjutments on your scope to converge with the POI/trajectory at that distance. The windge deviation will become evident by taking a shot inside that distance (say 15 yards) and then past it (say 40-45 yards).

A vertical crosshair that is in alignment with the axis of the bore will help you minimize windage errors accross distance right out of the gate. A ScopLevel will help you bank on that set up by helping you keep the rifle level from shot to shot.

Getting the vertical crosshair plumb is one part of the equation. If after you do all the above windage deviations are still unaceptably aparent, you can use windage adjustable mounts such as the Beeman 5039s (or BSquare) to bring your vertical crosshair into alignment with the axis of your bore (ie. bore-sight the vertical crosshair).

BKL Technology mounts are notoriouly known for being machined for precision when it comes to minimizing mount-induced windage errors... but the machining on your scope dovetails and the alignment of the bore relevant to the dovetails needs to be good enough to not require windage adjustable mounts to begin with.

Having said all the above, bare in mind that a margin of error is acceptable if it's predictable at a particular range and you can compensate for it with a little 'aimpoint english' on your part.

Additional resources:


Anonymous Anonymous said...

Thanks. That was Godlike of you, but I'm Agnostic.

6:33 AM  
Blogger jaspreet singh said...

nice post for more information about scopes visit gun scopes

10:06 PM  

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