My Cool Rimfire Review of the Bushnell Magnetic Boresighter

         

Here you will find some useful information on my experiances with the Bushnell Magnetic Optical Boresighter Tool


Where to get:
Amazon.com  (search: for Bushnell Magnetic Boresighter)

Bass Pro (search: Bushnell Magnetic Boresighter) (they sell the Pursuit version)

Dicks Sporting goods (search: Magnetic Bore Sighter) 

Natchez (Search: Bushnell Magnetic Bore Sigher)


WARNING: Follow all safety guidelines in your firearm owner's manual, Scope manual as well as the Bushnell/Pursuit Optical Boresighter manual.  Double check that your firearm is clear of all ammunition, keep the muzzle pointed in a safe direction. Double check that the bore is clear of all materials before as well as after boresighting.

I am not a gunsmith, take all this information for what it is worth. I am a gun owner relaying my personal experience to others. Use common sense and your own better judgement with this information. This information is provided to help you get the most out of your magnetic bore sighter from my personal experiance and trials.

Definitions:
MOA
: Minute of Angle, 1/60th of a degree of rotation 1/21600th of a rotation WIKI page on MOAVideo on MOA
Windage
: The Left/Right adjustment typically on the right side of the scope
Elevation: The Up/Down adjustment typically on the top of the scope
Reticle : Often called Crosshairs by the common public. WIKI page onRETICLE

There is nothing wrong with following the directions in the manual and you can get within 10 inches at 50 yards. The accuracty of the alignment for such a device as this leads to the tendancy for very small amounts of tolerances to affect the represention of the True vs. indicated zero point. What I am saying is that in my experiance, the zero point in the optical boresighter (as well as my Laser Boresighter) is not perfectly zero. It is not expected to be either. These devides are for you to "get on paper" to do the final adjustment at the range.  What I am laying out here are suggestions for getting more consistancy and understanding the device better.

1) Measure the approximate distance from the center of the barrel to the center of the scope at the Objective End of the scope. Mark a point on the side of the Bore Sighter to indicate where you should locate the center of the muzzel to the Bore Sighter.


2) Attach the Bore Sighter to the front of the barrel. Center the Bore Sighter on the muzzle and align it as straight as you can.


3) Verify the Bore Sighter is straight, by viewing from the bottom side visually looking at the scope on the other side of the Stock (if you can see it) and then at the bottom of the Bore Sighter. I find that looking at it from the bottom side can help you visually get it straight.

4) Look through the Ocular end of the scope and view the Pattern.  Adjust the Focus on the scope if necessary. Move the Windage and Elevation to center the Reticle in the pattern (for illustation purposes the below image has a drawn RED reticle on the Bushnell Pattern.


5) Remove the Bore Sighter.  Go to the Range.  If possible, Shoot at a close a distance that is allowable.  Adjust the windage and elevation then move out to your normal shooting distance or perform your desired sight in procedure. Understand the ballistics trajectory of the bullet arc when adjujsting at the closer distance. Here is a shooter's calculator that is very useful. In my case, I know that if I want to zero my rifle at 50 yards, it also crosses the zero point at 25yds and 50ys with my .22LR using Mini Mags.  How convenient. I can zero at my local 25yd indoor range and when I next shoot at 50 yards  I'll likely be within an inch of center.

6) Next step after zeroing the scope, is to go back and then attach the boresighter.  You will find that the Reticle is No longer at the center. It may be 1 1/2 squares away. Draw a picture of where the reticle ended up for future reference.


Additional Talking Points and information:

1)  Asking the Bore Sighter to be prefect is asking a bit much in my opinion.  For example, If the mounting angle (left/right) of the boresighter is off by a few thousanths of an inch from one edge to the other, the reticle will move up to 1 grid line.  To illustrate this, sight your rifle and get the reticle centered. Now place a piece of scotch tape along the right edge of the magnet. Then  sight it again.  In my case, the reticle moved about 1 grid line to the right. Imagine how accurate the magnet needs to be glue'd in and the lenses? Any variation in the front surface of the rifle or misalgnment in the bore can throw the bore sighter off.  I so far have tested the bore sighter in 3 .22LR rifles. In each case, once zero'd, the reticle ended up to the left of center.  In the worse case (A Ruger 10/22 vs. a Marlin 795) the final reticle placement varied by about 1/4 of a grid line from one to the other.  (My Marlin 795 -Left and Marlin XT-22 Right alignment shown after zeroing at 50 yards). I did find that if I estimated the true center of the boresighter, using a known zero'd rifle, that I could get a better centering for a different rifle.  As shown below, using one rifle's true center would have gotten me closer to zero than using the center of the pattern. Each Bushnell Magnetic Bore Sighter I expect to be different.

2) This is a great tool for using when switching scopes or removing a scope temporary to use a fixed sight.  One of the other reasons I purchased this product was that I wanted to be able to work on my 25yd offhand shooting at a locan indoor range with my Tech Sights.  I'd have to remove the scope and attach the tech sights, then shoot. Then when I wanted to shoot at the outdoor 100yrd range, I'd have to zero the scope again.  Using the repeatable method above, I can mount the scope back up, check my true zero and be within an inch at 50 yards easily and quickly. Because of this process of re-zeroing the scope using the adjusted centering, I can save time because I can now pretty much start shooting after a quick zeroing of less than a 10 round magazine.  In the first instance of using this device, I noted the true zero point, then pulled one scope off of my .22LR rifle and installed the other scope.  I had to shim the first scope and also had to shim the 2nd scope (I need better scope mounts). But once I shimmed it and aligned the reticle to the same location as before changing scopes, I was able to then go to the indoor range and I was hitting bullseyes without needing to make any windage/elevation adjustment!

3)  I can easily tell how much windage and elevation adjustment is remaining.  On one of my scopes, when you get to the end of the adjustment, the turrets don't offer any resistance. They just keep spinning. I could tell this visually because the reticle stopped moving.  Without seeing the reticle moving, I could not tell where the endpoints of my adjustments were. knowing the end points help you to estimate the center point of the adjustments which is where you want to have your scope when you mount it and mechanically adjust your mounting.  

4) With a lose scope ring, you can rotate the scope and optically verify your windage/elevation are centered.  If you rotate the scope as far as you can clockwise, then slowly rotate counter clockwise, you should NOT see the center point of the reticle move from the position on the grid. If it wobbles around, you have to adjust your windage/elevation to center it.  A scope works best if it's closest to center when zero.  This keeps you from running out of adjustment range when you are in the field or need to add more elevation to get that longer shot.  If you find yourself running out of elevation, go and zero the scope for a close distance, then note the zero point on the grid.  Go back and get the windage/elevation dials optically centered. Then shim the scope (Burris Z rings, beer can sheets, base mount shims, what ever). Get it mechanically shimmed the best you can then try again. You may even want to mechanically center your scope at a medium distance so your able to use more of your adjustment range.

5) I was able to use this device and compare my zero position for both 9X and 3X knowing it was still aligned up to the same point at 9X as well as 3X, gave me confidence that I could lower my zoom at the 25 yd indoor range and know I could keep a zero.  Below are images at 9x and 3x for the same rifle.


6) More pictures of the Bore Sighter.  1X view using camera directly onto the bore sighter.  View of the mounting magnet. View of the back end of the bore sighter.  How I illuminated the bore sighter so I could take photos (I used a 35mm digital SLR. Focusing and aligning the camera or video camera is a pain!)


7) Because this device is optics and you dont' want anything lose, handle this with care and DON"T DROP IT!

8) Although most of the reviews were positive and they used the same device at the store where I purchased my rifle, I read some negative reviews on this before buying. But I think the negative reviews were because those people were either using it inconsistantly (I hope my above notes are helpful for that) or they had unrealistic expectations (I read someone complain they were not on paper at 100 yards).

9) Once you sight in your rifle, you can then check to see how much room for elevation adjustment you have remaining.  For my favorate 22LR ammo, I know that the move from 50 to 100 yards is approx 6 MOA (24 clicks from a 1/4 MOA per click scope). After I zero the scope at 50 yards, to verify I have enough elevation adjustment left to shoot at 100, I attach the Bushnell Magnetic Boresighter, then go 24 clicks of up. The reticle should continuosly move down in the grid for 24 clicks. I'll ahead and go 30 or 40 clicks and see how much room I have. My point is to know how much room you are going to need and use the device to verify it before you run out and try shooting a longer distance.  (remember the shooter calculator, that's just an estimate, try to use real world trials to see the MOA difference in your rifle, your ammo, your scope).

Useful Links:
Chuck Hawks review of the Bushnell Magnetic Boresighter
Leupold Zero Point optical Bore Sighter (higher end product) Video

Twin City Rod & Gun guide to Bore Sighting (2004)
Optical Centering Fixture Video (you can do this with the Bushnell mounted to your rifle, just cant the scope clockwise and counter clockwise.