A Method for Obtaining a One or Two Shot Rifle Boresight Zero
Updated 3/31/10
Until today, it has been too cold for the old bones to go outside and boresight my new rifle/scope setup. As such, I have had plenty of time to research the topic and come up with an alternative, better, set of directions to get the job done over what most laser bore sights come with.
First, mount and level the scope with the
Wheeler level-level-level kit or with two small spirit levels that might be had from your local home improvement store. This will get your rifle and your scope on the same vertical and horizontal axis. You might have to get creative with finding a spot on the rifle to place a level. The top turret of the scope generally works for the second level.
Next, get a laser boresight. I chose the type that fits into the chamber and projects the laser beam right down the barrel. These can be had for as little as $25. I chose the chamber boresight made by
Sightmark as it is solidly built, fully chambers in my Savage 10 fcp and is on the money as far as the laser position indicates. The device does not use sleeves, a plus in my opinion. It would seem to be a bargain at under $30 not including shipping. I would advise that you lay in two sets of spare batteries. My Sightmark uses two small button batteries that lasted about 20-30 minutes in daylight, even though the target is in light shade. Battery life in other makes may be under one hour.
Place some plastic wrap over the end of the barrel. Make sure the wrap covers the bore smoothly. No matter the type of in-chamber boresight you choose you should do steps A thru C at least once to check centering.
A. Then, turn on the laser and insert it into the chamber. Gently snug but do not fully close/seat the bolt. Without looking directly into the bore or at the laser beam, note where on the wrap the laser is hitting. It is likely not perfectly centered in the bore.
B. Open the bolt, remove the laser from the chamber enough to give it a 1/4 turn clockwise. Reinsert laser, snug bolt, and observe where the dot hits. If not centered repeat step B until the laser is centered in the bore.
C. Carefully remove the laser straight back out of the bore and note the location on the laser that is on top. Make a mark so that you can repeat the location when we go outdoors to finish the sight in process.
I decided to use premium ammo to do the range zero. I selected Federal 168 gr, .308, Gold Medal Match. I looked up the ballistics data on the Federal website. I then used the
FREE Point Blank ballistic software from the guys at
www.HuntingNut.com to get the data for a 100 yard zero for my ammo. Point Blank tells me that with my scope mounted 2.1 inches from the bore, center-to-center that
my laser beam will hit a target at 25 yards, 1.1 inches below the point of aim. Using a free, fine-lined target found on the web I marked a spot on the target exactly 1.1 inches below the center-cross-haired bulls eye.
On the next Finally, a decent day, I ventured outside and set up the rifle in a gun vise positioned to aim at my custom marked and leveled target. (I used a carpenters level to set the target, this so I can check my scope reticle level.) I measured the 75 feet as being from the target to the mid-point of the scope, lengthwise and the front end of the barrel. This advice was found on the "Horus"
http://www.horusvision.com/ website and makes good sense. Long distance shooters may wish to take a look at their products. I leveled the rifle using spirit levels, as described above.
I then repeated step B above and confirmed that the laser spot is in the middle of the bore. I then centered the laser on the marked spot, 1.1 inches below the center bull. Note that the laser beam is about one-inch in diameter at this distance and not uniform. That done, I adjusted the elevation and windage until the scope cross hairs are centered on the bull. With my 20 MOA base, I will have to come down 24 MOA, I think, as each click will be 1/32 inch at 25 yds. The above assuming my reticle is centered in the elevation and windage range of the scope. Note: The reticle leveling done in the scope mounting process was on the money.
Finally, after a couple of weeks I had a chance to go to the range on a windy 65 degree day. The first task was to break in the barrel on my new Savage 10 fcp using the David Tubb, Final Finish process. Before the break-in I fired one shot at a 100 yd sight-in target. The shot was 5.5 inches low and 2.5 inches left. (I had hoped for better.) Wind was cross range from the left rear at a flag snapping 20-25 mph. I then followed the Tubb process, firing 20 rounds of his specially coated ammunition in groups of 5 with a thorough bore cleaning at the start and every five shots until finished. I used a moderately strong copper removing cleaner,
Sweet's 7.62. I expected to see a fair amount of copper fouling which many had said would be the norm. Surprisingly, I observed hardly any copper fouling from start to finish. The faint blue on my patches can probably be attributed to the phosphor-bronze brush used in the cleaning. Other than having a very finely made barrel, I can't explain the discrepancy in what I was led to believe from multiple sources on other websites. On finishing the Tubb break-in, I fired one more Federal Gold Medal Match and noted that it targeted about 1/2 inch higher than my first Federal GMM, fired from a pristine virgin rifle.
After adjusting the Millet 6X25 30 mm Buck-Gold scope for zero, I fired four 3-shot groups. Each group was from a different manufacturer these being Federal, Ultramax (re-manufactured), HSM, and Corbon. Except for the Ultramax, the quality of the ammunition was graded as match. Another surprise! Firing from a bipod on a bench in a stiff crosswind I managed to get
two .9 in, c-c groups, a 1.1 inch and a 1.15 inch group. It would appear that my Savage 10 is a winner. Once again, the cleaning was quick, easy and showed almost no copper fouling.
To restate, my original theory was that I should be able to go to the range and be close to the bull with my first shot at 100 yds. Given the low budget laser bore sight, which I suspect was the cause of my less than hoped for first-shot accuracy I will contend that the methods used did achieve the goal, obtaining good results at low cost. It is almost agony to see a guy fire a whole bunch of rounds at a target only 25 or 50 yards away and consistently miss by a bunch. If this method helps avoid all the possible mistakes that Murphy says can and will happen, then maybe the extra care and steps involved is worth the effort.
Should I get the chance, I would like to try the method again with a higher quality laser such as the products made by Site-Lite.
Next time out, I will set up a vertical marked target about 30 inches high with a bold vertical line, in the middle, from top to bottom, and a bold horizontal line from side to side near the bottom. I will use this target to insure that my scope is not canted to the left or right, using a live-fire technique. Cant can be a major problem at long ranges.
Now, I realize that most any method that will get you on the paper at 100 yds will allow you to refine your zero point with
X number of cartridges fired. My procedure was a challenge to see if a theory, developed on a cold Winter day, could be successfully put to practice thereby saving $1.80 per shot several times over.
Beer Nuts
AKA Roger
Guns have only two enemies; rust and politicians.
