Everybody seems to be fascinated with lasers, so why don't those who are really interested in bore sighting their muzzleloading cannon, just go down to your nearest Sportsman's Warehouse or Gander Mountain store and buy a cheap, bore sighting red laser? They cost 39 to 89 dollars and come with several standard plastic bore-centering bushings that fit over a 1/8 inch spud. For your cannon you will have to make or have made a centering bushing with an O.D. about .0003" to .0005" less than your bore dia. and also precisely drill and bore a close-fitting center hole to hold the laser's spud without any shake. We made ours from a scrap piece of 1.25" dia. brass rod 2.00" long. Next you will have to calculate where your cannonball will first cross the line of sight. Zeroed for 100 yards, our 9 oz. Brooke bolt crosses the line of sight at 35 yards where we place a slightly reflective laser target supplied with the laser. A plain, light colored, piece of paper will work just fine.
The big question is: At what distance from the cannon's muzzle will you place your laser target? For the answer to that, we go to an excellent, free, ballistics calculator website called JBM Small Arms Ballistics,
http://www.eskimo.com/~jbm/calculations/traj_basic/traj_basic.html When you get there look for
JBM-Calculations-Trajectory (Basic), because, unless you are a serious student of ballistics, that's all you will ever need. This is the best ballistics calculator we have ever found and we have looked and looked. It's easy to use if you look up few basic terms in their "Terms" list. Meanings are simply presented. The chart that we used to determine our 35 yard laser target distance is below and you can see why we picked 35 yards.
Calculated Table
Range DropDrop Windage Velocity Mach Energy Time Lead Lead
(yds) (in)(moa) (in)(moa) (ft/s) (none) (ft•lbs) (s) (in) (moa)
0 -5.0 *** 0.0 *** 1200.0 1.064 12589.4 0.000 0.0 ***
10 -3.2 -30.8 0.0 0.0 1172.7 1.039 12023.0 0.025 0.0 0.0
20 -1.7 -8.2 0.0 0.0 1147.3 1.017 11508.1 0.051 0.0 0.0
30 -0.5 -1.5 0.0 0.0 1123.8 0.996 11041.4 0.078 0.0 0.0
40 0.5 1.2 0.0 0.0 1102.1 0.977 10618.8 0.105 0.0 0.0
50 1.2 2.3 0.0 0.0 1082.0 0.959 10235.4 0.132 0.0 0.0
60 1.6 2.5 0.0 0.0 1063.4 0.943 9886.6 0.160 0.0 0.0
70 1.7 2.3 0.0 0.0 1046.1 0.927 9567.8 0.188 0.0 0.0
80 1.5 1.7 0.0 0.0 1030.0 0.913 9275.1 0.217 0.0 0.0
90 0.9 1.0 0.0 0.0 1014.9 0.900 9004.8 0.247 0.0 0.0
100 -0.0 -0.0 0.0 0.0 1000.6 0.887 8753.8 0.276 0.0 0.0
110 -1.2 -1.1 0.0 0.0 987.2 0.875 8519.8 0.307 0.0 0.0
120 -2.8 -2.3 0.0 0.0 974.4 0.864 8300.4 0.337 0.0 0.0
130 -4.8 -3.5 0.0 0.0 962.2 0.853 8093.9 0.368 0.0 0.0
140 -7.2 -4.9 0.0 0.0 950.5 0.842 7898.8 0.400 0.0 0.0
150 -9.9 -6.3 0.0 0.0 939.3 0.833 7713.7 0.431 0.0 0.0
160 -13.0 -7.8 0.0 0.0 928.5 0.823 7537.7 0.463 0.0 0.0
170 -16.5 -9.3 0.0 0.0 918.1 0.814 7369.8 0.496 0.0 0.0
180 -20.5 -10.9 0.0 0.0 908.1 0.805 7209.2 0.529 0.0 0.0
190 -24.8 -12.5 0.0 0.0 898.3 0.796 7055.3 0.562 0.0 0.0
200 -29.6 -14.1 0.0 0.0 888.9 0.788 6907.5 0.596 0.0 0.0
08 Aug 2008 21:36:31, JBM [http://www.eskimo.com/~jbm]
You can see from this chart that the 9 oz. Brooke bolt at 1,200 FPS crosses the line of sight 0.5" low at 30 yds. and 0.5" high at 40 yds., so we say, at approx. 35 yds the bolt will be really close to coincident with the line of sight.
Use the information to have some fun as you go out and actually do some projectile shooting! Please remember, bore sighting is NOT a precise method of aiming for bullseyes, but rather a method to get your projectile on the target paper at the selected range, and save you much frustration. In our case, this is almost always 100 yards. For a smooth bore of .50" to 1.25" bore dia. you might want to try 25, 50 or 75 yards to start.
Have fun!
Mike and Tracy