Re: Oehler Model 12 chronograph
Oehler Model 12 Chronograph
If you have the tables it is pretty easy to use. You have 2 "Sky Screens" (mine are Sky Screen-2 aka SS2). You mount the SS2s on a bar of some kind at either a 5ft or a 10 ft foot spacing. The 10 ft. spacing is better for higher velocities.
The bar with the 2 SS2s mounted on it needs to be on a stand so that it is a bit below the bore of your rifle. (Many people have shot their chronograph, so be sure it is below the bore.) I usually locate my rear SS2s about 3 to 5 ft in front of the muzzle and 6-12" below the line of the bore. The bullet path must pass over both sky screens to get a reading.
The cable from the rear (closest to the muzzle) SS plugs into the model 12 "Start" jack and the cable from the front plugs into "Stop" jack. That is the setup, now onto making a velocity readings.
1) Check your rifle bore to make sure you are not going to shoot the Sky Screens.
2) Place the rotary switch at the black dot (first digit position 4)
3) Turn the power switch on the Model 12 to Off/Reset then to On.
4) Fire your rifle
5) Determine the "Count" by using the 12 position rotary switch and the indicator meter (my meter has the words yes and no in the display).
Note: The unit uses octal counts (base 8 vs. base 10). I am an electrical engineer so octal is no big deal for me. In base 8 you can have any value from 0 to 7 (0 to 9 in base 10). A value of 7 is going to occur by adding 4+2+1=7 and a 6 would be 4+2+0=6 and a 5 would be 4+0+1=5 and so on.
The rotary switch was set at the first digit (the left digit) position 4 and the indicator will be on either no or yes once you fire the weapon . If it is no don't don't use the value 4 for digit 1 if it yes then use the value 4. Rotate the switch clockwise and check value 2 for yes and no. Rotate the switch clockwise to check value 1. Now the first (left) digit is the sum of your results for every digit that displayed a yes on the meter. (Remember it will be between 0 and 7.)
Repeat the process for the second, third & forth (right) digits. You will end up with a 4 digit count that has no single digit greater than 7. Something like 3721, which is a muzzle velocity (MV) of 1999 with a 10 ft spacing in my book.
6) Take the 4 digit octal code you recorded and look it up in the tables.
That is all there is to it. I may be a little odd when you first start using the model 12 because of the octal values but once you follow the process a few times then it will become second nature.
If you don't have the tables I can scan my copy into a pdf and email it to you. Might take a bit of time but the price is right, just a thanks.
Have fun ............... JP