^^ Exactly. If it is not open all the way, the screens are closer together, making readings high. I find I have to be at least 15 feet away to get consistent readings.
Trying to understand chrono readings
- Thread starter litledab
- Start date
^^ Exactly. If it is not open all the way, the screens are closer together, making readings high. I find I have to be at least 15 feet away to get consistent readings.
The Chrony people used to test their units on the range here at the farm. I learned a lot by watching and listening.
They had a long plank that held an Ohler in the middle and 7 Chronys. They would fire a shot through all of them and note the readings. The Ohler screens were separated by double the usual distance, to enhance accuracy. They shot a 243, a 308, a 22, a BB gun and an arrow.
The total spread in readings was about 50 fps. The difference between units was always about the same. Chrony A was always about 30 fps faster than the Ohler while Chrony B was always about 15 fps slower (for the 308 shots) .
Bullet path. The Chony has a very high clock speed. It is sensitive to the path the bullet takes through the screens. For best accuracy, aim at something from a fixed firing position.
Light. The screen look up and see the bullet. They see better if there is a cloud rather than a blue sky. On a clear day, use the diffusers.
Muzzle blast. Back up at least 15 feet.
The three variables above can lead to poor results.
They had a long plank that held an Ohler in the middle and 7 Chronys. They would fire a shot through all of them and note the readings. The Ohler screens were separated by double the usual distance, to enhance accuracy. They shot a 243, a 308, a 22, a BB gun and an arrow.
The total spread in readings was about 50 fps. The difference between units was always about the same. Chrony A was always about 30 fps faster than the Ohler while Chrony B was always about 15 fps slower (for the 308 shots) .
Bullet path. The Chony has a very high clock speed. It is sensitive to the path the bullet takes through the screens. For best accuracy, aim at something from a fixed firing position.
Light. The screen look up and see the bullet. They see better if there is a cloud rather than a blue sky. On a clear day, use the diffusers.
Muzzle blast. Back up at least 15 feet.
The three variables above can lead to poor results.
Over 2800 doesn't sound right with 168gr and .308. Looked at my ladder test notes for my .308 and with a similar rifle (5r 24" 1/11.25 twist) 44.5gr Varget, Hornady 168grBTHP, S&B LR primer, Lapua brass, light crimp and I get ~2655 average on a Magnetospeed chrony. Another ladder test for a 20"barrel .308 gives about 120 f/s less on average. Don't know how right it is but I was getting 3150-3440 f/s on a ladder test yesterday with my new .223 which made perfect sense.
