Thread: "Trueing" BC/Velocity

Your elevation looks fine to me. If you're aiming the center of the plate, your dope seems correct.

I verify the BC with the following process
1. Measure the muzzle velocity
2. Use muzzle velocity with bullet BC to estimate the drop and terminal velocity at a known distance.
3. Use silvermountain/shotmarker to measure the terminal velcity and the actual drop.


Although the electronic targets are considered not accutate enough, I'm usually getting averaged < 10fps difference between the predicted terminal velocity from Applied Ballistic, versus the measurement from the electronic targets at 600-900yds.

Originally Posted by eamars

Your elevation looks fine to me. If you're aiming the center of the plate, your dope seems correct.

I suspect Gimp has adjusted dope to get to where he is and now is asking if he should adjust either BC or Speed to line up

Originally Posted by Gibo

I suspect Gimp has adjusted dope to get to where he is and now is asking if he should adjust either BC or Speed to line up

To be clear, I'm setting up a strawman to test other's thinking, not genuinely asking for advice

Originally Posted by gimp

To be clear, I'm setting up a strawman to test other's thinking, not genuinely asking for advice

Greetings @gimp,
Assuming you have a half decent chronograph I suggest you use your measured velocity. If you want to measure your down range velocity you may want to consider joining your local NRA club so you can use the Silver mountain kit. This will either correct or validate the predicted velocity. If the downrange velocity checks out then any difference in trajectory in likely to be operator error (sorry). If you can't measure down range velocity and wanted to change your predicted trajectory then I would adjust the BC and not the velocity. In spite of what some believe BC varies from shot to shot and day to day. I would also do some test firing at 300 metres to see how trajectory matches prediction. Last as mentioned above a decent aiming mark on you 600 metre target would help.
Regards Grandpamac.

Originally Posted by grandpamac

Greetings @gimp,
Assuming you have a half decent chronograph I suggest you use your measured velocity. If you want to measure your down range velocity you may want to consider joining your local NRA club so you can use the Silver mountain kit. This will either correct or validate the predicted velocity. If the downrange velocity checks out then any difference in trajectory in likely to be operator error (sorry). If you can't measure down range velocity and wanted to change your predicted trajectory then I would adjust the BC and not the velocity. In spite of what some believe BC varies from shot to shot and day to day. I would also do some test firing at 300 metres to see how trajectory matches prediction. Last as mentioned above a decent aiming mark on you 600 metre target would help.
Regards Grandpamac.

I have a magnetospeed v3.

Originally Posted by gimp

I have a magnetospeed v3.

All the more reason not to fiddle with the velocity then.
GPM.

Originally Posted by gimp

I have a magnetospeed v3.

So if you have a 9g bullet with mv about 2500 fps and a 4500g rifle that will Be recoiling backward at about 5 fps by the time the bullet passes the magnetospeed you would need to subtract 5 from the measured velocity ?

Originally Posted by eamars

Your elevation looks fine to me. If you're aiming the center of the plate, your dope seems correct.

I verify the BC with the following process
1. Measure the muzzle velocity
2. Use muzzle velocity with bullet BC to estimate the drop and terminal velocity at a known distance.
3. Use silvermountain/shotmarker to measure the terminal velcity and the actual drop.


Although the electronic targets are considered not accutate enough, I'm usually getting averaged < 10fps difference between the predicted terminal velocity from Applied Ballistic, versus the measurement from the electronic targets at 600-900yds.

Greetings @eamars and all,
That is exactly what I have done and found measured velocity at the target was very close to estimated, less than 10 fps. I did not measure the drop as I had done a rough zero using a tall target for 600 yards. I am a beginner at F-class and this was my first attempt at 600 yards so I was quite pleased.
Regards Grandpamac.