Thread: "Trueing" BC/Velocity

3 shots, 600m.

Should I true my result from the ballistic app? How and what?

what is your thought process, for those that subscribe to the practise?

I'd just true speed from app and check it again at various ranges. What app do you use?

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 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.

i do, shoot at 4 different rangers and can use the app to make a nice average shooter has a bit that you punch in and it works out your curve.

edit to add that you use real-world drop so it accounts for, speed, bc & scope adjustment all in one

Originally Posted by gimp

3 shots, 600m.

Should I true my result from the ballistic app? How and what?

what is your thought process, for those that subscribe to the practise?


Attachment 247374

Futch i cant see that far,nice shooting.

That’s a very tidy group at 600yd. What was your POA? Assuming it was centre of gong then your vertical dispersion looks pretty small - maybe 1-2 in high at most ? I guess it depends on how big the steel plate is? If it’s 1.5 in high at 600 then that’s a 1/4 moa correction. Pretty minor. You certainly could increase muzzle velocity in app to see what speed equals 0.25 moa less than your dial up.
There’s appears to be more horizontal dispersion - right to left wind ? This might also mean a slightly high poi.
I use a small centre dot or square on the gong to ensure a precise pos.
I’d be tempted to repeat the excercise on another day with different conditions to see if you need to dope & how much

Originally Posted by chainsaw

That’s a very tidy group at 600yd. What was your POA? Assuming it was centre of gong then your vertical dispersion looks pretty small - maybe 1-2 in high at most ? I guess it depends on how big the steel plate is? If it’s 1.5 in high at 600 then that’s a 1/4 moa correction. Pretty minor. You certainly could increase muzzle velocity in app to see what speed equals 0.25 moa less than your dial up.
There’s appears to be more horizontal dispersion - right to left wind ? This might also mean a slightly high poi.
I use a small centre dot or square on the gong to ensure a precise pos.
I’d be tempted to repeat the excercise on another day with different conditions to see if you need to dope & how much

40cm square plate. Holding for R-L wind with intent to hit centre plate (POA). Did not call wind correctly but held consistent wind hold to shoot 3 shot group.

E: actually 38cm sq plate.

If there is any vertical discrepancy I cant attribute to wind then I adjust velocity in app untill it matches results.
My reasoning is as follows.
Bryan Litz bcs are probably pretty accurate.
My shooting chrony is probably within 100fps on a good day.

Originally Posted by veitnamcam

If there is any vertical discrepancy I cant attribute to wind then I adjust velocity in app untill it matches results.
My reasoning is as follows.
Bryan Litz bcs are probably pretty accurate.
My shooting chrony is probably within 100fps on a good day.

I agree. Tune mv to match real world. Should only be a few tenths out, otherwise something more serious is wrong e.g. zero or environmentals
True BC if I have access to significant sub-sonic range (e.g. 1k+)

Are you bloody kidding Gimp!!