Thread: Ballistic truing conundrum

Thanks all for the comments and feedback. To pick up on a couple of points above :

BC - i used 0.67 G1 as listed by Hornady. If anything manufacturers stated BCs tend to be “optimistic” and derived under ideal conditions. In my case if a lower BC were correct this would not explain the data I’m getting. Dialing 9.0 moa compared to ballistic program 10.12 moa. A lower BC would require a bigger come up, not smaller. Or conversely the BC would need to be up around 0.7 or something to make the numbers line up.

Chrony error, using a Magneto Speed. Have used on many other rifles previously and not observed it to be inaccurate previously. Every measuring device has a degree of precision or error, so possibly 1-2% out ? But to get the observed come up difference of 9 vs 10 moa requires a muzzle velocity of ~3100 fps compared to my measured 2995. Just can’t see 3100fps being possible with a 22in bbl SAUM. Wouldn’t it be nice though !!

Scope dial up calibration - did that today with tall target at 100.0 yards measured at the erector. Surprisingly the VX6 is dialing better than moa !!
First time I’ve seen this in a Leupy or any scope for that matter. This one is dialing 1.083in per moa, instead of 1.05in/moa. That translates to a 3% error. So dialing 9.0 moa is actually giving a come up around 9.2 moa.
So this still leaves 0.75 - 0.8 moa “unexplained”.
Or my muzzle velocity is something like 3075fps ?

At this point my guess is I’m dealing with several compounding errors.
1. Scope dial up
2. Zero maybe slightly out, should be able to verify this next weekend at NZDA range if weather plays ball.
3. Chrony might be reading slightly low

I agree @Beetroot, running checks at 300 &/or 500 yards would be wise and helpful.

Originally Posted by chainsaw

Thanks all for the comments and feedback. To pick up on a couple of points above :

BC - i used 0.67 G1 as listed by Hornady. If anything manufacturers stated BCs tend to be “optimistic” and derived under ideal conditions. In my case if a lower BC were correct this would not explain the data I’m getting. Dialing 9.0 moa compared to ballistic program 10.12 moa. A lower BC would require a bigger come up, not smaller. Or conversely the BC would need to be up around 0.7 or something to make the numbers line up.

Chrony error, using a Magneto Speed. Have used on many other rifles previously and not observed it to be inaccurate previously. Every measuring device has a degree of precision or error, so possibly 1-2% out ? But to get the observed come up difference of 9 vs 10 moa requires a muzzle velocity of ~3100 fps compared to my measured 2995. Just can’t see 3100fps being possible with a 22in bbl SAUM. Wouldn’t it be nice though !!

Scope dial up calibration - did that today with tall target at 100.0 yards measured at the erector. Surprisingly the VX6 is dialing better than moa !!
First time I’ve seen this in a Leupy or any scope for that matter. This one is dialing 1.083in per moa, instead of 1.05in/moa. That translates to a 3% error. So dialing 9.0 moa is actually giving a come up around 9.2 moa.
So this still leaves 0.75 - 0.8 moa “unexplained”.
Or my muzzle velocity is something like 3075fps ?

At this point my guess is I’m dealing with several compounding errors.
1. Scope dial up
2. Zero maybe slightly out, should be able to verify this next weekend at NZDA range if weather plays ball.
3. Chrony might be reading slightly low

I agree @Beetroot, running checks at 300 &/or 500 yards would be wise and helpful.

If you are using the kestrel use the bc data on the kestrel phone app.
A g1 bc for the saum will not be correct.
Either use the kestrel g7 or custom drag curves it comes with.

Sent from my SM-A226B using Tapatalk

Originally Posted by chainsaw

At this point my guess is I’m dealing with several compounding errors.

This. Accuracy is minimising all of the errors you can so that the ones you can't have a smaller effect (eg meteorological factors).