Ballistic Calculator / Chrono Inaccuracies

[Mike Islander]

Fair point. In the end it doesn't matter so long as the gun shoots where it's supposed to at the distances I need it to I suppose. I was just curious if there was something missing in getting from point A to point B.

I think Formidilosus has a good section on this somewhere on here. The thread may even have a similar title, but I'll have to look around.

 

[Shō[t]gun]

Make sure your point of impact is dead on at 100 yds. I was doing the same thing but my zero was about 1/2 moa high (touching the top of the bullseye), which then turns into 2 MOA high at 400 yds.
I did also estimate my actual velocity to be a bit different than what my chronograph measured after shooting groups at distance and observing the drop.

Did you mean to say 2 inches at 400y? 1/2MOA POI offset is the same regardless of distance, but would equate to 2" at 400y.

 

[parshal]

I shoot my drops out to 600 and play with the velocity in the bc calculator until everything lines up. I’m not sure this is the correct method but it works for me. Best wishes

If I have to change my velocity more than about 25 fps from chronograph to match drops at 600 I change BC. Nearly every time I change BC to match my drops at 600 it matches out to 1500 or so.

Don't be afraid to change BC. Even Berger verified BC will need adjustment for an individual rifle.

 

[Shō[t]gun]

Have you done a tracking test on your scopes to make sure they're spot-on and repeatable? Was there wind affecting the aerodynamic jump vertical adjustment that wasn't accounted for? 10mph left vs right will change your vertical POI by .5 even on a slippery bullet.
Either way, BC isn't static so just adjust it to what hits at distance on a calm day and call it good.

 

[Hoosker Doo]

Did you mean to say 2 inches at 400y? 1/2MOA POI offset is the same regardless of distance, but would equate to 2" at 400y.

Haha your math is correct... however, with real world variables, when I shot at 400 I was 2 moa (~8") high. Most of that was taken care of by getting a true zero, but I did also adjust my chronographed muzzle velocity up by about 70 fps to match what the bullet was actually doing.

PS - scope is Trijicon credo hx
Chronograph is magnetospeed sporter

 

[Shō[t]gun]

Haha your math is correct... however, with real world variables, when I shot at 400 I was 2 moa (~8") high. Most of that was taken care of by getting a true zero, but I did also adjust my chronographed muzzle velocity up by about 70 fps to match what the bullet was actually doing.

PS - scope is Trijicon credo hx
Chronograph is magnetospeed sporter

Got it, just sounded like you were equating the entire 8" difference to the zero being a tiny bit off, which only accounted for 2". The other 6" was purely a velocity issue.

 

[Shraggs]

I think Formidilosus has a good section on this somewhere on here. The thread may even have a similar title, but I'll have to look around.

I have set up couple of rifles now using his methodology. Generally it excludes using a chronograph due excessive variation. For grins I have done just 4 shot strings with mine. Then I take it appropriately long and adjust mv to get elevation.

Interesting that mv was trued up at the low end of my ES in both cases. Ie my 223 with UM loaded ammo 4 shot string 2803 with 32 fps spread. When I shot at 800 my adjusted up trued speed in my app to 2770.

 

[Bobbymac1842]

Fair point. In the end it doesn't matter so long as the gun shoots where it's supposed to at the distances I need it to I suppose. I was just curious if there was something missing in getting from point A to point B.

I agree. You have to validate all calculations before you order a custom turret. Those can change for many reasons. Humidity, temperature, variances in bullets, etc.