Labrador vs ballistics chart speeds

[Mikecr]

Your statement just made me question how I put in data. Why leave Altitude at 0?

Temperature, Absolute Pressure(station pressure), and Relative Humidity are the parameters from which air density is calculated. Where you don't have measure of these you can alternately enter altitude and the software would lookup 'standard conditions' for altitude. But what then do you enter for the fields which would otherwise lead to calculating actual air density?
That's where some software allows Density Altitude entry, which should override all other fields. But many folks get this all confused with altitude, or pressure altitude, and they forget that DA is calculated from what you had to measure and enter anyway (Temperature, Absolute pressure(station pressure), and Relative Humidity.)..

Now if all you have is 'barometric pressure', which is sea level corrected, and as reported by airports, then(only then) you would have to assign the altitude that pressure is adjusted to. This, so that your software can back calculate absolute pressure, so that it can figure out air density.

I can recalculate drag and form factor for different conditions to adjust G1BC or G7BC instead of having ballistic software do this (like if it was weak in this function).
For instance, this .387 G7BC bullet (at ICAO and assumed 2850fps) has a local G7BC of .379 at 34degF, 0%Rh, and 29.96"Hg sea level corrected at 925' ASL.
But some software tracks w/resp to Mach #, and this is affected by the same air density parameters, so again the parameters really need to be entered explicitly.

This is the stuff most folks get befuddled on with ballistic software entries. It's hard to remember. So we should forget ALTITUDE,, and think AIR DENSITY (what matters).
Easiest to do this is simply measure the direct parameters needed by your software for air density. Temperature, Absolute pressure(station pressure), and Relative Humidity. Leave all other trickery at zero.

 

[rockwallraider]

I would doubt the scope before doubting lab radar. I have checked several scopes over the last couple months and very few track to .25 moa

 

[tdot]

Awesome. Thanks for that very detailed answer
Makes it much easier to understand.

 

[Tree Farmer]

I'm going to ask a stupid question, so try to be gentle. If you can actually measure/verify bullet drop (and actual scope adjustment) to 1000 yds., why do you need the data to match a ballistic calculator? This is coming from a guy that never killed anything beyond 400 yds., but hope's to become proficient to 600 yrs. +.

 

[GoosePilot]

I want to use a ballistic rangefinder and I live at 900ft and hunt 3000-13000ft on days that might be -10 to 90 degrees from flat to 30 degree up/down

 

[cohunt]

so I guess Labrador's are not very aerodynamic as I could not seem to find any Labrador ballistic charts-- I did find an interesting chart that shows that their temperatures actually change depending on time of year --learn something new every day

yes I know it was just a finger fudge, but every time I look at the thread title I think of flying labrador's

 

[Tangent]

Have never used a ballistics program before in this way.

Today I zeroed my z5 by at 200. Shot 100 to 1000 at every 100 interval. Lab radar shots from 500-1000. All shots done over about a 4 hr span. It was 32 when I started and 35 when i finished. Ammo was in garage at 60, then sat outside for 30 min before starting. H1000 on other 50-60 degree days shot 2850fps. Today they started around 2840ish and dropped to 2820ish by the end (as powder cooled off I'm sure). Avg for the 13 rounds recorded was 2830. Shot 24 total. It shot extremely well at all ranges imho.

Question is when i put my data into a half dozen different programs (they were similar) I had to enter 2670fps to get chart numbers to match my recorded turret settings.
It's a z5bt 3.5-18, 20moa rail, low rings. 1.75" above center, 925 ft asl, 34 degree, 29.96, wind at 7 increasing to 12 over 4 hrs at my 6 o'clock
Berger eol 195, g7 .387
300 - 2.5 moa
400 - 5.25
500 - 8.5
600 - 12.5
700 - 15.5
800 - 18.5
900 - 22.75
1000 - 27.75

Like others have mentioned, I would think this is a scope issue. Swarovski looks to state that adjustments are 0.25 in/100 yards - I think your scope is IPHY (aka SMOA) not TMOA, which is approximately a 5% difference.....your velocity 'correction' is about 5.6% (not apples-to-apples but shows a relatively similar order of magnitude error).

Again, as others have mentioned, your scope may or may not track, which could lead to even bigger errors.

I always have to 'true' velocity to match real world dope, but we're talking about a 0.5% or less adjustment in velocity to match out to ~700 yards. Similar with BC, very minor tweaks to make everything all match up to ~1,400 yards.

 

[LongBomber]

Do you have a place where you can shoot the same target from 100 to 5 or 600 yards? One tall target (say 60") with an aiming dot at the top. You shoot this every 100 yards with no dialing of the scope. You can measure actual drop right off that target.

I would do that and a tall target test for the scope.

 

[GoosePilot]

Yes i shot 500 down to 100 moving closer to target without moving turret. Then i zeroed scope and shot 200, 500,6,7,8,9,1k