Trueing muzzle velocity vs BC

[RockyMtnMT]

Wasted a lot of bullets and powder before we got good chronographs. We now use Labradar and or magspeed. I need things to be simple, so I adjust bc to match my long range drop. We get out and shoot long fairly often in the same location. The solution will change from day to day with the same rifle combo. The solution definitely changes from rifle to rifle. The more we shoot long the shorter the range that I am willing to shoot at game. If I am going to take a shot past 700y on a game animal in the future, I will take a sighter on a nearby rock 1st, then adjust and take the shot on the animal. If the animal doesn't stick around for this, then it wasn't meant to be.

 

[nksmfamjp]

I set my velocity by Labradar. I set my BC by bullet maker data. Then I adjust zero to get to 300. After that, I adjust bc to kind of a best fit.

 

[WiscGunner]

1) If you don't have a MagnetoSpeed or Labradar chronograph, zero at 100yrds then measure your drops at midrange (400-600yrds) to calibrate your velocity in an ballistic solving app.

2) if you do have a quality chronograph, trust it. I use a magneto speed distanced from muzzle same everytime using one of the spacers for consistency. I then trust that velocity. I setup a rifle profile for summer temp and one for winter temp. I then tru BC to get dope to match my ballistic solver.

Phone Apps
Phone App ballistic solvers almost all use the same math so pick your flavor or fashion of standard apps (Strehlok, Shooter, AB, JBM Desktop, BallisticsARC,etc).
I prefer the interface of BallisticsARC, hate the interface of AB. Have used both with equal problems as they use the same math but AB is relegated to just a bullet library for starting BC's.

I find the math on these apps to be pretty decent inside 800yrd but needs a separate truing at 800 if shooting beyond 1000 as the theoretic arc doesn't match up and you need two "humps" to the theoretical arc to mimic matching the actual arc of the bullet. These app's mathematical errors are like using dial calipers. Truing the caliper with a pin gauge gives you a window of accuracy before the errors build up to a noticeable level. You don't true a caliper with a 1mm pin to measure a 30mm part.

I find Trasol to be spot on for short and long range without recalibrating. Trasol uses completely different math as does Hornady 4Dof.

If you are using a "standard math" solver it is very important to use multiple BC's as these app algorithms heavy rely upon the BC number with changes with velocity. This is why Hornady and Sierra provide "banded" bc's. Banded BC's are like calibrating your calipers with numerous pins. If you are only using one BC input in your standard solver you are only calibrating your data for one set of distance. Faking your weather or velocity data to compensate for bad BC input or inherent error in solver math is not a solution in my book but seems to make lots if people happy to do so.

Trasol and 4Dof are not so reliant on the BC as such a significant component in the equation.

But don't take my word for it or anyone else's, test it out for yourself. Download different apps to see what User Interface you enjoy the most, then compare calculations from the different formulas (Trasol,4Dof, all others) and see how they line up with your real world data.

 

[Hugnot]

Hopefully we will see more ballistic tools that don't use BC's like the Hornady 4DOF method. The BC is only a comparison to some standard. Many variables as the bullet plows thru an ocean of air.

From Hornady:

"Why calculate a trajectory using a mathematical comparison of your bullet to a "Standard Projectile" (oversimplification of BC) when you can use an exact model of your projectile in the trajectory calculation (Drag Coefficient)? Using Doppler radar, Hornady ballisticians have calculated the exact drag versus velocity curve for each projectile in the 4DOF®​ Bullet Library. Ballistic Coefficient can change as velocity changes. A drag curve doesn't change; the curve is specific to each projectile and is directly related to its trajectory."

 

[Reelamin]

Dont know what they call it....i guess velocity. Shoot real world and compare to the ballistic program and kestrel data. Then adjust velocity to match actual POI to what ever yardage I'm willing to shoot game at with that cartridge and bullet.

 

[Starlite]

This is my new findings:
No more proving at 600m or beyond (in reality beyond 800 for high BC LR pills)
Simply using the data from the LabRadar as per extreme reloader video; input the velocity and BC into your StrelokPro or Hornady app or in my case the Sig BDX. Tested today and was very accurate.

 

[BrentM]

This is my new findings:
No more proving at 600m or beyond (in reality beyond 800 for high BC LR pills)
Simply using the data from the LabRadar as per extreme reloader video; input the velocity and BC into your StrelokPro or Hornady app or in my case the Sig BDX. Tested today and was very accurate.

Pretty much my findings too. I've had very good success using ab profile for bc or hornady step bc. Labradar the fps, input the bc, and verify. Rarely need much if any tweaking. Seems that stuff is pretty dialed in these days and apps all use similar logic.

 

[jasent]

I've rarely ever had to true anything. The few times I did was for the trans sonic to sub sonic area of flight. Even then it was minimal
Only bc never velocity

 

[Starlite]

I've rarely ever had to true anything. The few times I did was for the trans sonic to sub sonic area of flight. Even then it was minimal
Only bc never velocity

100% agree. I'm now going back through my LabRadar data and truing the BC Of many loads. My theory is; By Truing these BCs, I'll accomplish successful hunting at longer distances while using less resources.. a Theory needing some testing (resources) . who doesn't like shooting!!

 

[nralifer]

Just for information purposes. I shoot out to 1300 yards for practice but now a days, I limit myself to 800 yards on game. I have a lab radar and trust it's numbers. I myself think the BC of a bullet can change depending on which barrel it's shot out of. I will change the BC of the bullet to match my drops on target. But in the grand scheme of things, changing whichever one to match your on target results is going to work.

I use a kestrel 5700 w/ LINK and AB paired with a Leica 2800.com. Works awesome! I range and the kestrel gives me my elevation and windage (after I check the wind with the kestrel).

You can use the Lab Radar to get a G7 BC if the bullet tracks 100 yds or more. I use the Kestrel for the environmental conditions and take the average G7, calculated for each shot, of 5-6 shots. The average G7 BC you get correlates quite well with AB Bullet Library data for the same bullet. Additionally you can use that BC since it is one you calculated for that gun/bullet combo. If you are using a boat tail bullet, G7 works since it is far less dependent on velocity.

 

[med358-boise]

Maybe I am not smart enough or experienced enough to undertsand this discussion; however, I am not sure what the point of "trueing" would be especially because BC changes as the velocity diminesions down range.

It would seem to me the only valid exercise (and the approach I use) is to 1) take my chronographed velocity and the published BC as the starting to point and 2) determine my maximum range for that rifle and validate calculated drops by actual shooting.

I have found that validation is only really necessary beyond 350/400 yards and is only necessary in 50 yards increments.

I have a self imposed limit of 600 yards and then only under perfect conditions and then only on elk sized game.

 

[dfanonymous]

Maybe I am not smart enough or experienced enough to undertsand this discussion; however, I am not sure what the point of "trueing" would be especially because BC changes as the velocity diminesions down range.

It would seem to me the only valid exercise (and the approach I use) is to 1) take my chronographed velocity and the published BC as the starting to point and 2) determine my maximum range for that rifle and validate calculated drops by actual shooting.

I have found that validation is only really necessary beyond 350/400 yards and is only necessary in 50 yards increments.

I have a self imposed limit of 600 yards and then only under perfect conditions and then only on elk sized game.

BC is a modeling of a bullet design that is usually not the bullet someone is shooting. It's accurate, sure, but it's not perfect. Those imperfections show up the further out you go. Namely around transonic and subsonic.

Trueing, simply is a process to align your data to match real world results. So, if not using a custom drag model, one might tweak or note numbers where a particular BC is most accurate. For hunting, especially within 600y, you will only be slightly outside max PBR for most common cartridges you'll see used in field…so one might not notice huge data issues so close.

 

[BrentM]

Maybe I am not smart enough or experienced enough to undertsand this discussion; however, I am not sure what the point of "trueing" would be especially because BC changes as the velocity diminesions down range.

It would seem to me the only valid exercise (and the approach I use) is to 1) take my chronographed velocity and the published BC as the starting to point and 2) determine my maximum range for that rifle and validate calculated drops by actual shooting.

I have found that validation is only really necessary beyond 350/400 yards and is only necessary in 50 yards increments.

I have a self imposed limit of 600 yards and then only under perfect conditions and then only on elk sized game.

Already well said above my comment but there is not much to be concerned about with in your range. This type of stuff becomes more of an issue at longer ranges or using low bc and low velocity ammo. For example shooting 223 55 grain bullets to 1000 vs an 88 grain. Big difference in bc and speed as well as design that may show up inside of 1000. Shooting higher BC bullets designed for LR with decent velocity you may encounter issues sub 1000 but most likely it will npt be noticeable until hitting 1200 plus.

 

[nralifer]

Already well said above my comment but there is not much to be concerned about with in your range. This type of stuff becomes more of an issue at longer ranges or using low bc and low velocity ammo. For example shooting 223 55 grain bullets to 1000 vs an 88 grain. Big difference in bc and speed as well as design that may show up inside of 1000. Shooting higher BC bullets designed for LR with decent velocity you may encounter issues sub 1000 but most likely it will npt be noticeable until hitting 1200 plus.

Here is a potential curve ball. Some years ago, probably 3-4, we were testing a prototype .338 bullet weighing 260 gr with an average G1BC of 0.813 over 1250 yds and measured with an Oehler 88 system. We then took it out to 2900 yds. Altitude was about 1400 ft. Using the Oehler we measured the average G1BC of 0.90! It remained stable through the transition through to subsonic which happened at about 2400 yds out, so the bullet traveled subsonic for 500 yds before impacting the target creating a perfect round holes. The cartridge was a 338 Lapua Mag AI and initial MV was 3020 fps or so as I recall. We had several impacts using the G1 BC 0.813. How do you explain the increase in BC with subsonic transition?