Ballistic Coefficient - Calculating

[billmeek]

I've been learning how to use the ballistic apps and found that often the BC found online for 22LR ammo was close, but not good enough. I started out using Strelok Pro and finally just bought a Kestrel 5700. I was still close, but what I needed was correct BC. So I fired 50 rounds and gathered data using a LabRadar, put the data into the JBM online calculator (ignoring any suspicious values), averaged the BCs, and that's what I put into the Kestral. What I found interesting is the same ammo (CCI SV) fired from different rifles (Mark II FV-SR and B22 FV-SR) with the same length barrel gave slightly different BCs.

At 500 yards, the Kestrel elevation was then spot on from the B22 using CCI SV.

For the B22 with CCI SV 0.124 is the my calculated BC.
For the B22 with Agulia SV 0.114 is my calculated BC.

 

[MDrimfirerookie]

were you using 2 chronographs to gather your data for the JBM online calculator? otherwise, how did you get the near and far velocity values?

 

[flatland1]

Doesn't the LabRadar unit give downrange velocity data, as well as muzzle vel?

 

[billmeek]

The LabRadar provides a couple of spreadsheets in Excel format. The series spreadsheet (the one I used) provides a calculated velocity and kinetic energy at the muzzle and real data from ranges of 10/25/50/75/100 yards. Each individual shot also has it's own spreadsheet that provides velocity and distance every .002 seconds from the distance the LabRadar picks up the round (averages around 6 yards) until it can't pickup the bullet anymore (much greater variance but often ~100 yards). At 22 SV speeds, you get a little bit more than a value per yard. Given the SNR (signal to noise ratio) at the longer ranges with the small bullet, I chose to use 10 and 50 yard data as the most accurate values while still providing the necessary spread for the online calculator.

 

[billmeek]

I just got back into shooting this last year after a 30-year hiatus. Back then I knew very little about ballistics. Basically I pointed and shot.

A lot of the enjoyment I'm having right now is shooting with the NRL22 guys locally. I am, however, far from being competitive even on the local level... much less at the national level. About the only stages I do well on are the prone. I'm just not that steady on all the positional stuff. It doesn't matter though as I am really just having a blast being out there.

Chasing 22LR accuracy and learning all of the ballistics can help in the NRL22. Especially when the local match director is the evil individual who puts a paper stage at 100 yards (December 2018 course of fire). <grin> I could just get by shooting on DOPE, which I still use, but mainly I'm doing this for me as it's something I find interesting.

 

[bmicek]

I always use my app (Strelok Pro) to give me a baseline. I'll chrono my rounds and get an average velocity, plug it into the app, and then shoot at a given yardage to see if what the app is giving me is trued to what I'm shooting. If not, I true my data (typically true the BC) and end up with data on hand for the NRL22 matches I shoot. I trust the data it gives me because in a sense I spoon feed it with the results I'm printing on my targets. I guess in a sense you could say I live and die by my app but thats only because I don't walk away content unless what it is giving me for holdovers matches up with what I'm seeing down range.

 

[billmeek]

Where are you getting the weather data for Strelok? I bought one of the Weatherflow meters, but found it too finicky to use.