Adjusting bc or velocity to match drop

[105Coues]

Thanks for clarifying.

 

[HTJ]

I shot out to 1150 yrds today with the 215 bergers at 2800 fps. The stated bc is .696 to match my actual drop I had to change the bc to .610. That put my horizontal at 32 moa which was perfect. It also worked at 705 yrds. Also I was shooting from the south to the north. You guys that have done this before, does that seem normal, to adjust the bc that much? I made sure my other atmospheric settings were correct. Also my scope has been through a tall target test and tracks correctly. Thanks! These are the 3 shots at 1150. The two upper are the ones after the correction.

Use the G7 BC
True your rifle at the distance your load hits a velocity of 1340 FPS
Use a kesteral to determine this distance
Use a bar roughly 6 inches tall 3 foot long to true up. Start hitting low adjust to where you shoot Just over the top than walk it down until dead on at the determined distance.
Test your new calculations MOA or Mils at 200, 600, 800, 900, 1200. Now you will know your correct velocity to use in your data.
Use Density Altitude
Good luck

 

[OrionsStar]

You gotta love this stuff! Ive been spending too much of time and money and I can't get enough! LOL!

 

[Tumbleweed]

Scope tracking, scope tracking and scope tracking. That's where I'd start. Do a tracking test at 100 yards and see what you come up with. From the sounds of it and from what I've experienced this could easily be playing into your error. It may not account for all of it but probably some. I mount scopes in a solid fixture separate from the rifle to do tracking tests and they are ALL OFF to some degree. My Burris' seem to undertrack very slightly and Leupolds typically overtrack a lot.

2nd, I'd recommend using Custom drag curves. There's no more messing with B/C's at different distances to make drops match. You zero, shoot once at distance to check drops and then put in a correction factor (if needed) to correct for your rifle's difference in regards to the established drag curve. Done. I use Hornady's 4DOF program...it's free. There's also Applied Ballistics which is in the $30 range.

 

[eklarsen]

I agree you should use the G7 which would take some of the velocity questions out of the equation

 

[Joefrazell]

The scope over tracks by 2%. I had some weather variables slightly off and that's what my issue was. I shot again a couple weeks ago at 1200 and all was well. At these ranges everything needs to be dang near perfect. I feel the actual shooting is the easiest part.

 

[4xforfun]

One of the things you asked about that didn't get addressed....shooting north/south. North/South shooting has zero affect on vertical bullet flight.

Now, start changing that by a few degrees E/W and elevation comes more and more into play due to the earth's rotation...which will be at 100% value when you are shooting due E/W. Now. I can't remember if the difference changes more or less (or same) as you move away from the equator. My memory is fading rapidly....like the velocity of a 150 grain flat nose out of a 30/30.

Tod

 

[Bravo 4]

The closer to the equator the more the error increases when shooting east/west.

 

[4xforfun]

The closer to the equator the more the error increases when shooting east/west.

I assume the Shooter app knows the difference since it asks the lattitude you are at when inputting your data. I just never played with the numbers to see because, well, I guess I don't care that much. I'll be hunting the US Canada border for the rest of my life. Simply input 49 degrees.

Tod

 

[Bravo 4]

Yes sir, that's the point of inputting latitude. The earth is spinning faster at its thickest circumference, the equator. There it spins at a little over 1,000 miles per hour, the further north or south you go it gets slower. You are probably getting close to half that.
I was taught the high/low impacts of shooting east/west is the Eotvos effect and the right/left is Coriolis.

 

[4xforfun]

Yes sir, that's the point of inputting latitude. The earth is spinning faster at its thickest circumference, the equator. There it spins at a little over 1,000 miles per hour, the further north or south you go it gets slower. You are probably getting close to half that.
I was taught the high/low impacts of shooting east/west is the Eotvos effect and the right/left is Coriolis.

Yep...1/2 would be the 45th...I am at the 49th...so, less than half.

 

[Canadian Bushman]

Definitely use g7 bc

Strongly suggest using AB and custom drag curve.

Get an average mv reading from a reliable source using more than just a few rounds, then dont change it.

Bc can change from lot to lot. True bc from the furthest range possible where the mv is >,= mach 1.2

Custom drag curves will plot better through transonic into sub sonic range.

 

[DavidleeCole]

I know only what I have read and what I have been shown and it works for me in the field. Kestrel for all atmospherics, IR temp for my ammo, actual range for all atsmophric and wind adjustments, true horizontal range for my gravity drop this is what I feed my ballistics and it comes out pretty close. If I have any problems I check again all inputs I double check them before I shoot have been hasty in the past and that was the problem. After that I suspect my position and fundamentals of marksmanship. Then my weapon system if things dont change. Thirdly I will check my ammo to see I have changed something just slightly during reloading and make sure its consistency is good. If all that has not changed any thing I will shoot a good group of 5 to 10 rounds around 90% transonic and adjust BC as needed however if my vertical shoot desperation is great than I will not adjust any thing and just go back and recheck everything. I believe that good practice is not only just putting rounds on target especially those in the bull it's about learning why it did not happen that will stick with you the most. And the experience of trouble shooting is priceless for us and those we share it with.